Blood microsampling site preparation

Abstract: A method for collecting blood while preserving the integrity of the blood sample includes the steps of applying a protective layer to the skin, lancing the skin through the protective layer, allowing blood from the subject to accumulate on the protective layer, and collecting a sample of the blood accumulated on the protective layer. The protective layer may be formed in situ or applied as a tape. In either case, the surface of the protective layer should be hydrophobic.

Description: BACKGROUND OF THE INVENTION The field of the invention relates to the sampling of blood through the techniques of lancing the skin and collecting blood through the use of a capillary tube or other collection device. Blood samples are generally obtained through the use of syringes when relatively large samples are required. Smaller samples may be obtained by simply lancing a finger or other part of a subject's body, waiting for a blood drop to form, and moving the end of a capillary tube into contact with the drop. Blood is collected by means of capillary action. U.S. Patent No. 4,589,421 discloses a method for performing the latter technique. Blood samples obtained from lanced skin sites are likely to be contaminated with skin oils and bacteria even if the sites are first washed. There may also be triggering of platelets in the blood upon skin contact. In addition, the blood often tends to spread out over the skin, making it more difficult to obtain a sample and increasing the likelihood of the blood contacting the phlebotomist. SUMMARY OF THE INVENTION It is an object of the invention to provide the use of a compound for preparing a formulation which is suitable for a method for sampling blood from a subject which avoids a number of problems ordinarily encountered when obtaining blood from lanced skin sites. It is another object of the invention to provide the use of a compound for preparing a formulation which is suitable for a method for sampling blood which provides a better quality blood sample than when using conventional techniques. A still further object of the invention is to facilitate the sampling of blood from lanced skin sites. In accordance with these and other objects of the invention it is provided the use of a compound having the general formula wherein EWG is an electron withdrawing group, R 1 is an alkyl or hydrogen, and R 2 is an alkyl or alkenyl for preparing a liquid or gelatinous formulation being suitable for in situ polymerization to form a hydrophobic protective layer on skin, said protective layer being suitable for allowing lancing a portion of the skin through the protective layer; allowing blood from the lanced portion of the skin to accumulate on a surface of said protective layer; and collecting a sample of said blood accumulated on said protective layer. The blood sample may be taken by means of a capillary tube. By using a protective film which is non-wetting, the blood is easier to pick up than if it is allowed to spread over the skin. The integrity of the blood sample is maintained by using this procedure as it never contacts the subject's skin. DETAILED DESCRIPTION OF THE INVENTION The invention provides the use of particular acrylate monomers or oligomers for preparing a liquid or gelatinous formulation being suitable for in situ polymerization to form a hydrophobic protective layer on skin for preserving the integrity of a blood sample obtained from a subject through an opening in the skin. A thin, protective film is first applied to the subject's skin on the area which the phlebotomist intends to lance. As will be described hereafter, the film may be applied as a liquid or gelatinous formulation, wherein a thin film will remain upon the skin on or shortly after application. The film is hydrophobic. Next, the skin protected by the film is lanced with a lancet or any other suitable medical instrument designed for cutting or piercing the skin. Only a small incision is desirable or necessary. Once the skin is pierced, blood flows through the incision and collects upon the protective film. The film should be applied over a sufficient area that the blood does not contact the skin. The skin is preferably lanced near the center of the area covered by the film to insure the blood contacts nothing but the film. As the blood collects upon the film, it will tend to form as a drop due to cohesion. The film, being substantially non-wetting, discourages the spreading of the drop about the lanced site. The film should also be non-thrombogenic. Once a sufficient amount of blood has accumulated about the lanced site, it may be collected by the phlebotomist. One common method of collecting blood is to contact the blood with the end of a capillary tube and allow the tube to fill by capillary action. Another method is to allow the blood to drip into a container which can be used for storage and/or analysis. By employing a hydrophobic film in accordance with the invention, the blood is easier to collect as it does not tend to spread upon the subject's skin. More blood is available for collection by using the above techniques as it does not adhere to the film as it does to skin. Larger samples are accordingly available for the laboratory. The method wherein the film according to the invention is used is also more aseptic than the conventional procedure, the film protecting both the patient and the blood sample. The protective film is formed in situ. This is accomplished by smearing a liquid or gelatinous formulation containing acrylate monomers or oligomers over the area of interest into a thin film. Exposure to air triggers a polymerization reaction of the residual acrylates forming a thin, solid hydrophobic film. Once the skin is pierced through the film and blood collected, the film may be peeled away or removed with a solvent. A monomer having the general formula shown below is used for in situ polymerization on a subject's skin: where EWG is an electron withdrawing group such as CN or NO 2 , R 1 is an alkyl or hydrogen, and R 2 is an alkyl or alkenyl (C 1 -C 18 ) or other homolog. The hydrophobic nature and physio-mechanical properties of the polymers used are controlled by variations in R 1 and R 2 . For example, hydrophobicity will increase as the chain lengths of these groups increase. The formulation applied to the skin for in situ polymerization is applied in the absence of a solvent. A less preferred method of providing in situ polymerization is through the use of activated acrylates wherein the activation mechanism is infrared light. In addition to providing a hydrophobic surface which facilitates the collection of blood while maintaining the integrity of the blood sample, the protective film may be formulated to provide other properties as well. The use of alcohol as a solvent provides a disinfectant in the area which is to be lanced. An anticoagulant such as Heparin and an anesthetic such as Lidocaine may also be incorporated within the film material. If the puncture site is pre-warmed, blood flow will be increased, thereby facilitating the collection procedure. Such warming can be accomplished by providing in situ exothermic polymerization, as described above. Although illustrative embodiments of the present invention have been described herein, it is to be understood that the invention is not limited to those precise embodiments.

Claims: Claims for the following Contracting States : AT, BE, CH, LI, DE, DK, FR, GB, GR, IT, LU, NL, SE Use of a compound having the general formula wherein EWG is an electron withdrawing group, R 1 is an alkyl or hydrogen, and R 2 is an alkyl or alkenyl for preparing a liquid or gelatinous formulation being suitable for in situ polymerization to form a hydrophobic protective layer on skin, said protective layer being suitable for allowing lancing a portion of the skin through the protective layer; allowing blood from the lanced portion of the skin to accumulate on a surface of said protective layer; and collecting a sample of said blood accumulated on said protective layer. The use as defined in claim 1 wherein said protective layer includes an anticoagulant. The use as defined in claim 1 wherein the electron withdrawing group is CN or NO 2 . Claims for the following Contracting State : ES A method of preparing a liquid or gelatinous formulation being suitable for in situ polymerization to form a hydrophobic protective layer on skin, said protective layer being suitable for allowing lancing a portion of the skin through the protective layer; allowing blood from the lanced portion of the skin to accumulate on a surface of said protective layer; and collecting a sample of said blood accumulated on said protective layer, which method comprises formulating a compound having the general formula: wherein EWG is an electron withdrawing group, R 1 is an alkyl or hydrogen, and R 2 is an alkyl or alkenyl. The method as defined in claim 1 wherein said formulation includes an anticoagulant. The method as defined in claim 1 wherein the electron withdrawing group is CN or NO 2 .

Inventors: HAYNES JOHN L, TITUS GEORGE R, HAYNES, JOHN L., TITUS, GEORGE R.
Applicants: BECTON DICKINSON CO, BECTON DICKINSON AND COMPANY
Application year: 1990
Main classification: A61B5
IPC codes: A61F13, A61B5