Activated partial thromboplastin time. A multicenter evaluation of 11 reagents in the screening of mild haemophilia A

Abstract

An internationally standardized preparation and 10 commercial kits widely used to perform the activated partial thromboplastin time (APTT) were compared in 4 laboratories for the purpose of assessing their ability to detect mild deficiencies of factor VIII activity. The participating laboratories were asked to carry out with each APTT reagent quadruplicate readings of 3 coded lyophilized plasmas containing varying levels of factor VIII (109, 26 and 17 U/dl respectively). An analysis of variance of clotting times showed significant differences between reagents and laboratories. All the reagents detected the abnormality of the plasma containing 17 U/dl, whereas a number of failures were found when the plasma with 26 U/dl was tested. When analysis of variance was carried out on ratios of factor-VIII deficient to normal plasma clotting times, the results showed less difference between laboratories and reagents. Clotting times of plasma with normal factor VIII level (109 U/dl) usually fell within the normal range indicated by manufacturers of the commercial reagents.