A blood testing unit comprises a closed vessel having a blood introducing section formed at a certain area of the closed vessel. A blood constituent separating section is located within the closed vessel to separate plasma and/or serum from the blood sample introduced through the blood introducing section into the closed vessel. A reagent layer is located within the closed vessel, such that the reagent layer can be seen from the exterior. The reagent layer comprises a region for spreading the plasma and/or the serum, which has been separated by the blood constituent separating section from the blood sample, and a reagent supporte donor in the spreading region, the reagent undergoing a reaction with the plasma and/or the serum and forming a color as a result of the reaction.