1. Field of the Invention
The present invention relates to a method and tool for collecting blood plasma, and particularly to a technology for effectively collecting only blood plasma by separating blood plasma and blood cells (red blood cells, white blood cells, blood platelets) in blood from each other in a short time before a blood test.
2. Description of the Related Art
When a blood test is conducted, blood of several mL is collected depending on measurement items by a vacuum blood collecting tube and the vacuum blood collecting tube is set up on various automatic analyzers. The automatic analyzers are large and some hospitals may sometimes ask a test center to inspect blood because of no possession of test equipment. Therefore, it is the present situation that it takes a time to obtain the inspection result. When an emergency clinic test is conducted, it is required to go to facilities having test equipment, so that the test itself is a physical load to old people and the sick. Further, if the environment allowing a blood test to be conducted more readily and more frequently is prepared, protective measures against illness may be enhanced and the quality of life may be improved.
Now, blood used for a blood test may be frequently analyzed optically, and it is known that a solid body in blood, for example, hemoglobin in red blood cells, especially its own color prevents colorimetric measurement. Therefore, in order to provide an accurate test result, as pretreatment for a blood test, it is necessary to prepare a specimen only composed of blood plasma (including serum) obtained by separating blood cells from blood. For this purpose, in order to readily collect only blood plasma by separating to remove blood cells from blood at the site where a blood test is conducted, not limited to a big hospital or a test center equipped with a large blood plasma collection system, the blood plasma collection system has to be made smaller to be a simple test instrument and a blood plasma collection method is required to be made simpler. Further, to mitigate a physical and psychological impact of a patient undergoing a blood test, it is necessary to test by a small amount of blood collected.
In such circumstances, the following items are required for a blood plasma collection method and tool.
(1) Blood plasma collection has to be simple using a small tool and an operation for collection of a small amount of blood. For example, in order to readily implement collection of blood and to allow test to be conducted by anyone anywhere, an amount of blood collected has to be reduced to the degree of several dozens μL at the most, which may be collected by a lancet.(2) A time necessary to collect blood plasma, that is, a separation time for separating blood plasma and blood cells from each other has to be shortened as much as possible, because fresh blood changes as time passes and becomes unusable for test.(3) Medicines such as a separation agent do not have to be used, because they may degrade test accuracy.
For these items, there are the following systems as a conventional blood plasma collection system or tool.
Japanese Patent Application Laid-Open No. 2003-83958 discloses a method for separating blood plasma and blood cells from each other by the centrifugal separation method, and the method has a problem of a long separation time, as well as an additional operation for putting blood plasma into a blood test device after separating out blood cells. Japanese Patent Application Laid-Open No. 2006-52950 discloses improvement in size of a device which, based on the centrifugal separation method, was made large, and proposes a method that blood is introduced into a microchip and the microchip is entirely run by a centrifugal separator, but miniaturization of the device is restricted by necessity of a high speed rotating part.
Japanese Patent Application Laid-Open No. 2003-270239 discloses a method for separating blood plasma and blood cells from each other by the membrane separation method, and the method can collect a very small amount of blood to separate, but to implement this method, dilution of the collected blood or extraction of blood plasma to be tested from a small container is required, resulting in complicated operation. Further, because a membrane, used for the membrane separation method, itself has water holding capacity, a part of a specimen may be readily damaged, moreover because it is necessary to push out blood into a filter by pressurization, unfortunately the filter may clog or hemolysis may occur.
Japanese Patent Application Laid-Open No. 2000-171461 discloses a method except the centrifugal separation method and the membrane separation method, in which, by alternately laying cation exchange material and anion exchange material one on the other on a surface of a substrate for introducing blood, the surface of the substrate is made to be charged with cations, and then red blood cells (a sort of blood cells) charged with anions are captured electrically on the surface of the substrate. However, this method has a problem of troublesome coating, as well as quite conceivable, electrostatic attachment of components in blood plasma.
Further, Japanese Patent Application Laid-Open No. 2005-292092 also discloses a method except the centrifugal separation method and the membrane separation method, in which solid components and liquid components in blood are separated from each other by adding flocculant (separation assistant) to a small amount of blood to generate aggregate and precipitating out the aggregate through a channel structure. However, this method has a problem that the channel has a complex shape and it takes a time to effect agglutination, moreover the flocculent may have a bad influence on a blood test.
Further, conventionally, blood plasma having blood cells separated out is generally inspected at another place, which is a time loss, and also a specimen loss. Therefore, desired is a method by which separation of blood cells and a blood test can be conducted concurrently at the same place.