Vacutainer sampling for blood coagulation assays

Abstract

Plasma samples obtained by means of evacuated tubes and with venous cannula were compared with regard to the effect on five plasma coagulation assays. The single significant difference found was not caused by sampling technique but by citrate concentration used. Evacuated tubes, siliconized and unsiliconized, with various citrate concentrations were compared regarding the effect on commercial prothrombin complex and APTT tests which showed varying sensitivity to citrate concentration. The effect on APTT could be corrected by adjustment of calcium chloride concentration. Siliconization did not significantly influence the test results. A fibrinolytic inhibitor EACA (0.076 mol/1) added to the citrate inhibited the effect of streptokinase (10-20 iu/ml blood) in vitro but also influenced several coagulation tests. Storage of blood samples for 3-4 h at room temperature in centrifuged open or uncentrifuged stoppered tubes did not appreciably influence prothrombin complex test results, but gave a prolongation of APTT which was more pronounced in open centrifuged tubes. Storage of samples in stoppered uncentrifuged tubes even resulted in a marked shortening of APTT in some samples from patients under heparin treatment. The cause of this effect is discussed. Hence storage of blood samples for APTT and similar tests should be avoided. It is concluded that evacuated tubes might be used for coagulation tests if the specimens obtained are handled correctly. Preferably one citrate concentration should be selected for use.

Key Words:

• blood coagulation tests
• evacuated tubes
• medical technology