A blood test kit for analyzing a concentration of a target component in a blood sample of 100 μL or less, by using a first normal component homeostatically present in blood, which is sodium ions and a second normal component homeostatically present in blood, the kit comprising: a diluent solution for diluting the blood sample, which is a buffer solution comprising an amino alcohol compound, which is 2-amino-2-methyl-1-propanol,, and contains a buffering agent, which is 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid also called HEPES, wherein a volume of the diluent solution is 10 times or less with respect to a volume of the blood sample, wherein the diluent solution does not contain sodium ions and chloride ions; and the following members: a first storing instrument in which the diluent solution is stored, a separating instrument for separating and recovering blood plasma from the blood sample diluted with the diluent solution, a holding instrument for holding the separating instrument, a second storing instrument for storing the recovered blood plasma, and a sealing instrument for keeping the stored blood plasma in the second storing instrument, wherein the material of the members is plastic, glass, or rubber, wherein the members are washed with pure water having an electric conductivity of 1 μS/cm or less so that an amount of the first normal component which is derived from the member and is contained in the diluent solution is 0.5% by mass or less with respect to the amount of the diluent solution, when the diluent solution is passed through the members according to regular use thereof, wherein the amount of the first normal component, which is derived from the member and is contained in the diluent solution is measured by the enzyme activity method utilizing that β-galactosidase is activated by sodium, wherein the second component which is homeostatically present in blood is total protein or albumins, and wherein the second normal component which is homeostatically present in blood is capable of verifying the analysis of a concentration of a target component of the blood sample. a diluent solution for diluting the blood sample, which is a buffer solution comprising an amino alcohol compound, which is 2-amino-2-methyl-1-propanol,, and contains a buffering agent, which is 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid also called HEPES, wherein a volume of the diluent solution is 10 times or less with respect to a volume of the blood sample, wherein the diluent solution does not contain sodium ions and chloride ions; and the following members: a first storing instrument in which the diluent solution is stored, a separating instrument for separating and recovering blood plasma from the blood sample diluted with the diluent solution, a holding instrument for holding the separating instrument, a second storing instrument for storing the recovered blood plasma, and a sealing instrument for keeping the stored blood plasma in the second storing instrument, wherein the material of the members is plastic, glass, or rubber, wherein the members are washed with pure water having an electric conductivity of 1 μS/cm or less so that an amount of the first normal component which is derived from the member and is contained in the diluent solution is 0.5% by mass or less with respect to the amount of the diluent solution, when the diluent solution is passed through the members according to regular use thereof, wherein the amount of the first normal component, which is derived from the member and is contained in the diluent solution is measured by the enzyme activity method utilizing that β-galactosidase is activated by sodium, wherein the second component which is homeostatically present in blood is total protein or albumins, and wherein the second normal component which is homeostatically present in blood is capable of verifying the analysis of a concentration of a target component of the blood sample.