Levels of factor IX:C and factor IX:Ag were measured in 120 healthy subjects with an age range of 1 to 67 years. Levels of factor IX:C were lowest in prepubertal subjects, then reached a plateau in early adult life with a secondary increase in later adult life (> 45 years). Changes in factor IX:Ag showed a similar trend. Factor IX:Ag disproportionately increased in early adult life, however, with a less pronounced increase in later life, resulting in peaking of the ratio in early adult life. It is suggested that caution be exercised in interpreting low normal factor IX:C levels in prepubertal children, and that interpretation of ratios of antigenic to coagulant activity may need to take subject age into consideration.

The method of sample collection and time interval from venipuncture to test performance is considered to be important in platelet function testing. Platelet function studies can be performed in whole blood with the use of an impedance lumi-aggregometer, and an examination of the influence of these variables on the outcome of such a study is important. Twelve healthy donors had blood drawn with the use of conventional approach for platelet function testing and a Vacutainer method. Platelet function studies were performed at three time points over a three-hour period. No significant differences in results were observed between the methods of collection and the time to test performance. It is concluded that for platelet function screening in whole blood, with the use of an impedance lumi-aggregometer, a Vacutainer sample maintained at room temperature and tested within three hours is satisfactory.

Twenty plateletpheresis components were harvested from 11 healthy donors and stored in polyolefin bags on a horizontal flatbed agitator at 22 degrees C. After 24 hours, white cells were reduced in one aliquot by centrifugation while the other aliquot was stored unaltered. Samples were obtained aseptically from each of these platelets at intervals for up to 10 days, and measurements were made of platelet glycoprotein Ib (GPIb) by both flow cytometry and polyacrylamide gel electrophoresis, of ristocetin-induced platelet aggregation by impedance aggregometry, and of plasma and platelet von Willebrand factor (vWF) by enzyme-linked immunosorbent assay. Storage of platelets under these conditions was associated with only minor decreases in surface GPIb, intraplatelet vWF, and ristocetin-induced platelet aggregation, and no differences were observed between the white cell-reduced and nonreduced aliquots. No benefit of white cell reduction in such components before prolonged storage is evident in the vWF-platelet interaction.

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