Improvements relating to blood sampling devices

Abstract: A lancet has a needle (2) embedded in a plastics body (1), its tip (3) projecting from the forward end but being initially encased in a cap (4). This cap (4) is integrally moulded with the body, around the needle tip (3), and can be sheared away before use. The needle (2) can be pushed back in relation to the body (1) after use, conveniently by applying the cap (4) to the tip (3), until the tip is safely flush with, or set back with respect to, the leading end of the body (1). The rear end of the body (1) has a structure (9) to prevent the rear end of the needle (2) being pushed forwards again. To ensure that the tip disappears, the body (1) is formed with an intermediate, resiliently flexible bridge (17) stiff enough to remain rigid during pricking. But when the needle (2) is forced back and pressure is also applied to the part (18) of the body forward of the bridge (17), the needle (2) and that forward part (18) move back with respect to the rear part (19) of the body (1). Then the forward part (18) is released to move forwards, sprung by the bridge (17), leaving the needle (2) held by the rear part (19).

Description: This invention relates to blood sampling devices, and in particular to a lancet for pricking the skin to draw a small drop of blood for analysis. Such prickers are widely used by diabetics, for example, who need to know their sugar level. However, there are many other applications. There is an obvious need to make the sharp tip of the lancet safe after use. There have been various proposals for having the lancet as part of a cheap, disposable device which, after a single use, can be thrown away with the lancet automatically retracted inside the body and thus made safe. These are very handy, but in the long run it is more expensive to use them than to have a permanent firing mechanism and to load it when required with a lancet. But then the lancet must be made safe after removal. The usual form of lancet has a steel needle encased in an elongate plastics body. A cap is moulded integrally with this body and initially the tip of the needle is embedded in it. But the connection between the cap and the body is weak and the cap can be pulled free to expose the tip. After use, the cap may be used to cover the needle tip again, and it may be re-oriented to fit over the forward end of the body. The needle tends to be smooth and the plastics material of the body does not have much grip on it. It can happen that, when breaking the cap free, the cap is squeezed or angled with respect to the body sufficiently to pull the needle forwardly by its tip with respect to the body. There is then a lancet with a needle tip extending too far. There is also a trend towards making the needle thinner, to achieve an even sharper point, and therefore a less noticeable prick. But the needle also serves to give some strength to the lancet as a whole, providing a reinforcing rod along its axis. If it is too thin, the lancet is able to bend rather easily, and this is unsatisfactory. These problems have largely been answered by the lancet described in WO96/02189 which comprises a needle, an elongate body of moulded plastics material encasing most of the needle, and a breakaway cap integrally moulded with the body and initially encasing the tip of the needle. This is exposed at the forward end of the body when the cap is removed, and the needle is longitudinally movable rearwardly within the body to retract the needle tip after use. Thus, instead of trying to place the cap back over the end of the lancet after use, the needle is pushed backwards in relation to the body until the tip is flush with or recessed into the forward end. This pushing may be done using the original cap, which may be adapted for the operation. For example, the leading end of the body may be recessed, and the cap may have a projection which can enter the recess when pushing the tip of the needle. However, there is still uncertainty that the tip will always be retracted sufficiently. It is the aim of this invention to provide an even safer lancet. According to the present invention there is provided a lancet for a skin pricker comprising a needle with a tip and an elongate body of moulded plastics material encasing most of the needle, which is movable rearwardly with respect to the body to retract the needle tip within the body after use, the needle tip being initially encased by a breakaway cap integrally moulded with the body at its forward end to be exposed when the cap is removed, the mutual engagement of the needle and body being such that the needle cannot move forwards from its initial position relative to the body, and the needle and body remaining effectively integral and moving together during the act of skin pricking, characterised in that the body has a forward and rearward part joined by a bridge which acts as a spring normally holding the parts distanced but which is compressible to allow the parts to approach, the hold on the needle of the rearward part being greater than that of the forward part whereby, when the needle is pushed rearwardly with a pusher also acting on the forward part, the latter closes up towards the rearward part and the needle is retracted, and when the pusher is removed the rearward part holds the needle while the forward part is sprung forward by the bridge to shield the needle tip. Conveniently the bridge is provided by an aperture diametrally through the body, and this may be an enlargement of one of the apertures which are formed by elements which hold the needle while the body is moulded around it. Preferably the aperture is generally elliptical or lozenge shaped in cross section, the major axis of that section being transverse to the length of the body whereby in the normal, relaxed position, the ellipse or lozenge has a significant minor axis, but when the parts are pressed together this axis is reduced while the major axis slightly lengthens. The difference in hold may be achieved by different frictional grips, the rearward part being substantially longer than the forward part and thus having a much greater surface area in contact with the needle. Alternatively the hold on the needle of the rearward part may be a membrane at the rear end of the body against which the rear end of the needle bears during skin pricking, but which can be broken when the needle is urged rearwardly by a substantial force. A further option is for the hold on the needle of the rearward part to be a throat at the rear end of the body in which the rear end of the needle is trapped during skin pricking, but through which that rear end of the needle can be urged by a substantial force. Conveniently the cap is adapted to serve as an implement for pushing the tip of needle, after use, back into the body. The forward end of the body may be recessed and the cap may have a projection which can enter the recess when pushing the tip of the needle. Preferably, the rear end of the body is adapted to shield the rear end of the needle when the needle is retracted. The impediment to forward movement of the needle from its initial position relative to the body may be provided by a forwardly facing shoulder where the needle reduces in cross section to a leading length portion projecting from the body and terminating in the tip. The needle will generally be cylindrical with a flat formed over the leading length portion to make the reduced cross section. For a better understanding of the invention, one embodiment will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side view of a lancet prior to use, Figure 2 is a rear end view of the lancet, Figure 3 is a side view of the lancet with its needle being retracted after use, and Figure 4 is a side view of the lancet after retraction and ready to discard. The lancet has an elongate body 1 of moulded plastics material. It resembles the spool of a spool valve, having alternating large and small diameter sections. The three rearmost larger diameter portions have ribs to co-operate with the interior of the firing device and stop the body 1 rotating. Co-axially encased within the body 1 there is a needle 2 which projects in a sharp tip 3 at the forward end. This tip is initially encased in a cap 4 which is in the form of a disc with a central domed stud 5 on one face. The cap is integrally moulded with the body 1 and connects to it by a neck 6 which will be weak enough to be sheared off from the end surface 7 by a twisting action. The forward end of the body has a transverse recess 8 in which the surface 7 forms the base. At the other end, the body has a recess 9, initially empty but into which the rear end of the needle 2 projects when retracted. The needle 2 is cylindrical over most of its length, but at its forward end a flat 10 is formed which extends back from the extremity of the tip to a radial, semicircular shoulder 11. Thus far, the construction is very similar to that described in WO96/02189. However, there is a difference in the leading small diameter portion 12 of the body 1. Previously, this was recessed on one side and, in practice, had a diametrically opposed aperture on the other side as a result of the means which held the needle while the body 1 was moulded. There was a similar recess and aperture at the rear end. But these apertures were small and circular in cross section and the body remained substantially rigid. In this embodiment, there are still those recesses 13 and 14 and (disregarding the needle) the rear one 13 opens into a small circular aperture 15 as before. But the forward recess 14 opens into an enlarged aperture 16 whose cross section is substantially elliptical or lozenge shaped with the major axis transverse to the length of the body 1. This creates a narrow bridge 17 at each side dividing the body into a forward part 18 and a rearward part 19. In the normal, relaxed state as shown in Figure 1 the minor axis of the ellipse or lozenge is about two thirds the length of the major axis. For use, the cap 4 is twisted off and the lancet is fired in the usual way. Afterwards, the cap 4 may be used to press the needle to a retracted position, using the stud 5 as shown in Figure 3. As it is pressed against the needle tip 3, that will embed itself slightly, but the needle will be shifted rearwardly until the stud 5 meets the surface 7. Continued pressure, with the user holding the rearward part 19, forces the forward part 18 back and causes the aperture 16 to contract along its minor axis and expand slightly along its major axis as shown in Figure 3. Meanwhile, the rear end of the needle projects into the recess 9. The cap 4 is then removed, and the bridges 17, being of resilient plastics material, act as springs pushing the forward part 18 of the body 1 away from the rearward part 19 so that the body 1 resumes its original configuration. But a much greater length of needle 2 is within the rearward part 19 than the forward part 18, and the needle 2 is therefore held by the frictional grip of the rearward part 19 while the forward part 18 slides forwards relative to the tip 3, which is left concealed as shown in Figure 4. Instead of relying just on friction, as mentioned above there could be a membrane initially across the rear end of the needle which remains entire when pricking the skin, but which is broken when the needle is forced back after use. Alternatively, there might be a throat which the rear end of the needle only penetrates when forced back after use.

Claims: A lancet for a skin pricker comprising a needle (2) with a tip (3) and an elongate body (1) of moulded plastics material encasing most of the needle (2), which is movable rearwardly with respect to the body (1) to retract the needle tip (3) within the body (1) after use, the needle tip being initially encased by a breakaway cap (4) integrally moulded with the body (1) at its forward end to be exposed when the cap (4) is removed, the mutual engagement of the needle (2) and body (1) being such that the needle (2) cannot move forwards from its initial position relative to the body (1), and the needle (2) and body (1) remaining effectively integral and moving together during the act of skin pricking, characterised in that the body (1) has a forward (18) and rearward (19) part joined by a bridge (17) which acts as a spring normally holding the parts (18, 19) distanced but which is compressible to allow the parts (18, 19) to approach, the hold on the needle (2) of the rearward part (19) being greater than that of the forward part (18) whereby, when the needle (2) is pushed rearwardly with a pusher also acting on the forward part (18), the latter closes up towards the rearward part (19) and the needle (2) is retracted, and when the pusher is removed the rearward part (19) holds the needle (2) while the forward part (18) is sprung forward by the bridge (17) to shield the needle tip (3). A lancet as claimed in Claim 1, characterised in that the bridge (17) is provided by an aperture (16) diametrally through the body (1). A lancet as claimed in Claim 2, characterised in that the diametral aperture (16) is an enlargement of one of the apertures which are formed by elements which hold the needle (2) while the body (1) is moulded around it. A lancet as claimed in Claim 2 or 3, wherein the aperture (16) is generally elliptical or lozenge shaped in cross section, the major axis of that section being transverse to the length of the body (1) whereby in the normal, relaxed position, the ellipse or lozenge has a significant minor axis, but when the parts are pressed together this axis is reduced while the major axis slightly lengthens. A lancet as claimed in any preceding Claim, characterised in that the difference in hold is achieved by different frictional grips, the rearward part (19) being substantially longer than the forward part (18) and thus having a much greater surface area in contact with the needle (2). A lancet as claimed in any one of Claims 1 to 4, characterised in that the hold on the needle (2) of the rearward part (19) is a membrane at the rear end of the body (1) against which the rear end of the needle (2) bears during skin pricking, but which can be broken when the needle (2) is urged rearwardly by a substantial force. A lancet as claimed in any one of Claims 1 to 4, characterised in that the hold on the needle (2) of the rearward part (19) is a throat at the rear end of the body in which the rear end of the needle (2) is trapped during skin pricking, but through which that rear end of the needle (2) can be urged by a substantial force. A lancet as claimed in any preceding Claim, characterised in that the cap (4) is adapted to serve as an implement for pushing the tip (3) of the needle (2), after use, back into the body (1). A lancet as claimed in Claim 8, characterised in that the forward end of the body (1) is recessed and the cap (4) has a projection (5) which can enter the recess (8) when pushing the tip (3) of the needle (2). A lancet as claimed in any preceding Claim, characterised in that the rear end of the body (1) is adapted to shield the rear end of the needle (2) when the needle (2) is retracted. A lancet as claimed in any preceding Claim, characterised in that the impediment to forward movement of the needle (2) from its initial position relative to the body (1) is a forwardly facing shoulder (11) where the needle (2) reduces in cross section to a leading length portion projecting from the body and terminating in the tip (3). A lancet as claimed in Claim 11, characterised in that the needle (2) is generally cylindrical with a flat (10) formed over the leading length portion to make the reduced cross section.

Inventors: MARSHALL JEREMY, MARSHALL, JEREMY
Applicants: OWEN MUMFORD LTD, OWEN MUMFORD LIMITED
Application year: 1997
Main classification: A61B5
IPC codes: A61B5