WO2002050544A1

WO2002050544A1 - Multiple target test useful for pre-donation screening of blood

Info

Publication number: WO2002050544A1
Application number: PCT/GB2001/005792
Authority: WO
Inventors: Helen Lee; Jean-Pierre Allain
Original assignee: Helen Lee; Jean-Pierre Allain
Priority date: 2000-12-21
Filing date: 2001-12-21
Publication date: 2002-06-27
Also published as: AP1730A; OA12487A; AP2003002815A0; CN1486425A; GB0031391D0; AU2002216285A1

Abstract

Tests for establishing whether any of a plurality of different targets are present in a sample solution are described. If one or more of the targets are detected a positive result is obtained, but the different targets are not differentiated by the test, so there is no indication which targets have been detected. Such tests are useful for pre-donation screening of blood at public blood donation sessions to test whether the blood is safe for transfusion. The tests allow infected blood to be identified, but preserve the confidentiality of the reason for refusal of infected blood. This avoids the distress caused by public diagnosis of infection by diseases with which there is a social stigma attached, such as HIV. The tests are particularly suited for use in developing countries to screen for HIV, HBV, and HCV infection. Dipsticks and kits for performing the tests are also described.

Description

Multiple Target Test Useful for Pre-Donation Screening of

Blood

This invention relates to tests, kits, dipsticks, and apparatus for detection of multiple targets in a sample

/ solution and allow, for example, determination of whether a person is infected with any of a number of disease-causing micro-organisms. In particular, tests, kits, dipsticks and apparatus of the invention are for testing whether or not a person's blood is suitable for transfusion.

Transfusion or injection of unsafe blood accounts for 8-16 million hepatitis B virus (HBV) infections, 2.3-4.7 million hepatitis C virus (HCV) infections, and 80,000-160,000 HIV infections each year. In most resource-poor countries of Africa, Asia, and Latin America, post-donation screening by enzyme immunoassay (EIA) has revealed a cumulative prevalence of 5-20% for hepatitis B surface antigen (HBsAg) , anti-HIV antibody and anti-HCV antibody in blood donors.

Despite this high rate of infection, the blood supply in many developing countries is incompletely screened or not screened at all for HIV antibody. An estimated 5-10% of HIV infections in developing countries are due to blood transfusion. The WHO estimate that 50% of blood donations in sub-Saharan Africa are screened for HBsAg and only 5% for anti-HCV. The following table gives an indication of the prevalence of HCV, HIV, and HBV in some countries of Africa:

In many cases, blood screening is carried out after donation. However, post-donation screening in developing countries has several disadvantages . The high prevalence of viral infection means that much of the blood donated cannot be used. Thus, there is considerable wastage of materials such as blood bags and reagents . Tested and untested blood is often stored in the only available refrigerator at the blood bank, thus allowing considerable risk of confusion of safe and unsafe blood. In many cases it is difficult to inform patients found to be infected because they have no address or because there is no adequate means of communication, or because they live long distances away and so are unlikely to return to receive the results once the post-donation screening has been carried out.

In contrast, pre-donation screening allows considerable savings in materials and testing cost because the blood from potential donors found to be infected is not then drawn. Entry of infected blood to the blood bank facilities is thereby prevented. Patients found to be infected can be informed of the infection at the donation session. Appropriate counselling, treatment, and prevention of transmission can then be initiated immediately without having to require donors to return at a later date.

In some areas, such as sub-Saharan Africa, Thailand and

India, this pre-donation testing is carried out in public blood collection sessions. Persons who are found to be infected with a disease-causing micro-organism, thus making their blood unsuitable for transfusion, are advised of this at the session. Because the session is public, the identity of these persons is not kept confidential . This is of particular concern if a person is found to be infected with a disease with which there is a social stigma attached, such as HIV, as considerable distress can be caused to the person by such public diagnosis. In contrast, public diagnosis of other infections, such as HBV, HCV or malarial infection is much more readily accepted.

We have appreciated that there is a need to provide pre- donation tests which can be carried out in public to establish whether or not a person' s blood is suitable for transfusion without disclosing whether a person has an infection with which there is a social stigma attached.

According to the invention there is provided a test for establishing whether any of a plurality of different targets are present in a sample solution which comprises contacting the sample solution with a solid phase to allow capture of target present in the sample solution by the solid phase, and establishing whether or not any of the targets has been captured, wherein a positive result is obtained if one or more of the targets are captured but does not indicate which target or targets have been captured.

In preferred embodiments, tests of the invention are used to test whether a person is infected with any of a plurality of different micro-organisms or infectious agents thereby making their blood unsuitable for transfusion. Thus, preferably the sample solution is, or is derived from, a blood sample and the test is for establishing whether the blood is suitable for transfusion.

According to the invention a positive result shows that any one or more of the different micro-organisms or infectious agents are present. However, the test does not differentiate between the different micro-organisms or infectious agents. Thus, the person's blood is identified as unsuitable for transfusion but the reason for this is not indicated (not even the person carrying out the test is able to establish this from the result) and therefore remains unknown. The person is then simply informed that their blood will not be accepted for blood collection.

Subsequent testing, which can be carried out in a confidential manner, can then establish the reason why the person's blood is unsuitable for transfusion. If the person is then found to be infected with a disease causing microorganism with which there is a social stigma attached, the distress caused by public diagnosis of such infection is avoided.

The blood is preferably tested for any of the following: HIV, HBV, HCV, or malarial infection. Suitable markers of such infection comprise or consist of: an antibody raised against an HIV antigen; an antibody raised against an HCV antigen; an HBV antigen, preferably HBsAg; and a Plasmodium antigen.

Most preferably, the blood is tested for HIV, HCV, and HBV. In areas where there is a high prevalence of infection (10% or more) by one or more of these viruses, such tests allow a considerable saving to be made of the materials and costs (which can constitute 1/3 to 1/2 of the blood bank budget) which would otherwise be incurred by post-donation screening.

Although blood screening tests of this type are primarily designed to meet the needs of developing countries, they can also be useful in developed countries under circumstances in which a rapid test result is desired. An example is blood screening at inner city clinics. It has been found that up to 40% of the attendees of inner city clinics tested for HIV do not return for their test results and are often not traceable and therefore lost to the healthcare system. Tests of the invention allow pre-donation screening to be carried out so that infected attendees can be identified at their initial visit.

Tests of the invention may be used to test whether a patient is infected with other micro-organisms or infectious agents. Any marker of infection may be tested for. Examples include an antigen or nucleic acid of the micro-organism or infectious agent, or an antibody raised by the person to an antigen of the micro-organism or infectious agent .

Tests of the invention may also have wider application for testing whether a sample solution contains any of a plurality of different targets in circumstances where it is not desired or necessary to know which targets are present. The different targets are not necessarily markers of infection by a micro-organism or infectious agent. Other targets may include hormones, metabolites (for example to test for metabolic disorders) , illicit drugs, vitamins, steroids, or antibodies produced as part of an allergic reaction.

Tests of the invention are particularly suitable as screening assays where it is desired to know whether any of a number of different targets are present in a plurality of different samples . Because several different targets are tested for, the time and cost of separately testing for each target is avoided. Once a test has been carried out, only the positives need be re-tested to identify the particular target (s) present .

The different targets may be captured by capture moieties immobilised to the solid phase, and detection moieties may be used to detect the captured targets. Thus, according to the invention there is further provided a test for establishing whether any of a plurality of different targets are present in a sample solution which comprises : providing a solid phase having a plurality of different capture moieties immobilised thereto, each capture moiety being capable of capturing a different target; providing a plurality of different detection moieties, each detection moiety allowing detection of a different target captured by its capture moiety, detection of the different targets being such that there is no indication of which target or targets have been detected; contacting the solid phase with the sample solution to thereby allow capture of target by the capture moieties; and using the detection moieties to establish whether any of the different targets are captured from the sample solution.

There is also provided according to the invention a kit for establishing whether any of a plurality of different targets are present in a sample solution, the kit comprising: i) a solid phase having a plurality of different capture moieties immobilised thereto, each capture moiety being capable of capturing a different target; and ii) a plurality of different detection moieties, each detection moiety allowing detection of a different target captured by its capture moiety, detection of the different targets by the detection moieties being such that there is no indication of which target or targets have been detected.

Capture of the different targets should be such that there is no indication, for example by the position on the solid phase at which a target is captured, of which target or targets have been captured.

Where the targets are markers of infection by microorganisms or infectious agents, the capture moieties are capable of binding the markers . Depending on the target to be captured, a capture moiety may be an antibody or antibody fragment (capable of binding an antigen of the micro- organism or infectious agent) , a nucleic acid or nucleic acid analogue (capable of binding nucleic acid of the microorganism or infectious agent) , or an antigen (capable of binding an antibody raised against an antigen of the microorganism or infectious agent) . where the targets are markers of HIV, HCV, HBV or Plasmodium infection, preferably the different capture moieties comprise or consist of any of the following: an HIV antigen, an HCV antigen, an antibody to HBV, and an anti -Plasmodium antibody, and fragments or derivatives thereof .

The solid phase may be any solid phase on which capture and detection of the targets may be carried out . Examples of suitable solid phases include a dipstick (such as a nitrocellulose dipstick) , an Enzyme Linked Immuno-Sorbent Assay (ELISA) plate, or micro-particles (for example, beads) . Whether or not any of the targets has been captured may be established by any suitable method including ELISA, other methods of antibody detection - for example using labelled antibodies (labelled for example with radioactivity or preferably a colour label) , or by agglutination of microparticles .

In preferred embodiments of the invention, the solid phase is a dipstick. Dipstick tests are quick and easy to perform, can be carried out with minimum training, and do not require expensive equipment. Dipstick tests are therefore relatively cheap to perform.

Dipstick tests are especially advantageous for screening blood (particularly in developing countries) compared to other screening tests, such as microtiter plate enzyme immunoassay (EIA) tests . EIA tests require expensive equipment, are more complicated and slower to perform than dipstick tests, and need to be carried out by highly skilled technicians . In developing countries , many blood banks

(which are mostly located in hospitals) screen too few samples to justify the expense of performing microtiter plate EIAs . The cost of EIA tests is substantially higher where low numbers of samples are processed because there is a higher proportion of control wells in relation to test samples.

Dipstick tests may be performed by immersing the dipstick in a sample solution or adding a fixed volume of sample with or without a diluent to allow binding of target in the sample solution to its capture moiety immobilised to the dipstick. However, preferably the dipstick comprises a contact end for contacting the sample solution and is capable of transporting the sample solution by capillary action to a part of the dipstick remote from the contact end at which the different capture moieties are immobilised.

Preferably the different capture moieties are immobilised to a single capture zone of the dipstick. The different capture moieties may be interspersed with each other at the single capture zone. Preferably, however, the different capture moieties are not interspersed with each other but are immobilised at adjacent regions of the single capture zone and are contiguous with each other (as shown in Figure 1) . In such preferred embodiments, the capture moieties are not diluted by one another so the sensitivity of target detection is thought to be higher than for embodiments in which the capture moieties are interspersed with one another. The adjacent regions of the single capture zone should be close together so that they cannot be distinguished visually. The same visual result is then obtained no matter which target or targets are captured.

Alternatively, each different capture moiety may be immobilised at a different capture zone of the dipstick. As long as there is no indication of which target binds to which capture zone, and the tester is not informed of this, then tests carried out using such dipsticks will not indicate which target or targets have been captured. It will, however, be possible to tell the number of targets which have been captured.

Detection according to the invention using dipsticks with multiple capture zones is different to conventional dipstick detection of multiple targets where the tester knows which target binds to each capture zone. EP application no. 0301141 discloses a dipstick for simultaneously detecting the presence of a variety of specific antibodies in a clinical specimen. Different specific antigens used to capture the specific antibodies are separately immobilised to different capture zones of the dipstick. The capture zones are labelled so that a tester can identify which target binds to each capture zone .

In such conventional tests, it is desired to be able to distinguish the different targets and to identify which targets are present. Thus, a signal at a particular capture zone will indicate to the tester that the target for that capture zone is present . This is in contrast to tests of the invention in which it is desired to establish only whether any of the targets are present without establishing which of those targets are present . A signal at one of the capture zones will indicate only that one of the targets is present, and not which target is present, because the tester does not know which target is captured at that capture zone.

However, a disadvantage of using dipsticks with a plurality of different capture zones is that it is possible to deduce which target binds to each capture zone from the results of subsequent tests performed to identify which target (s) is present once a positive result using a test of the invention has been obtained. This could be avoided if the order of the capture zones is changed for different dipsticks .

The different detection moieties are preferably separate from the dipstick, but may be releasably immobilised to the dipstick. If the detection moieties are releasably immobilised to the dipstick, they should be released on contact with the sample solution so that they can bind to target in the sample solution.

Where a target is a marker of infection by an infectious agent or micro-organism, a detection moiety is capable of binding the marker. The detection moiety may comprise an antigen, an antibody or fragment thereof, or a nucleic acid or nucleic acid analogue. Binding of a detection moiety to its target may allow direct detection of the target, for example if the detection moiety comprises a label. Alternatively, binding of a detection moiety to its target may allow indirect detection of the target, for example, by a primary antibody capable of binding a detection ligand coupled to the detection moiety. The primary antibody may be labelled, or a labelled secondary antibody may also be provided which is capable of binding the primary antibody. In other embodiments, indirect detection may be achieved by conversion of a chromogenic substrate by a converting enzyme linked to the detection moiety (as in ELISA methods) .

If a detection moiety of a kit of the invention allows indirect detection of its target, the other reagents necessary for detection of the target (such as primary and secondary antibodies, chromogenic substrates) may be provided with the kit .

Preferably the label is a visually detectable label, such as a colour label, although other types of labels (such as luminescent or radioactive labels) may be used.

Detection of the different targets such that there is no indication of which target or targets have been detected may be achieved by labelling the different detection moieties with the same label . Capture of each target from the sample solution will then be indicated by the presence of the same label on the solid phase so that capture of one target is indistinguishable from capture of another target .

Alternatively, the different detection moieties may be labelled with different labels, but without informing the person performing the test or the person being tested which label represents detection of which target .

In some embodiments of the invention, it may be desired to provide different capture agents capable of binding the different targets . Each different capture agent comprises a capture ligand which can be bound by a capture moiety immobilised at a capture zone of the solid phase. The ligands of the different capture agents are of the same type, so that only a single type of capture moiety need be immobilised to the solid phase. The different capture agents are contacted with the sample solution so that target in the sample solution can bind to its capture agent. Each different target can then be captured on the solid phase by binding of the capture agent for that target to the capture moiety. Because the solid phase only comprises a single type of capture moiety, preparation of the solid phase is simplified.

In other embodiments of the invention, the solid phase may comprise a plurality of micro-particles wherein each target is capable of causing the micro-particles to agglutinate thereby indicating the presence of the target in the sample solution. Thus, if any of the targets are present . in the sample solution, the micro-particles will agglutinate. Because a positive result is indicated only by agglutination of the micro-particles, it is not possible to tell which target (s) has caused the agglutination.

This may be achieved by use of different capture moieties immobilised to the micro-particles. Different capture moieties should be capable of binding to different sites on each target, or to the same site present in multiple copies on the target, so that groups of micro-particles become cross-linked via the target, thereby causing agglutination of the micro-particles .

Preferred embodiments of the invention are now described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 which shows a nitrocellulose dipstick of a first preferred embodiment of the invention;

Figure 2 shows a nitrocellulose dipstick of a second preferred embodiment of the invention; and Figure 3 shows a multi-sided dipstick of a third preferred embodiment of the invention.

In figure 1, the nitrocellulose dipstick 10 has a contact end 12 for contacting a sample solution, a single capture zone 14 remote from the contact end, and a conjugate zone 16 between the contact end and the capture zone. A flow pad 18 is at the other end of the dipstick, and a control zone 19 is between the flow pad and the capture zone .

Four different capture moieties are immobilised at the capture zone. The different capture moieties are: HIV antigen, HCV antigen, HBV antibody, and Plasmodium antibody. Each of the four capture moieties is immobilised to a different thin strip (14a, b, c, d) of the capture zone. Adjacent capture moieties are contiguous with one another.

The following detection moieties are releasably immobilised to the conjugate zone 16 of the dipstick: i) colloidal gold labelled anti-human antibody, or colloidal gold labelled HIV antigen (to detect anti-HIV antibody target) ; ii) colloidal gold labelled anti-human antibody, or colloidal gold labelled HCV antigen (to detect anti-HCV antibody target) ; iii) colloidal gold labelled antibody to HBV (to detect HBV target) ; and iv) colloidal gold labelled Plasmodium antibody (to detect

Plasmodium target) .

To detect whether a person is infected with HIV, HBV, HCV, or Plasmodium, a blood, or plasma, or serum sample is collected from the person and is contacted with the contact end and conjugate zone of the dipstick in an undiluted or diluted form. The releasably immobilised detection moieties are solubilised by contact with the sample and bind to target (if present) in the sample. The sample passes up the dipstick by capillary action to the capture zone. If target is present in the sample, it should be bound by the appropriate detection moiety to form a complex which then passes up the dipstick to be captured at the capture zone. The presence of target in the sample is then indicated by accumulation of colour label at the capture zone of the dipstick. This is seen as a visible colour line.

The flow pad 18 absorbs sample solution which reaches it by capillary action. The control zone has a control moiety immobilised to it which is capable of binding directly to each of the different detection moieties to provide a positive control for the test. If a visible line appears at the control zone this confirms that sufficient amounts of the detection moieties have migrated through the dipstick membrane and are available for binding to the targets .

If a positive result is obtained at the capture zone, then because each different detection moiety has the same colour label, it is not possible to tell whether the person from which the sample has been obtained is infected with HIV,

HBV, HCV or Plasmodium. It is also not possible to tell which target (s) is present in the sample from the position in the capture zone at which the detection moiety accumulates because the strips of the capture zone are extremely thin and close together and cannot be distinguished visually. Thus, the person carrying out the test cannot identify to which strip (s) in the capture zone the detection moiety has bound.

The person can then be advised that their blood is not suitable for collection and transfusion and referred for further testing in the confidential environment of a hospital diagnostic or blood bank laboratory in order to establish which infection (s) the person has. It will be appreciated that the distress of public diagnosis of HIV infection is thereby avoided.

The further testing may be done for example by use of a dipstick having four separate lanes, each with a single capture zone, or by a single dipstick with four separate capture zones for specific detection of infection by HIV, HBV, HCV, and Plasmodium, respectively.

A dipstick for performing a test according to a second preferred embodiment of the invention is shown in Figure 2. The test is a triple screening test for markers of HCV, HIV and HBV infection to establish whether blood collected from a patient is suitable for transfusion. The sample solution is serum from venous blood.

The dipstick 20 has a contact end 22 for contacting the serum, a single capture zone 24 (in the form of a line across the dipstick) remote from the contact end, a control zone 26 further remote from the contact end, and a flow pad 28 at the other end of the dipstick. The flow pad absorbs sample solution which has passed through the dipstick by capillary action from the contact end.

The markers of viral infection are anti-HIV antibody, anti- HCV antibody, and HBsAg. Different capture moieties capable of binding the different markers are immobilised to the capture zone. The different capture moieties are immobilised to adjacent regions of the capture zone and are contiguous with each other.

To capture anti-HIV antibody, the capture moiety may comprise any of the following antigens : HIV core protein p24, the extra-cellular portion of gp41, or the extra- cellular portion of p31. Preferably a mixture of the antigens is used. One or more of the antigens can also be used as a detection moiety to detect captured anti-HIV antibody. Alternatively, the detection moiety may comprise an anti-human antibody capable of binding the anti-HIV antibody. In a further alternative arrangement, the capture moiety may comprise an anti-human antibody capable of binding the anti-HIV antibody and the detection moiety may comprise one or more of the above antigens . If it is desired to capture and detect anti-HIV 2 specific antibody this may be achieved using the extra-envelope, hydrophilic part of gp36. Although individuals infected with HIV-1 group 0 or group N are expected to cross-react with the above antigens, specific peptides can be used to improve antigenic reactivity of the capture.

To capture anti-HCV antibody, the capture moiety may comprise any of the following antigens: recombinant antigen corresponding to antigen of the NS3 or E2 region of HCV, a core peptide, or a peptide of the NS4 or Ξ2 region. Preferably a mixture of the antigens is used. One or more of the antigens can also be used as a detection moiety to detect captured anti-HCV antibody. Alternatively, the detection moiety may comprise an anti-human antibody capable of binding the anti-HCV antibody. In a further alternative arrangement, the capture moiety may comprise an anti-human antibody capable of binding the anti-HCV antibody and the detection moiety may comprise one or more of the above antigens .

To capture HBsAg, the capture moiety may comprise a monoclonal antibody to the ^λa' determinant of the S protein. Captured HBsAg can also be detected by a monoclonal antibody to the 'a' determinant of the S protein because this determinant is present in multiple copies in HBsAg. Alternatively, the capture moiety may comprise polyclonal antibody to HBsAg and the detection moiety a monoclonal antibody or an appropriate mixture of monoclonal antibodies to HBsAg, or vice versa .

Where the detection moiety for detecting anti-HIV antibody or anti-HCV antibody comprises an antigen, this is chemically linked to a universal tail comprising one or more ligands . Where the detection moiety for detecting any of the targets comprises an antibody, this is chemically coupled to one or more ligands. The ligand (s) of the detection moiety can be bound by a colour-labelled anti-ligand antibody (as a labelling agent) . For example, if the ligand is biotin, an anti-biotin antibody conjugated to colloidal gold or coloured latex particles may be used. The ligands allow the same labelling agent to be used to label each marker indirectly by binding to that marker's specific detection moiety.

To perform a test according to the second embodiment, the different detection moieties and the anti-biotin antibody conjugated to colloidal gold are mixed with a serum sample, The sample is then contacted with the contact end of the dipstick to allow sample to travel by capillary action through the capture and control lines of the dipstick. Sample which reaches the other end of the dipstick is absorbed by the flow pad.

If a viral marker is present in the sample, the specific detection moiety for that marker, bound to the anti-biotin colloidal gold conjugate should bind to the marker and the marker, detection moiety, and anti-biotin colloidal gold conjugate should be captured at the capture zone of the dipstick. Because there is only a single capture zone and the same colour line appears at the capture zone no matter which marker or markers are captured and detected, the test will only reveal that one or more of the viral markers is in the sample, but will not reveal which of the viral markers is present.

A moiety capable of binding directly to each of the different detection moieties ffor example an anti-biotin IgM antibody) is immobilised to the control zone to provide a positive control for the test. If a visible line appears at the control zone this confirms that sufficient amounts of the detection moieties and of the labelled anti-ligand antibody have migrated through the dipstick membrane and are available for binding to the markers .

The triple screening test of the second embodiment allows collected blood to be tested without anyone present, including the tester, being able to identify which viral marker (s) is responsible for a positive result. The confidentiality of the reason for the positive result is therefore preserved.

A third preferred embodiment of the invention is shown in figure 3. The figure shows a dipstick 30 comprising a closed tube of triangular cross-section. First 32, second 34, and third 36 sides of the dipstick are for capture and detection of a marker indicating infection by HIV, HCV, and HBV, respectively. The dipstick has a contact end 38 for contacting serum from venous blood and a flow pad 40 at the other end for absorbing serum which has passed to that end by capillary action. Each side has a capture line remote from the contact end, and a control line between the capture line and the flow pad. The capture lines of the different sides join to form a triangle around the dipstick, as do the control lines .

The markers of viral infection are anti-HIV antibody, anti- HCV antibody, and HBsAg. A capture moiety capable of binding anti-HIV antibody is immobilised to the capture zone of the first side of the dipstick. A capture moiety capable of binding anti-HCV antibody is immobilised to the capture zone of the second side of the dipstick. A capture moiety capable of binding HBsAg is immobilised to the capture zone of the third side of the dipstick. However, there is no indication of which markers are captured by the different sides of the dipstick.

Three different detection moieties are used to detect the viral markers . Each detection moiety is chemically linked to a biotinylated tail and is capable of specifically binding its viral marker. An anti-biotin antibody conjugated to colloidal gold is used to bind to the detection moieties to thereby allow indirect labelling of the targets.

To perform a test using the dipstick of the third embodiment, the detection moieties and the anti-biotin antibody conjugated to colloidal gold are mixed with a serum sample or plasma-containing sample. The sample is then contacted with the contact end of the dipstick to allow sample to travel by capillary action through the capture and control lines of each side of the dipstick. Sample which reaches the other end of the dipstick is absorbed by the flow pad.

If a viral marker is present in the sample, the specific detection moiety for that marker, bound to the anti-biotin colloidal gold conjugate should bind to the marker and the marker, detection moiety, and anti-biotin colloidal gold conjugate should be captured at the capture line of the side of the dipstick for that marker. Because there is no indication of which side of the dipstick captures each marker, and there is no visual difference between the different capture lines, the test will only reveal that one of the viral markers is in the sample, but will not reveal which of the viral markers is present .

A moiety similar to that described above for the second embodiment may be immobilised to the control lines to provide a check that the test is working properly.

Instead of being mixed with the sample solution, the detection moieties and/or the anti-biotin colloidal gold conjugate may be releasably immobilised to a conjugate zone of each side of the dipstick between the contact end and the capture zone of each side.

In other embodiments, the dipstick may have a different number of sides to allow capture and detection of a different number of targets. The dipstick may be of generally circular or oval cross-section, or cone shaped. The dipstick may be pyramid shaped (with a base and three or more sides, one side for each different target) . The tip of the cone or pyramid may form the contact end of the dipstick. In a further embodiment, the dipstick may comprise a disk with a central contact zone for contacting the sample solution, and different capture zones arranged radially around the contact zone. The different capture zones are substantially equidistant from the contact zone and substantially equally spaced from, or contiguous with each other. Different capture moieties capable of binding the different targets are immobilised to the different capture zones. Again, there is no indication of which target is captured at which capture zone so that capture and detection of a target using the dipstick does not reveal which target has been captured and detected.

Claims

1. A test for establishing whether any of a plurality of different targets are present in a sample solution which comprises contacting the sample solution with a solid phase to allow capture of target present in the sample solution by the solid phase, and establishing whether or not any of the targets has been captured, wherein a positive result is obtained if one or more of the targets are captured but does not indicate which target or targets have been captured.

2. A test according to claim 1 which comprises.- providing a solid phase having a plurality of different capture moieties immobilised thereto, each capture moiety being capable of capturing a different target; providing a plurality of different detection moieties, each detection moiety allowing detection of a different target captured by its capture moiety, detection of the different targets being such that there is no indication of which target or targets have been detected; contacting the solid phase with the sample solution to thereby allow capture of target by the capture moieties; and using the detection moieties to establish whether any of the different targets are captured from the sample solution.

3. A test according to claim 1 in which the solid phase comprises micro-particles and each different target is capable of causing the micro-particles to agglutinate thereby establishing that one or more targets have been captured without indicating which target or targets have been captured.

4. A test according to any preceding claim in which the sample solution is or is derived from a blood sample taken from a person and the test is for establishing whether the person' s blood is suitable for transfusion without disclosing why the blood is unsuitable for transfusion if a positive result is obtained.

5. A dipstick for establishing whether any of a plurality of different targets are present in a sample solution which comprises a plurality of different capture moieties each different capture moiety being immobilised to a different region of a capture zone of the dipstick and being capable of capturing a different target, wherein the different regions are not visually distinguishable.

6. A dipstick for establishing whether any of a plurality of different targets are present in a sample solution which comprises a capture zone to which a plurality of different capture moieties are immobilised, each different capture moiety being capable of capturing a different target, wherein the different capture moieties are interspersed with one another .

7. A multi-sided dipstick for establishing whether any of a plurality of different targets are present in a sample solution which comprises a different capture zone at each different side of the dipstick, a different capture moiety capable of binding a different target being immobilised at each different capture zone, wherein the different capture zones are at equivalent positions on each side of the dipstick so that if a target is captured and detected there is no indication of which target of the different targets has been captured and detected.

8. A dipstick according to any of claims 5 to 7 in which the dipstick comprises a contact end for contacting the sample solution and the dipstick is capable of transporting the sample solution by capillary action from the contact end to the capture zone or zones .

9. A dipstick for establishing whether any of a plurality of different targets are present in a sample solution which comprises a contact zone for contacting the sample solution and a plurality of different capture zones arranged radially around the contact zone substantially equidistant from the contact zone and substantially equally spaced from each other, a different capture moiety capable of binding a different target being immobilised to each capture zone and the dipstick being capable of transporting sample solution from the contact zone to the capture zones .

10. A kit for testing whether any of a plurality of different targets are present in a sample solution which comprises : i) a solid phase having a plurality of different capture moieties immobilised thereto, each different capture moiety being capable of capturing a different target; and ii) a plurality of different detection moieties, each different detection moiety allowing detection of a different target captured by its capture moiety; wherein a positive result is obtained if one or more of the different targets is captured and detected but there is no indication of which target or targets have been captured and detected.

11. A kit according to claim 10 in which the solid phase comprises a dipstick.

12. A kit according to claim 10 comprising a dipstick according to any of claims 5 to 9.

13. A kit according to claim 11 or 12 in which the plurality of different detection moieties are releasably immobilised to a conjugate zone of the dipstick between the contact end and the capture zone or capture zones .

14. A kit according to any of claims 11 to 13 in which each different detection moiety is provided with a ligand and the kit further comprises a labelling agent capable of binding the ligands of the different detection moieties, the labelling agent being labelled with a visible label .

15. A kit for testing whether any of a plurality of different targets are present in a sample solution which comprises : i) a solid phase having a capture moiety immobilised thereto; ii) a plurality of different capture agents, each different capture agent being capable of binding to a different target, and each different capture agent being provided with a ligand which can be bound by the capture moiety; and iii) a plurality of different detection moieties, each different detection moiety allowing detection of a different target captured via its capture agent by the capture moiety; wherein a positive result is obtained if one or more of the different targets is captured and detected but there is no indication of which target or targets have been captured and detected.

16. A test, dipstick or kit according to any preceding claim in which the different capture moieties are capable of capturing an antigen or nucleic acid of a micro-organism or infectious agent, or an antibody raised to an antigen of a microorganism or infectious agent .

17. A test, dipstick or kit according to any preceding claim in which the different capture moieties comprise or consist of any of the following: an HIV antigen; an HCV antigen; an antibody to HBV; and a Plasmodium antibody.

18. A dipstick or kit according to any of claims 5 to 17 for performing a test according to claim 4.

19. Apparatus for establishing whether any of a plurality of different targets are present in a sample solution which comprises a plurality of micro-particles wherein each different target is capable of causing the micro-particles to agglutinate so that agglutination occurs if one or more of the different targets are present in the sample solution.