CA2602719A1

CA2602719A1 - Method and device for the extraction of a body fluid

Info

Publication number: CA2602719A1
Application number: CA002602719A
Authority: CA
Inventors: Heinz-Michael Hein; Reto Abt; Stephan Korner; Irio Giuseppe Calasso; Emad Sarofim; Patrick Griss; Rainer Jaeggi
Original assignee: Individual
Current assignee: F Hoffmann La Roche AG
Priority date: 2005-04-07
Filing date: 2006-04-06
Publication date: 2006-10-12
Anticipated expiration: 2026-04-06
Also published as: WO2006105968A1; ES2332146T3; ATE446049T1; US20110028862A1; PL1868500T3; US7833172B2; EP1868500A1; EP1868500B1; EP2140811A1; CN101816563A; EP2140811B1; ES2400871T3; HK1147668A1; CN101816563B; EP1709906A1; CA2602719C; CN101155550B; PL2140811T3; JP2008534192A; US20080108910A1

Abstract

The invention relates to a method and a device for the extraction of a body fluid, whereby a piercing element (10) is inserted, by way of an advance movement (54), through the skin into a body part (14) and the body fluid is received via a capillary structure (18) of the piercing element (10). The invention is characterized by detecting any contact of the piercing element (10) with body fluid after the advance movement (54) and during a collection phase (62) inside the body part (14).

Description

Method and device for the extraction of a body fluid Description The invention concerns a method for withdrawing body fluid and in particular blood in which a lancing element is inserted through the skin into a body part in a forward movement and the body fluid is taken up by a capillary structure of the lancing element. The invention also concerns a corresponding device.

Such methods and withdrawal devices for small amounts of body fluids are used above all by diabetics for the self-monitoring of blood sugar which is carried out several times daily. Recent concepts envisage a measuring microneedle as a disposable in a hand-held device to generate a skin puncture, to remove a small amount of blood therefrom utilizing capillary forces and to analyse this blood sample. With such an integrated system it should be possible for even laymen to simply and rapidly carry out the necessary steps in a substantially automated measuring process. In order to achieve this it is important that on the instrument side the lancing and collecting process are adapted to the disposable in order that blood or optionally tissue fluid can be collected efficiently, rapidly and free of pain.
In this connection it has already been suggested to detect a skin contact in order to thus be able to achieve a defined lancing depth for the control of the forward-directed lancing movement. However, such a movement control has to be adapted to the desired high lancing speed using very complex apparatus. However, it is especially disadvantageous that it cannot be used to give information about the actual success of the blood collection.

In order to optimize blood collection, WO 03/009759 Al of the applicant describes a combination method in which firstly a puncture is made, the lancing unit with a capillary structure is then pulled back along a part of the lancing path and is left there for a collecting period of a few seconds. This should release a part of the lancing channel such that body fluid can collect therein and from there can enter the capillary structure.

A lancing system is known from W02004/080306 which is designed to detect a characteristic parameter (e.g. impedance) during the lancing movement and optionally also during the retraction. However, this should only serve as a skin detection as such in order to optionally indicate the penetration depth or penetration stability or residence time for the user. In contrast a check of the success of an actual liquid contact beyond the skin detection is not mentioned anywhere.

On this basis the object of the invention is to avoid the disadvantages that occur in the prior art and to enable an optimized collection of body fluid especially with regard to reliability, efficiency, pain minimization and hygiene while being simple to use.

The combination of features stated in the independent patent claims are proposed to achieve this object.

The invention is based on the idea of enabling a check of the success of the liquid collection instead of a lancing check in a subsequent phase of blood collection.
Accordingly with regard to the process it is proposed that a contact of the lancing element with body fluid is detected after the forward movement during a collection phase inside the body part. Correspondingly a detection means is provided for a device to detect a contact of the lancing element with body fluid after the forward movement during a collection phase inside the body part. In this manner it is possible to optimize the withdrawal because when liquid contact has been detected, there must certainly have been an afterflow of body fluid from the puncture wound.
This enables a process that is appropriate to the situation which also takes into account user-specific parameters such as local skin condition and blood circulation.
The reliability with regard to the minimum required amount of blood for a test is increased and a pain-minimized withdrawal is possible because the duration can be adapted depending on the liquid contact event.

Another aspect of the invention is to not carry out the collection process statically but rather to ensure an improved inflow of blood in a reduced-pain zone.
Accordingly a method is proposed in which after the forward movement, the lancing element is retracted by a first distance in a retraction phase and by a second distance in a later collection phase, wherein the retraction phase is shorter than the collection phase and the first distance is larger than the second distance and the second distance is larger than zero. A corresponding device provides that the lancing drive is designed to move the lancing element back by a first distance in a retraction phase and by a second distance in a later collection phase, wherein the retraction phase is shorter than the collection phase and the first distance is larger than the second distance and the second distance is larger than zero. This allows a lancing channel to be created in a blood zone in a rapid and pain-reduced manner while the collection process takes place for the period required to self-transport the liquid in the capillary structure in a less sensitive outer skin zone. Surprisingly it has turned out that the slow retraction results in a considerably improved collecting efficiency than is the case for static collecting positions. One possible explanation for this is that after the rapid lancing movement the skin is pushed in by the lancing member and this pressing force initially prevents the flow of blood. However, the skin relaxes again during the slow retraction during the collection phase so that blood can flow back in in an improved manner. It is also conceivable that a type of suction effect is achieved by the retraction of the lancing element so that additional blood is available. In this connection collection in the lanced state is hygienically favourable and efficient for a metered withdrawal of small amounts of liquid.

Advantageous embodiments and further developments are derived from the dependent claims.

The pain region of the body part or of the skin is rapidly exited as a result of the rapid backward movement into a retraction position of lower puncture depth.
After a waiting period it is then checked whether further blood flows in via the lancing channel in this outer non-blood-delivering zone. When there is liquid contact it can be assumed that there is a high collection success rate without an excess dead volume. In addition liquid can be collected particularly hygienically while still in the skin without any visible escaping blood. A measurement of impedance with incorporation of the lancing member as an electrode is especially suitable for detecting the liquid contact. It can be checked whether body fluid has been received from the body part or from the puncture wound on the basis of a detected contact with body fluid. The probability that the liquid has been successfully collected is considerably increased by such a check. This also allows one to wait for the optimal collection period. Optionally an error signal is generated in the absence of a contact and the collection process is discontinued.

After the rapid retraction of the lancing element, the body fluid is particularly preferably taken up during a collection phase in the outer painless skin layer. In this process the lancing element is steadily retracted or retracted at a variable speed at least during a part of the collection phase which considerably improves the collecting efficiency. The collection time should be sufficient to ensure an adequate uptake of liquid under the capillary action.

In particular all disclosed embodiments can be combined with one another with regard to the detection of body fluid and the lancing profiles.

The invention is further elucidated in the following on the basis of the embodiment examples shown schematically in the drawing.

Fig. 1 shows a block diagram of a device for withdrawing and optionally for analysing blood from a body part.

Figs. 2 to 5 show a lancing element of the device according to fig. 1 in various lancing positions in a simplified sectional view.

Figs. 6 to 9 show various lancing profiles when using the lancing element.
Fig. 10 shows the anatomy of human skin in a diagrammatic view.

Fig. 11 shows the signal time course in various constellations of a body fluid contact.

The device shown in the drawing is for the self-withdrawal of a blood sample by a user for analytical purposes and in particular for blood sugar monitoring. The device comprises a lancing element 10 as a disposable article for blood collection and a hand-held device 12 for automatically handling the lancing element 10 that is used.
The lancing element 10 shown in fig. 1 is designed as a so-called "microsampler"
for collecting a small amount of blood from a body part 14 and in particular from a fingertip. It is a flat shaped member made of thin high-grade steel sheet and has a distal shaped tip 16 as a lancing member which is connected via a semi-open groove-shaped capillary channel 18 to a collection site 20 which can be designed as a reaction area for detecting an analyte e.g. glucose. The detection of blood glucose in particular by means of contact-free optical methods is known in the prior art and is therefore not elucidated in more detail here. Optionally the collected blood can also be transferred into an analytical unit in order to determine the analyte there.

The device or instrument 12 has a lancing drive 22 for a controlled forward and backward movement of the lancing element 10 and it has detection means 24 for detecting a contact of the lancing element 10 with blood during a collection phase.
The lancing drive 22 comprises a mechanical and/or electrical drive unit 26 which is coupled to the lancing element 10. In particular a two-step hybrid drive can be provided in which a rapid movement is undertaken by a mechanism for example a drive spring or drive guide block whereas a slower controlled movement is carried out by an electric motor. Alternatively the lancing stroke can also be effected by an electromagnetic drive like the coil of a loudspeaker. The lancing drive 22 additionally comprises a control unit 28 to control or regulate the process of blood withdrawal and in particular the lancing movement. It is expedient to use a microcontroller for this purpose which can optionally be user-specifically parameterized.

The detection means 24 can detect the contact with blood during the collection phase by means of a measurement of impedance by the lancing member 16 and a pressure ring 30 as a counter-electrode which is axially penetrated by the lancing member and is in contact with the body part 14. In this connection the lancing member consisting of electrically conductive material can be safely actuated by an electrical alternating voltage signal e.g. 4 Vpp and 10 kHz in which case the impedance in the path between the lancing member and counter-electrode is significantly decreased by a fluidic contact. A control device 32 enables a the success of blood collection to be checked depending on the detected liquid contact as further elucidated in the following.

Figs. 2 to 5 illustrate the process of blood collection by means of the lancing element 10. Firstly the lancing member 16 is inserted in a distally-directed forward movement through the skin surface 34 into the body part 14 to a predetermined depth such that a blood-delivering zone 36 in the dermis is reached. The blood capillaries which can be opened by the lancing member, end in this region.

However, at the same time the pain sensation in this deeper region 36 is high due to the nerve cells that are present there. For this reason it is advantageous when the lancing element is pulled back in a retraction movement from the deepest puncture position 38 into a retraction position 40 of lesser lancing depth immediately after the forward movement (fig. 3). This retraction position is preferably in the region of the epidermis 42 and in particular in the stratum comeum 44. A certain time elapses after the rapid retraction of the lancing element 10 until the blood 46 flows back into the epidermis through the puncture channe148 that has been generated.

The dimensions of the layer structure of human skin are realistically illustrated in fig. 10. The epidermis with the stratum comeum as the uppermost skin layer has a depth of about 0.5 to 1 mm whereas the dermis containing the blood capillaries extends into a depth range of a few millimetres.

According to fig. 4 blood contact is detected in the retracted collecting position 40 by the detection means 24 as a check of success after a waiting period after the forward movement. This allows the collection time to be optimized because if there is contact with liquid, blood has certainly subsequently flowed from the puncture wound. If, in contrast, no contact with blood has been detected after the waiting period, the measurement can be discontinued by the control device 32. This results in no false results due to the absence of a blood volume or a blood volume that is too small. Expediently the control device 32 gives the user a corresponding signal.
The collection process does not have to be carried out statically but instead can be carried out in the course of a further backward movement of the lancing element 10.
Optionally a collection on the skin surface 34 is also possible as shown in fig. 5. In this case contact with liquid can be reliably detected by the lancing member 16 as a measuring electrode which dips into an escaped drop of blood 50 and is thus in fluidic contact with the skin, and by the pressure ring 30 resting against the skin as a counter-electrode. The pressure ring is additionally intended to support the blood flow under pressure and to open the wound so that the contact between the lancing member and skin and thus the pain for the user is minimal.

The lancing profiles shown in figs. 6 to 9 are particularly advantageous for collecting blood in a manner that is as successful and pain-free as possible.
In this connection the term lancing profile is to be understood as the time course of the lancing movement plotted as a function of lancing depth versus time.

In the lancing profile shown in fig. 6 the lancing member is rapidly inserted in a forward movement 54 to a predetermined depth 56 into the blood-delivering, pain-sensitive skin region 52 and immediately retracted in a retraction movement 58 up to a depth of about 0.5 mm. The retraction phase is of the same order of magnitude as the duration of the forward movement i.e. a few 100 s. The retraction position 60 can be located in the region of the stratum corneum and thus outside of the pain region 52. A collection phase 62 occurs subsequently in which blood is collected while the lancing element is slowly pulled back until it reaches the skin surface.
This collection phase 62 lasts a few seconds whereby the distance d2 travelled by the lancing member is substantially smaller than the retraction distance dl during the retraction phase 58. As a result of the subsequent slower retraction, the skin relaxes so that the lancing channel does not immediately become blocked again.
Since the collection process requires a certain amount time, it is expediently carried out in the nerve-free outer skin zone. The collection under the skin surface i.e. in the lanced state is also important in order to avoid blood discharge onto the skin and thus to enable a particularly hygienic withdrawal process. Furthermore, blood which has already discharged onto the skin surface can only be cleanly removed with the lancing element 10 when the capillary force of the capillary 18 is large enough at this position. This is the case when the lancing member 16 is at least in a slightly inserted state because the capillary depth becomes smaller towards the tip and thus the capillary force also decreases.

Electrical or electromagnetic drives are more suitable than purely mechanical drives for the lancing profile according to fig. 6 because in the latter case bouncing effects are more difficult to control (a damping action can be more simply achieved by electrical means compared to a mechanical solution.

In order to be able to adjust the lancing depth in a defined manner, the skin surface can for example be detected by an impedance measurement before the actual lancing process. In this case the position of the skin surface can be detected during a slow forward movement of the lancing element 10.

The switching between the various regions of the lancing profile can either be controlled by the position (depth) or be time-controlled. The transition between the regions with different speeds can occur by a discontinuous change or it can be a fluid transition (continuous change in speed). The continuous movement has the advantage that less drive energy is required and the control of the movement is simplified.

The lancing profile shown in fig. 7 differs only by an additional step 64 during the collection phase 62. In this case after the rapid retraction to depth B, there is a somewhat slower retraction to depth C and the skin relaxes during this interval. The actual collection process then occurs at an even slower speed from depth C to the skin surface. This enables a shortening of the entire lancing and collecting process.

A similar embodiment is provided according to fig. 8 in which after the rapid retraction phase 58, the skin relaxation is achieved by a slow retraction of the lancing member until time tl, and subsequently collection is continued until time t2 while the lancing member is at rest. In this case a lateral displacement of the lancing member relative to the skin can be clearly felt by the user.

In the lancing profile according to fig. 9 the lancing member is completely pulled back out of the skin after a first rapid forward movement 54 and subsequently lanced again to a lesser lancing depth in a second forward movement 54'. At this point a blood contact is then detected and subsequently the collection process 62 is carried out while slowly retracting the lancing member until it reaches the skin surface. The advantage of the complete retraction is that any after-bouncing of the lancing member takes place outside of the skin and thus no damping is required which greatly reduces the demands on the actuatorics.

This lancing profile lends itself to a simple control variant. Initially the skin surface can be detected before time tO in order to accurately determine the lancing depth.
This process could be carried out inductively or by an impedance measurement, by slowly moving the lancing element towards the skin until its surface is touched as described above. The first lancing process (rapidly in and rapidly out) can then immediately take place in an uncontrolled manner i.e. without feedback by a control circuit. This has the advantage, especially when an electromagnetic coil drive is used, that it is possible to obviate the use of rapid and expensive control electronics.
In the case of a hybrid drive this rapid lancing process would be performed by the mechanical part (e.g. spring drive or guide block drive). After the first lancing action the lancing member is moved forward more slowly than previously (phase 54'). This movement can also take place without a control loop. Once the skin surface is reached (optionally detected by renewed skin detection), a control signal can be triggered which triggers the remaining section of the lancing profile (collection phase). The reversal point 66 can be determined relative to the trigger signal by a time delay. This time delay must be short enough in order to not penetrate again into the pain zone 52. The collection process until t2 can then also take place by a simple control also without position control. Afterwards the lancing element is retracted into the device until time t3 and thus the lancing member is removed from the skin.

The time course of the measurement signal 68 is shown in more detail for various methods of blood contact in the configuration according to figs. 2 to 4. When dry skin is penetrated the conductivity at first decreases more slowly up to a bending point 70, until the tip 16 making contact with blood in the dermis 36 leads to a rapid increase in the signal. A signal level 72 is reached at the end of the forward movement which is characteristic for a direct liquid contact and can thus serve as a reference signal. In this connection it should be noted that when contact is made with the skin it is initially the conductivity or impedance of the skin area between the tip 16 and the ring electrode 30 and thus the ring radius which is relevant. When the tip 16 dips into the body fluid 16, the effective electrode area increases abruptly and the signal is only influenced by the thickness of the skin layer between the blood zone 36 and the ring 30 resting thereon which is substantially less than the ring radius. Hence especially when measuring capacitance it is advantageous when the ring 30 is electrically insulated from the skin surface 44.

Thus according to fig. 11 a the end of the forward movement at which the blood-delivering zone 36 is reached according to fig. 2, a signal level 72 is attained which is characteristic (and can optionally be determined empirically) for a liquid contact.
During the subsequent retraction into the collecting position 40 according to fig. 3 it may be the case that a short time elapses before the body fluid has flowed back up to the retracted needle tip. Accordingly the signal decreases during retraction and again reaches the maximum value 72 at the second contact with blood. Thus after a predetermined waiting time it is possible to check the success of blood collection by making a comparison to determine whether the high signal level is again present.

If there is a rapid after-flow of body fluid, the liquid contact with the retracted tip 16 is not disrupted and the signal level remains constantly high as shown in fig.
11 b.
Also in this case a positive check of success is possible.

In contrast according to fig. 11 c there is no or only a poor after-flow of blood and the signal level further decreases even in the retracted position so that a fault is detected after a defined waiting period on the basis of the change of the measurement signal in which case a collection of body fluid has probably not been successful. A critical change in the signal can be determined by a comparison with the signal level at the start of the waiting period or by evaluating the slope of the signal time-course. As a result the measurement can then be terminated and the user can be warned.

Claims

1. Method for withdrawing body fluid, in particular blood in which a lancing element (10) is inserted through the skin into a body part (14) in a forward movement (54) and the body fluid is taken up by a capillary structure (18) of the lancing element (10), characterized in that a contact of the lancing element (10) with body fluid is detected after the forward movement (54) during a collection phase (62) inside the body part (14).

2. Method according to claim 1, characterized in that after the forward movement (54), the lancing element (10) is pulled back in a retraction movement from the deepest lancing position into a retraction position (60) of lesser lancing depth.

3. Method according to claim 2, characterized in that the contact with body fluid is detected in the retraction position (60).

4. Method according to one of the claims 1 to 3, characterized in that contact with body fluid is detected by a measurement signal at the beginning and at the end of a waiting period after the forward movement (54) in order to check that it has been successful, wherein a given change in signal is identified as a fault.

5. Method according to one of the claims 1 to 4, characterized in that the lancing element (10) is retracted from the skin after a first forward movement (54) and immediately inserted again with less lancing depth in a second forward movement (54'), and that subsequently contact with a body liquid is detected.

6. Method according to claim 5, characterized in that the contact with body fluid is detected during the renewed insertion at the point of reversal (66) into a retraction movement.

7. Method according to one of the claims 1 to 6, characterized in that the contact with body fluid is detected in the region of an outer skin layer (42), preerably in the region of the stratum corneum (44).

8. Method according to one of the claims 1 to 7, characterized in that the body fluid is collected in a skin layer of the body part (14) that is not supplied with blood or weakly supplied with blood.

9. Method according to one of the claims 1 to 8, characterized in that the body fluid is collected via the lancing channel (48) which is vacated when the lancing element (10) is retracted where said lancing channel (48) acts as a connection to a blood-delivering zone (36) of the body part (14).

10. Method according to one of the claims 1 to 9, characterized in that at least an aliquot of the body fluid on the skin is collected outside of the body part (14).

11. Method according to one of the claims 1 to 10, characterized in that the contact with body fluid is detected by the lancing element (10) and a preferably electrically insulated contact element (30) which is in contact with the body part (14).

12. Method according to one of the claims 1 to 11, characterized in that the contact with body fluid is detected by an electrical measurement parameter in particular capacitance or inductance or resistance.

13. Method according to one of the claims 1 to 12, characterized in that the contact with body fluid is detected by the lancing element (10) by means of an impedance measurement relative to the skin.

14. Method according to one of the claims 1 to 11, characterized in that the contact with body fluid is optically detected within the body part (14) preferably through the capillary structure (18) or through a light guide.

15. Method according to one of the claims 1 to 14, characterized in that the successful collection of a sample of body fluid is checked by detecting the contact with body fluid.

16. Method according to one of the claims 1 to 15, characterized in that while contact with body fluid is detected a predetermined collection period for collecting the body fluid is allowed to elapse and subsequently the lancing element (10) is completely retracted from the body part (14).

17. Method according to one of the claims 1 to 16, characterized in that in the absence of contact with body fluid an error signal is generated and the withdrawal process is terminated.

18. Method for withdrawing body fluid, in particular blood in which a lancing element (10) is inserted through the skin into a body part (14) in a forward movement (54) and the body fluid is taken up by a capillary structure (18) of the lancing element (10), characterized in that after the forward movement (54) the lancing element (10) is retracted by a first distance (d1) in a retraction phase (58) and by a second distance (d2) in a later collection phase (62), wherein the retraction phase (58) is shorter than the collection phase (62) and the first distance (d1) is larger than the second distance (d2) and the second distance is larger than zero.

19. Method according to one of the claims 1 to 18, characterized in that the body fluid is collected essentially during the collection phase (62).

20. Method according to claim 18 or 19, characterized in that the duration of the retraction phase (58) is selected to be of the same order of magnitude as the duration of the forward movement (54).

21. Method according to one of the claims 18 to 20, characterized in that the collection phase (62) is 10- to 10,000-fold longer than the retraction phase (58).

22. Method according to one of the claims 1 to 21, characterized in that the lancing element (10) is retracted during the collection phase (62) preferably at a uniform speed.

23. Method according to one of the claims 1 to 21, characterized in that the lancing element (10) is retracted more rapidly in a first time segment of the collection phase (62) compared to a subsequent time segment.

24. Method according to claim 23, characterized in that the lancing element (10) is stopped for a certain holding time in the second time segment.

25. Method according to one of the claims 18 to 24, characterized in that the lancing element (10) is completely pulled out of the skin in the retraction phase (58) and again inserted to a lesser lancing depth before the collection phase (62).

26. Method according to one of the claims 18 to 25, characterized in that the lancing element (10) is moved back by a second distance of between 2 mm and 0.1 mm during the collection phase (62).

27. Method according to one of the claims 1 to 26, characterized in that the lancing element (10) is pulled back into the region of the stratum corneum (44) during the collection phase (62).

28. Method according to one of the claims 1 to 27, characterized in that the movement of the lancing element (10) is controlled by a registration of time or position.

29. Device for withdrawing body fluid and in particular blood comprising a lancing element (10) for insertion through the skin into a body part (14) and having a capillary structure (18) to collect the body fluid, and a lancing drive (22) for a forward and backward movement of the lancing element (10) characterized by a detection means (24) which detects contact of the lancing element (10) with body fluid by a measurement signal during a collection phase (62) at least at the beginning and at the end of a waiting period after the forward movement (54) in order to check that it has been successful.

30. Device according to claim 29, characterized in that after the forward movement (54), the lancing element (10) can be pulled back in a retraction movement out of the deepest lancing position into a retraction position of lesser lancing depth by means of the lancing drive (22), and that the detection means (24) responds when there is a contact with body fluid in the retraction position.

31. Device according to claim 29 or 30, characterized in that contact with body fluid is detected after the forward movement (54) preferably within the body part (14) wherein a given change in signal is identified as a fault.

32. Device according to one of the claims 29 to 31, characterized in that the lancing drive (22) is designed to retract the lancing element (10) from the skin after a first forward movement (54) and to immediately insert it again in a second forward movement (54) of lesser lancing depth, and that subsequently the detection means (24) responds when there is contact with body fluid.

33. Device according to one of the claims 29 to 32, characterized in that the lancing drive (22) is designed in two stages wherein a first drive stage which preferably operates mechanically is provided for a rapid movement and a second drive stage which preferably operates electrically is provided for a slower controlled movement of the lancing element (10).

34. Device according to one of the claims 29 to 33, characterized in that contact with body fluid can be detected by the lancing element (10) and a preferably electrically insulated contact element (30) which is in contact with the body part (14).

35. Device according to one of the claims 29 to 34, characterized by electrodes (10, 30) as detection means for detecting a contact of the lancing element (10) with body fluid on the skin outside of the body part (14) wherein the electrodes are formed by the lancing element (10) which is in fluidic contact with the skin via the body fluid and a contact element (30) which is in contact with the skin.

36. Device according to one of the claims 29 to 35, characterized in that the detection means (10, 30, 24) detect the contact with body fluid when a signal level that is optionally determined empirically of an electrical measurement parameter and in particular capacitance or inductance or resistance is reached.

37. Device according to one of the claims 29 to 36, characterized in that the contact with body fluid can be detected by the lancing element (10) by an impedance measurement relative to the skin.

38. Device according to one of the claims 29 to 33, characterized in that the contact with body fluid can be detected by optical detection means within the body part (14) preferably through the capillary structure (18) or through a light guide.

39. Device according to one of the claims 29 to 38, characterized by a control device (32) for checking the success of liquid collection according to the detected contact with body fluid.

40. Device according to claim 39, characterized in that the control device (32) generates an error signal and terminates the withdrawal process in the absence of a contact with body fluid.

41. Device for withdrawing body fluid and in particular blood comprising a lancing element (10) for insertion through the skin into a body part (14) and having a capillary structure (18) to collect the body fluid, and a lancing drive (22) for a forward and backward movement of the lancing element (10) characterized in that the lancing drive (22) is designed to move the lancing element (10) back by a first distance (d1) in a retraction phase (58) and by a second distance (d2) in a later collection phase (62), wherein the retraction phase (58) is shorter than the collection phase (62) and the first distance (d1) is larger than the second distance (d2) and the second distance is larger than zero.

42. Device according to claim 41, characterized in that the duration of the retraction phase (58) is of the same order of magnitude as the duration of the forward movement (54).

43. Device according to claim 41 or 42, characterized in that the collection phase (62) is 10- to 10,000-fold longer than the retraction phase (58).

44. Device according to one of the claims 29 to 43, characterized in that the lancing drive (22) retracts the lancing element (10) during the collection phase (62) preferably at a uniform speed.

45. Device according to one of the claims 29 to 43, characterized in that the lancing drive (22) retracts the lancing element (10) more rapidly in a first time segment of the collection phase (62) compared to a subsequent second time segment.

46. Device according to one of the claims 29 to 43, characterized in that the lancing drive (22) stops the lancing element (10) in the second time segment for a certain holding time.

47. Device according to one of the claims 41 to 46, characterized in that the lancing drive (22) completely pulls the lancing element (10) out of the skin during the retraction phase (58) and inserts it again to a lesser lancing depth before the collection phase (62).

48. Device according to one of the claims 41 to 47, characterized in that the lancing element (10) is moved back by the lancing drive (22) by a second distance of between 2 mm and 0.1 mm during the collection phase (62).

49. Device according to one of the claims 29 to 48, characterized in that the movement of the lancing element (10) is controlled by a registration of time or position.