Abstract:
An apparatus for collecting a body fluid for testing for an analyte includes a needle for penetrating a patient&#39;s skin to access the fluid within the skin. The needle has a hollow body extending from a first end to a second end. An interior surface of the body defines a fluid pathway extending between the ends. The second end is positioned to deposit fluid for testing. The first end has a beveled face on a front side of the body. The beveled face terminates at a penetration tip with the beveled face having an opening in communication with the fluid pathway. The penetration tip is burnished to a rounded shape and bent to facilitate low pain and rapid fluid collection.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation-in-part of U.S. patent application Ser. No. 09/244,952 filed Feb. 4, 1999, now abandoned the disclosure of which is hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This invention pertains to testing a body fluid for an analyte. More specifically, the present invention pertains to a novel needle design in combination with a collection apparatus for collecting a sample of such a fluid. 
     BACKGROUND 
     Numerous patents teach various ways for collecting a sample of body fluid and testing such fluid for an analyte such as glucose. For example, U.S. Pat. Nos. 5,820,570 and 5,823,973 describe methods and apparatus for obtaining, in one embodiment, interstitial fluid which is tested for glucose through IR absorption. These patents also describe use of the disclosed inventions in colormetric and electro-chemical testing of glucose. 
     Present development efforts are directed to testing very small volumes of body fluid (e.g. about 0.5 μl). The use of such small volumes of fluid permits less painful collection of a fluid samples. However, small fluid volumes present additional challenges for analyte testing. For example, testing for analytes typically requires a fluid sample in excess of a predetermined minimum volume. By way of non-limiting representative example, a test may require a minimum sample size of about 1 to 5 μl to yield reliable test results. 
     The &#39;973 patent shows a small diameter needle (about 28 to 32 gauge or about 0.36 mm to 0.23 mm outside diameter) with a length to penetrate into but not through a dermis to access interstitial fluid contained within the dermis. Preferably, the fluid is blood-free to facilitate subsequent testing of the fluid for analytes such as glucose. 
     The use of a small needle dimensioned as described in the &#39;973 patent greatly reduces pain. However, pain may occasionally occur. Further, there is a need for a needle design that enhances the rate at which a sample is collected by such a needle. 
     SUMMARY 
     The present invention is directed to an apparatus for collecting a body fluid for testing for an analyte contained within said body fluid. The apparatus comprises a needle for penetrating a patient&#39;s skin to access the fluid within said skin. The needle has a hollow body extending from a first end to a second end with a fluid pathway extending between the ends. The second end is positioned to deposit fluid for testing. The first end is configured to penetrate the skin and includes a beveled face on a front side of said body. The beveled face terminates at a penetration tip. The beveled face has an opening in communication with the fluid pathway. The body has a linear axis adjacent the first end. The first end includes a bend formed on the front side of the beveled face to be deflected toward said front side. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation view of a needle contained in a sampler; 
     FIG. 2 is a side sectional view of a needle positioned relative to an absorbent membrane; 
     FIG. 3 is a side elevation view of a needle being bent; 
     FIG. 4 is a top plan view of a bent needle; 
     FIG. 5 is a view taken along line  5 — 5  of FIG. 4; 
     FIG. 5A is an end view of a discharge end of a bent needle; 
     FIG. 5B is a view taken along lines  5 B— 5 B of FIG.  5 A and providing an enlarged view of a bent tip of the needle of FIG.  5  and showing a preferred embodiment with the tip bent above the needle; 
     FIG. 6 is a side sectional view of a tip of a prior art needle; 
     FIG. 7 is a top plan view of the needle tip shown in FIG. 6; and 
     FIG. 8 is a side elevation view of the needle shown in FIGS. 6 and 7 following dulling of the needle tip; 
     FIG. 9 is a graphical representation of a collection rate as a finction of needle tip displacement for a needle such as that shown in FIGS. 5A and 5B; and 
     FIG. 10 is a scatter chart of a collection rate as a function of the bend angle of a needle tip for a needle such as that shown in FIGS.  5 A and  5 B. 
    
    
     DETAILED DESCRIPTION 
     Various embodiments of the present invention, including a preferred embodiment, will be described in detail with reference to the drawings wherein like reference numerals represent like parts and assemblies throughout the several views. Reference to the described embodiments does not limit the scope of the invention, which is limited only by the scope of the appended claims. 
     Throughout the following description, an embodiment of the present invention will be described with reference to collecting a sample of interstitial fluid for glucose testing using a narrow needle that penetrates into, but not through, the dermis. Such sample collection is more fully described in commonly assigned U.S. Pat. Nos. 5,823,973 and 5,820,570, the disclosures for both of which are hereby incorporated by reference as though set forth in full. While such a use is a preferred embodiment, the present invention is applicable to other fluid collection systems as well as testing for other fluid analytes. 
     FIG. 1 illustrates a fluid sampler  410  such as that shown in FIGS. 36-40 of U.S. Pat. No. 5,823,973 (the &#39;973 patent), the disclosure of which is hereby incorporated herein by reference. FIG. 2 illustrates a membrane and needle assembly such as that shown in FIG. 43 of the &#39;973 patent. For ease of illustration, the present invention will be described to a needle alignment such as that shown in the &#39;973 patent with the axis of the needle parallel to the surface of an absorbing membrane. The invention could also be used in other arrangements. For example, the needle axis can be perpendicular to the membrane and fluid can flow through the membrane to an opposite side for colormetric testing. 
     Referring now to FIGS. 1 and 2, the sampler  410  has a hollow handle end  409  with an interior  500  to receive a sample end  411 . The sample end  411  pivots on a pin  502 . The sample end  411  then can pivot between a storage position within the hollow handle end  409  and a deployed position. FIG. 1 shows the sample end  411  pivoted into the deployed position. 
     The sample end  411  is configured to receive samples such as a fluid. An absorbent membrane  504  is carried on the sample end  411 . The sample end  411  also includes a hub or ferrule  506  that terminates at a ring end  508 . In one possible embodiment, the ring end may serve as a pressure ring. A needle  510  is held by the ferrule  506 . Additionally, the sample end  411  defines a hole  604  (FIG.  2 ). An absorbent membrane  504  has a target area T and is arranged so that the target area T overlies the hole  604 . 
     As shown in FIG. 3, the needle  510  includes a hollow, straight tubular body  514 , a first or penetration end  600 , and a discharge end  601  (shown in FIGS.  1  and  2 ). In one embodiment, the needle  510  is a 30 gauge needle, about 0.3 mm in outside diameter, although other needle gauges can be used. In a preferred embodiment, the penetration end  600  protrudes from the ring end  508  of the ferrule by a predetermined distance. The predetermined distance is set so that the first end  600  will penetrate into, but not through, a patient&#39;s dermis when the ring  508  is placed against his or her skin. 
     The discharge end  601  abuts an absorbent membrane  504  mounted on the sample end  411 . In this configuration, the longitudinal axis of the needle  510  is perpendicular to the portion of the membrane  504  that forms the target area T. Additionally, the tubular body  514  has an interior surface  511  (FIG. 5) that defines a fluid pathway  512  extending completely through the needle body  514 . 
     In use, the penetration end  600  of the needle  510  is inserted into the patient&#39;s dermis. Fluid then flows along the fluid pathway  512  and through the absorbent membrane  504  to the target area T. The absorbent membrane  504  filters out undesirable stray blood cells that may be present in the fluid. The fluid at the target area can then be tested for elements such as glucose. 
     One possible way to test the fluid is through the use of infrared light. Alternative embodiments include but are not limited to depositing the fluid on a test strip for colormetric testing or on electrodes for electro-chemical testing. 
     Referring to FIGS. 4 and 5, the needle  510  has a primary beveled face  520  and tip  530  formed at its penetration end  600 . An entrance hole  521  is formed in the beveled face  520  and is in fluid communication with the fluid path  512 . The needle  510  also has a front side  522  and an opposite back side  523 . The tip  530  of the needle  510  is displaced toward the front side  522  of the needle  510 . 
     Referring to FIG. 3, one possible way to form the needle  510  is as follows. The penetration end  600  of the hollow body  514  is ground at an angle to define the beveled face  520  so that it extends through the body  514  and forms the sharp penetration tip  530 . In one possible embodiment, the beveled face is formed at an angle β (about 9°) with respect to a longitudinal axis CL—CL of the needle body  514 . The formation of a beveled face  520  results in formation of the entrance hole  521  on beveled face  520 . The present invention is shown with a needle having a single grind forming the beveled face. The present invention is also applicable to needles with multiple grinds forming the beveled face. 
     After providing a needle body  514  with a flat beveled face  520 , a fulcrum  700  is placed at a bend location, which is a distance X from the tip  530 . In one possible embodiment, the distance X is about 1.2 mm, although other distances can be used. The tip  530  is then urged toward the front side  522  to permanently displace the tip  530  and form a bend angle α. When the tip  530  is displaced, it moves from being aligned with a plane of the back side  523  of the body  514  to a location spaced by a distance Y from the plane of the back side  523 . This method creates an arcuate bend which is approximated in the Figures by the bend angle α. In one possible embodiment, the bend angle α is about 27.1°, although other bend angles are possible. 
     For reasons not fully understood, the use of a displaced tip  530  results in enhanced fluid collection. Possibly, a pocket is formed around the opening  521  to improve fluid flow. Whatever the mechanism, fluid collection is enhanced. Further, the degree of enhancement improves with the amount of deflection Y. The following table illustrates the amount of time required to collect an adequate sample (in the test presumed to be about 0.9 μl of fluid) for an average of needle samples at various tip displacements Y and for a variety of axial locations X (with X and Y as defined with reference to FIG.  3 ). The amount of time greatly decreases with an increase in Y. In fact, displacement of the tip above the front plane of the needle body has resulted in enhanced collection. In the following table, negative values of a and Y reflect a backward bending of the tip behind the rear side of the needle. Zero values reflect an unbent needle. 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE A 
               
             
             
               
                   
               
               
                 Time to Collect Pre-determined Amount of Sample 
               
             
          
           
               
                   
                 Location 
                 Angle 
                   
                 Time to Collect 
               
               
                   
                 X 
                 α 
                 Displacement Y 
                 .9 μl of Sample 
               
               
                   
                 (mm) 
                 (degrees) 
                 (mm) 
                 (seconds) 
               
               
                   
                   
               
             
          
           
               
                   
                 1.07 
                 −6.03 
                 −0.14 
                 26.75 
               
               
                   
                 0 
                 0 
                 0 
                 15.51 
               
               
                   
                 0.88 
                 3.24 
                 0.09 
                 12.75 
               
               
                   
                 1.57 
                 5.71 
                 0.13 
                 10.41 
               
               
                   
                 0.86 
                 11.3 
                 0.15 
                 11.46 
               
               
                   
                 2.03 
                 8.13 
                 0.25 
                 12.74 
               
               
                   
                 1.30 
                 12.8 
                 0.279 
                 9.04 
               
               
                   
                 0.59 
                 28.3 
                 0.281 
                 7.63 
               
               
                   
                 1.68 
                 13.7 
                 0.38 
                 7.96 
               
               
                   
                 0.94 
                 25.9 
                 0.43 
                 6.62 
               
               
                   
                 1.41 
                 21.6 
                 0.51 
                 5.66 
               
               
                   
                   
               
             
          
         
       
     
     FIGS. 5A and 5B illustrate a preferred embodiment where the tip  530 ″ is displaced above the front side  522 ″ of the needle  510 ″. In FIGS. 5A and 5B, elements in common with those of the embodiment of FIGS. 3-5 are similarly numbered (and need not be separately discussed beyond what follows) with the addition of a double apostrophe to distinguish the embodiments. 
     The needle  510 ″ is 0.012 inch (about 0.3048 mm or 30 gauge) outside diameter. 
     The preferred embodiment was derived following experimentation subsequent to that enumerated in the above table. In FIG. 5B, the bend angle θ is the lesser included angle of a straight line A tangent to the bent portion  600 ″ and an extension line B of the straight portion. The distance Y is the distance between the tip  530 ″ and the straight line extension B. The distance X is the distance from the intersection of the tangent line A and straight line extension B to the tip  530 ″. All of the data in the following table illustrate fluid collection rate (measured in micro-liters per second, μl/sec.) as measured using a preferred value of X equal to 0.035 inch (about 0.8890 mm). The negative values for θ and Y represent a downward bend. Positive values represent upward bends as illustrated in FIG. 5B. A zero value represents an unbent needle. 
     
       
         
               
             
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE B 
               
             
             
               
                   
               
               
                 Fluid Collection Rate (Micro-Liters/Second) 
               
             
          
           
               
                 Bend 
                 VALUES of Y 
               
             
          
           
               
                 Angle 
                 −.006 inch 
                 .000 inch 
                 .005 inch 
                 .012 inch 
                 .016 inch 
                 .020 inch 
               
               
                 (θ) in 
                 (≅−.1524 
                 (≅.0000 
                 (≅.1270 
                 (≅.3048 
                 (≅.4064 
                 (≅.5080 
               
               
                 degrees 
                 mm) 
                 mm) 
                 mm) 
                 mm) 
                 mm) 
                 mm) 
               
               
                   
               
             
          
           
               
                 −8.1 
                 0.06 
                   
                   
                   
                   
                   
               
               
                 0.0 
                   
                 0.10 
                   
                   
                   
               
               
                 4.6 
                   
                   
                 0.13 
                   
                   
               
               
                 6.5 
                   
                   
                 0.13 
                   
                   
               
               
                 7.1 
                   
                   
                   
                 0.12 
                   
               
               
                 7.6 
                   
                   
                 0.10 
                   
                   
               
               
                 10.0 
                   
                   
                 0.14 
                   
                   
               
               
                 12.2 
                   
                   
                   
                 0.15 
                   
               
               
                 12.2 
                   
                   
                   
                 0.13 
                   
               
               
                 12.8 
                   
                   
                   
                   
                 0.16 
               
               
                 14.9 
                   
                   
                   
                 0.13 
                   
               
               
                 16.8 
                   
                   
                   
                 0.13 
                   
               
               
                 20.0 
                   
                   
                   
                   
                   
                 0.19 
               
               
                 21.6 
                   
                   
                   
                   
                   
                 0.17 
               
               
                 21.8 
                   
                   
                   
                 0.16 
                   
               
               
                 24.7 
                   
                   
                   
                   
                 0.19 
               
               
                 25.6 
                   
                   
                   
                 0.18 
                   
               
               
                 26.6 
                   
                   
                   
                 0.15 
                   
               
               
                 31.2 
                   
                   
                   
                   
                   
                 0.20 
               
               
                 46.4 
                   
                   
                   
                   
                   
                 0.20 
               
               
                   
               
             
          
         
       
     
     Using the above data, FIG. 9 is a graphical representation of the collection rate (μl/sec.) as a function of the Y displacement (where Y is the average Y values for various angles from the data in FIG. θ). FIG. 10 is a scatter chart of the data plotted as collection rate (μl/sec.) as a function of the bend angle θ. 
     The above data show for a small gauge needle, collection rate improves with increases in both the bend angle θ and the displacement Y. In fact, displacements greater than the needle&#39;s outside diameter of 0.012 inch (representing a bending of the tip  530 ″ above the front side  522 ″ of the needle  510 ″) shows improved collection rates. 
     Since pain avoidance is a desirable feature, patients selected to collect the above data were asked to compare pain sensation using the above-configured needles. While pain is subjective, it was surprising to note the patient population did not record appreciable increase in pain until the bend angle θ exceeded 30°-40°. The data suggest optimum design of a low pain needle for maximizing fluid collection rates is to provide a bend angle θ of about 30° and preferably between 20° and 40° with the tip  530 ″ of the needle bent above the plane of the needle  510 ″. 
     In certain applications (for example, collecting interstitial fluid for testing), it is desirable for the fluid to have a low blood content so as to be substantially blood-free. By substantially blood free, it is meant a sample with a hemocrit content of less than 10%. Using the bent needle  510 ″ as described, the frequency of occurrence of blood in a sample increases compared to a straight needle, but the samples continue to be substantially blood free. The present needle  510 ″ can also be used to collect higher blood content samples. In both, the design as described increases flow rate while retaining a low pain quality. 
     In addition to the bend angle described above, the needle  510  is dulled at the penetration end. The dulled edges at the penetration end have benefits separate from the displaced tip described above. Specifically, the dulled edges are found to reduce the amount of unwanted blood in a collected sample of interstitial fluid. 
     FIGS. 6-8, illustrate a needle having a straight tip before and after its edges are dulled. Although the dulled edges are illustrated on a needle having a straight tip, they also could be used in conjunction with a displaced tip as described above. Elements and structures that are in common with the embodiments described above are marked with the same reference numerals with the addition of an apostrophe. 
     Referring now to FIGS. 6 and 7, the beveled face  520 ′ is initially formed by grinding the needle  514 ′ at the penetration end  600 ′ as discussed above to form opening  521 ′ (shown in FIG.  7 ). This grinding forms an outer peripheral edge  630 ′, which is defined by the intersection of the beveled face  520 ′ and the outer surface of the cylindrical body  514 ′. Additionally, an inner peripheral edge  632 ′ is defined by the intersection of the beveled face  520 ′ and the interior surface  511 ′ of the needle body  514 ′. Upon grinding the needle to form the beveled face  520 ′, the inner and outer peripheral edges  630 ′ and  632 ′ and tip  530 ′ are initially sharp (i.e., are formed at substantially non-rounded intersections). 
     After the beveled face  520 ′ is formed, the inner and outer edges  630 ′ and  632 ′ and tip  530 ′ are dulled so that they become burnished or radiused. The dulled edges are formed in a burnishing operation by tumbling the needle  510 ′ in a tumbler with a polishing medium. In one possible embodiment, the polishing medium is a fine media such as 1 mm ceramic spheres and a soap solution. About 5,000 needles are tumbled in a single batch in the polishing medium for about 20 minutes. Other possible tumbling methods use a different polishing medium, different batch sizes, or different lengths of time. 
     Referring to FIG. 8, this process dulls the inner and outer edges  630 ′ and  632 ′ and tip  530 ′. In one possible embodiment, the edges  630 ′ and  632 ′ and tip  530 ′ are dulled to a radius of about 0.002 inch or about 0.05 mm. Although a burnishing process is described herein, manufacturing processes other than tumbling may be used to form the dulled edges. 
     From the foregoing detailed description, the present invention has been described in a preferred embodiment. Modifications and equivalents of such disclosure are intended to be included in the appended claims. For example, the benefits of the displaced tip can be attained without the dulled edges of the needle. Similarly, the benefits of the dulled edges can be attained without the displaced tip of the needle. Additionally, all needles have been shown with a single bevel. Nevertheless, the present invention is applicable to a needle with multiple bevels.