Abstract:
A method of dispensing gel for separation of the serum and coagulum portions of a blood sample in a blood collection tube is disclosed. The present invention of dispensing the gel preferably comprises utilizing a gel dispensing apparatus with a nozzle head having a plurality of openings. The gel dispensing apparatus dispenses either a continuous band of gel around the central portion of the collection tube or a plurality of discrete stripes that forms a circumferential pattern thereto. Once the gel is dispensed, the tube is ready for accepting a blood sample for eventual separation in a centrifuge where the dispensed gel will form a barrier that exhibits strong adhesive properties after separation of the blood sample has occurred.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to the method and apparatus for separating blood components in a blood collection device. Specifically, the invention relates to a method for the separation of the light serum portion of blood from the heavy cellular portion of blood, the blood collection device used to collect and separate the blood, and the method of manufacturing the blood collection device. More particularly, the invention relates to a method of dispensing separator gel in a blood collection tube for improving gel barrier stability and adhesion of the gel to the tube wall during the separation process. 
     PRIOR ART 
     Blood collection devices for separating the lighter serum portion of a blood sample from the heavier cellular portion thereof are well known. These devices usually comprise a collection tube containing a thixotropic gel and a contact activated clotting agent. The gel has a specific gravity intermediate the specific gravity of the serum and the cellular phases of the blood sample. 
     After a sample of blood has been deposited into the collection tube, the contact-activated clotting agents begin to clot the blood sample by activating clotting factors within the blood. The agent facilitates the clotting process until the blood is completely coagulated. It is essential that the agent coagulate substantially all of the blood sample in order for the subsequent serum separation process to be complete. Once the blood has coagulated, the collection tube is placed in a centrifuge to separate the lighter serum from the heavier coagulum portion. Coagulum is defined as the cellular portion and fibrin clot of the blood as opposed to the lighter serum portion of the blood. During centrifugation, the gel on the bottom of the collection tube is displaced upwardly through the blood sample until it reaches its equilibrium position at the interface between the serum and the coagulum. In this position, the gel forms a barrier between the serum and the coagulum which permits the lighter serum to be either decanted directly from the collection tube, or sampled using automated blood analyzing equipment, without interference from the coagulum. 
     It has long been known in the art that human blood can be readily centrifuged to effect a separation of the blood into its lighter serum and heavier coagulum portions. The specific gravity of the serum portion of human blood is between approximately 1.026 and 1.031, while the specific gravity of the coagulum portion of human blood is between approximately 1.092 and 1.095. The specific gravity of the gel is therefore chosen to be approximately between 1.032 and 1.091, so that once a blood sample is centrifuged, the gel will form an effective barrier between the serum and the coagulum. A preferred gel to be used with the method of the present invention is a thixotropic composition described in U.S. Pat. No. 4,140,631 to Okuda et al, entitled “Sealant for Separation of Serum or Plasma, and It&#39;s Use”, the entire disclosure of which is hereby incorporated by reference. As described in Okuda et al., the preferred thixotropic gel is a polymer essentially consisting of at least one compound from the group of alkyl acrylates and alkyl methacrylates, which has a specific gravity of 1.03 to 1.08 and a viscosity of about 5,000 to 1,000,000 cps at a shear rate of 1 second− 1  when measured at 25° C. However, any suitable gel-like composition which can be used as a barrier between blood portions separated in a centrifuge is felt to fall within the spirit and scope of the present invention. 
     This type of gel is adapted to migrate or flow from the bottom of the tube under the influence of centrifugation to the interface position between the serum and the coagulum portions of the blood and adhere to the inside surface of the collection tube wall to form a barrier between the blood portions to maintain a separation therebetween. However, this migration causes an attendant loss of gel along the tube wall, thereby requiring initial placements of larger amounts of gel in the tube in order to insure the formation of a strong enough mechanical barrier to properly separate the two portions of blood during centrifugation. 
     Weak adhesion of the gel to the collection tube&#39;s inner surface during centrifugation of the blood sample is a problem with prior art blood collection devices. Such weak adhesion of the gel is due to the blood sample wetting the inner surface of the blood collection device prior to the migration of the gel. This wetted inner surface inhibits the natural adhesive properties of the gel, thereby preventing the gel from forming a strong adhesive bond thereto. U.S. Pat. No. 4,257,886 seeks to overcome this deficiency by disclosing a blood separation assembly that coats the bottom portion of the collection tube with a hydrophobic material that resists wetting of the collection tube&#39;s inner surface and allows the gel to form a strong adhesive bond to the inner surface during centrifugation. 
     Another method of addressing the gel migration problem with its attendant loss of adhesion is found in U.S. Pat. No. 4,417,981 (hereinafter the &#39;981 patent) which attempts to overcome the problems associated with gel migration by dispensing the gel in a separator assembly located in the central portion of the collection tube near the eventual formation of the gel barrier. The pre-placement and dispensation of the gel in a separator assembly permits the gel to quickly adhere to the tube wall during centrifugation without migration and attendant loss of gel. However, the above method of dispensing gel using a device incurs further expense in manufacturing an additional element to attain proper separation of the blood sample. 
     Referring to FIGS. 1-4, the prior art method of dispensing separator gel  3  and separating a blood sample into two portions is shown. The method involves utilizing a commonly known gel dispensing apparatus (not shown) to dispense a predetermined amount of gel  3  into the bottom  5  of a collection tube  2 . Contact-activated clotting powder or particles  6  are then deposited inside the collection tube  2  for eventual activation of clotting factors within blood  7  after blood  7  is added to the tube  2 . 
     As shown in FIG. 2, a predetermined amount  4  of blood  7  is added to the collection tube  2  and the contact clot-activating material  6  within tube  2  begins to coagulate the blood  7  before the tube  2  is placed in a centrifuge (not shown) for centrifugation of the blood  7 . The contact clot-activating material  6  promotes clot formation and includes but is not limited to glass and silica. Referring now to FIG. 3, during centrifugation of the blood  7  in the collection tube  2 , the gel  3  becomes less viscous and begins to migrate upward along the tube&#39;s  2  inner surface  8  until it reaches an interface point  9  where the lighter serum portion  10  of the blood  7  begins to separate from the heavier coagulum portion  11 . The interface point  9  is a result of the two portions of blood, serum  10  and coagulum  11 , being physically separated due to the effect of their different specific gravities during centrifugation. As shown in FIG. 4, the separation gel  3 , having a specific gravity intermediate that of the serum  10  and coagulum  11 , has migrated to the interface point  9  between the two blood portions. At the interface point  9 , the gel  3  forms a mechanical barrier  12  inside the collection tube  2  that physically separates the two blood portions and prevents the serum  10  from being contaminated by coagulum  11 . 
     As of yet, nothing in the prior art has addressed the problem of developing an efficient means of dispensing gel that does not suffer from either attendant loss of gel caused by migration or weak adhesive properties when the gel barrier  12  is formed. 
     Therefore, there exists a need in the blood collection art for an improved means of dispensing gel into a collection tube in an inexpensive and efficient manner which promotes both quick formation of the barrier separating the two blood portions and strong adhesion of the barrier to the collection tube&#39;s inner surface once the gel barrier is formed. 
     SUMMARY OF THE INVENTION 
     In brief summary, the present invention relates to a means of dispensing gel for separation of the lighter serum portion and the heavier coagulum portion of a blood sample in a blood collection tube. The preferred method of dispensing the gel comprises utilizing a gel dispensing apparatus with a nozzle head or like portion having a plurality of openings. The gel dispensing apparatus dispenses either a continuous band of gel around the central portion of the collection tube or a plurality of discrete stripes that flow to form a continuous band pattern around the central portion of the collection tube. Once the gel is so dispensed about the central portion of the collection tube, the tube is ready for accepting a blood sample for eventual separation in a centrifuge where the dispensed gel will form a barrier between the serum portion and the coagulum portion of the blood sample while exhibiting strong adhesive properties, i.e., few to no points of fluid communication between blood portions. 
     The present invention includes a method of dispensing gel in a tube is claimed having opposed open and closed ends, a central body portion between the opposed open and closed ends, and an interior surface formed by the central body portion and the closed end, comprising the steps of: providing the tube providing a gel dispensing apparatus for dispensing a gel into the tube, placing a portion of the apparatus inside the tube, dispensing the gel from the portion of the apparatus onto an interior wall surface formed by the central body portion, and terminating the dispensation of the gel. 
     The present invention further includes a blood collection device for use in separating blood into different portions comprising a tube having a central body portion, opposed closed and open ends, and an interior surface with gel dispensed on an interior wall surface thereof. Optionally, contact clot activating particles may be placed within the device. 
     The present invention still further includes a method of separating blood into different portions using the aforementioned blood collection device optionally containing contact clot-activating particles comprising the steps of: placing a blood sample inside the blood collection device, centrifuging the device containing the blood sample wherein centrifuging the device and the blood sample permits the gel to flow inwardly from the interior wall surface to form a barrier between the different portions of the blood sample after centrifugation is completed. 
     Accordingly, a principal object of the present invention is to provide an efficient and inexpensive method for dispensing gel in a collection tube for use in separating a blood sample into portions. 
     Another important object of the present invention is to provide an improved method of dispensing gel that requires minimal or no migration of the gel along the tube wall to form a barrier between portions of blood being separated during centrifugation. 
     A further object of the present invention is to provide a method of dispensing gel that forms continuous and a stable barrier in a short period of time and exhibits strong adhesive properties, i.e., few to no points of fluid communication between the blood portions. 
     Another important object of the present invention is to provide a means of dispensing gel in discrete stripes or a contiguous band around the interior wall surface of a collection tube. 
     A further object of the present invention is to provide a blood collection device that has gel dispensed on the interior wall portion of a tube. 
     Another principal object of the present invention is to provide a method of using a tube with gel dispensed on the inner surface thereof for separation of blood into separate portions. 
    
    
     Additional objects, advantages and novel features of the invention will become apparent to those skilled in the art upon examination of the following more detailed description and drawings in which like elements of the invention are similarly numbered throughout. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows the prior art method of dispensing gel at the bottom of a blood collection tube; 
     FIG. 2 shows the prior art blood collection tube of FIG. 1 after a blood sample has been added thereto; 
     FIG. 3 shows the prior art migration of gel toward the serum/coagulum interface during centrifugation of the blood sample; 
     FIG. 4 shows the prior art blood collection tube after centrifugation of the blood sample and the formation of the gel barrier at the interface between the two portions of the blood; 
     FIG. 5 shows the preferred present method of dispensing gel on the interior wall portion of a collection tube using a nozzle head for dispensing gel in a contiguous band around the interior wall portion of the collection tube; 
     FIG. 6 shows a top section view of the blood collection tube of FIG. 5 showing the gel on the inner surface of the tube with an opening therethrough; and 
     FIG. 7 shows the blood collection tube of the present invention demonstrating the method of determining the lower and upper limits for dispensing gel. 
     FIG. 8 is a perspective view of the gel dispensing apparatus showing the alternative embodiment of a continuous opening at the nozzle head. 
    
    
     DETAILED DESCRIPTION 
     In the preferred method of dispensing gel within a blood collection tube as illustrated in FIG. 5, a blood collection device  20 , preferably a conventional collection tube  21  having an opposed open end  23  and closed end  34  is made of a material which is non-interactive with the blood  35 , such as but not limited to plastic, glass, plastic-lined glass or glass-lined plastic. The collection tube  21  has separator gel  22  which is a thixotropic substance dispensed into the central portion of tube  21  between opposed open end  23  and closed end  34  prior to adding a blood sample  35 . Gel  22  is placed within the tube  21  by using a positive displacement metering apparatus  24  that uses a nozzle head  25  for dispensing a gel or the like. The nozzle head  25  includes one or more openings but preferably a plurality of openings  26  located at its free distal end  31 . If one opening is provided at the free distal end  31 , the opening is preferably a continuous opening around the periphery of an exterior surface  35  of nozzle head  25  as illustrated in FIG.  8 . Although one or more openings  26  can be utilized for the present invention, the preferred embodiment having a plurality of openings  26  will be exemplified throughout the remainder of this description for purposes of simplicity only. The plurality of openings  26  dispense the gel  22  onto the inner surface  29  of the tube  21  in discrete stripes  30  that flow to form a circumferential band pattern around tube  21 . Preferably, the gel  22  is dispensed in discrete stripes  30 , although any suitable configuration that ultimately flows to form one or more continuous bands  30  around the inner surface  29  of the collection tube  21  is felt to fall within the spirit and scope of the present invention. 
     Prior to dispensing gel  22 , the nozzle head  25  is placed inside the collection tube  21  such that openings  26  are positioned at a predetermined lower point  27  to begin dispensing gel  22  along the inner wall surface  29  of tube  21 . As gel  22  is dispensed through openings  26 , the tube  21  is slowly drawn downward so as to move closed end  34  away from the nozzle head  25  until the openings  26  reach a predetermined upper limit  28  near open end  23 . As the dispensing procedure is about to terminate, the nozzle head  25  is slightly ahead of the gel  22  flow, thereby forming a discontinuous circumferential pattern  32  at the predetermined upper limit  28 . In the preferred method of dispensation with a plurality of openings  26 , the discontinuous circumferential pattern  32  formed at the end of dispensation is a crown shape design, but any suitable pattern  32  may be made. Once the dispensation of the gel  22  is terminated, the gel  22  flows and adheres to the inner surface  29  forming a concentric band  30  around the central portion of tube  21  between the predetermined upper and lower limits,  28  and  27  respectively. As better seen in FIG. 6, the gel  22 , after flow thereof has ceased, forms a concentric band  30  with the discontinuous pattern  32  at the top of band  30  and an opening  33  through which the blood sample  35  may initially pass before centrifugation and formation of the gel barrier. After the gel  22  has set or flow has ceased, the collection device  20  is ready for the blood sample  35  to be added for centrifugation and separation as described above. 
     The location of the upper and lower limits,  28  and  27  respectively, in dispensing gel  22  to form a concentric band on the inner surface  29  of the collection tube  21  depends on the size of the tube  21  being utilized and the volume of the blood sample  35  to be added to the tube  21 . Referring to FIG. 7, a general formula for determining the upper and lower limits,  28  and  27  respectively, for gel  22  dispensation will be discussed. X is a variable that represents the volume of the blood sample  35  added to the collection tube  21  prior to centrifugation. In determining the lower and upper limits for gel placement,  27  and  28  respectively, variable X is multiplied by predetermined constants, C LL  for the lower limit  27  and C UL  for the upper limit  28 . These constants are established by one skilled in the art based on the for a particular size of the tube  20  and the particular gel configuration desired. The formulas used are shown below: 
     
       
         lower limit  27 = X ·C LL   
       
     
     
       
         upper limit  28 = X ·C UL   
       
     
     For example if C LL  and C UL  are established as being 0.7 and 0.31 respectively for a particular tube to achieve a particular desired configuration, the lower and upper limits,  27  and  28 , respectively, may be easily determined by knowing the volume of the drawn blood sample  35  added to the collection tube  20 . To illustrate, if a blood sample  35  having a volume of 100 mm is added to the collection tube  21 , the lower limit  27  for dispensing gel  22  would be 70 mm and the upper limit  28  would be  31  mm as set forth below. 
     
       
         lower limit  27 =100 mm×0.7=70 mm 
       
     
     
       
         upper limit  28 =100 mm×0.31=31 mm 
       
     
     Thus, the gel  22  would be dispensed between a range of 31 mm to 70 mm from the open end  23  to form a band  30 . It should be noted that the formula would be varied accordingly if more than one band  30  would be desired for further separation techniques known in the art. 
     The above example is used for the purpose of illustrating the upper and lower limits,  28  and  27  respectively, for dispensing gel  22  in a collection tube  21  made according to the preferred embodiment of the present invention. The above formula insures that a firm mechanical gel barrier is formed after centrifugation regardless of the type of centrifuge used to separate the blood sample  35 . 
     The preferred method of dispensing gel  22  as described above has the advantage of limited migration of the gel  22  during centrifugation while promoting a stronger mechanical barrier after centrifugation. Moreover, dispensing gel  22  on the interior wall portion between upper and lower limits,  28  and  27  respectively, of collection tube  21  has the further advantage of requiring less gel  22  than required in prior art methods in which gel  22  migration was utilized. For example, prior art methods for dispensing gel  22  dispense approximately 2.2 grams of gel  22  to form a sufficient barrier after centrifugation of the blood sample  35  while the present invention requires approximately 1.4 grams of gel  22  to form the same strong barrier. Thus the present invention requires approximately 36% less gel  22  which creates a significant cost savings. 
     Finally, the method of separating a blood sample  35  into different portions using the blood collection device  20  of the present invention will be discussed. The method of separating a blood sample  35  using the blood collection device  20  having contact clot-activating particles  6  previously deposited inside device  20  comprises the first step of providing a blood sample  35  inside the device  20 . After the blood sample  35  is deposited, the sample  35  is then centrifuged, wherein centrifuging the blood sample  35  permits the gel  22  to flow inwardly as the blood sample  35  travels through the opening  33  until a barrier is formed between the different phases of the blood sample  35  once centrifugation is complete. 
     The blood collection device  20  of the present invention may likewise optionally contain contact clot-activating particles such as but not limited to carbon, silica, fumed silica, glass and the like. Likewise, the entire interior surface or a portion of the interior surface of the blood collection tube  21  of the present invention may optionally be sprayed with a water and/or silica mixture to prevent blood from sticking to the sides of the tube. This spray is preferably applied before dispensing of the gel  22  as described above. 
     Optionally, the interior of the blood collection device  20  of the present invention may be sprayed with an ethylene copolymer such as but not limited to polyethylene oxide and/or polydimethyl siloxane to promote gel  22  binding to the wall. 
     Although particular embodiments of the invention have been shown, it is not intended that the invention be limited thereby, instead the scope of the present invention is intended to be limited by the appended claims.