Age-dependent effect on the level of factor IX.

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.

Intraplatelet von Willebrand factor and ABO blood group.

Levels of plasma Von Willebrand Factor (vWF) are known to be influenced by ABO Blood Group but such an influence on platelet vWF is not known. Forty-three healthy donors had blood drawn for measurement of plasma and platelet vWF, both antigenic (vWF:Ag) and functional (RCo). Twenty-six were Group O and seventeen were Group A. Groups did not differ in age, platelet count, hemoglobin, white cell counts, platelet rich plasma counts nor length of in vitro storage of samples prior to assay. Plasma levels of vWF:Ag and RCo was lower in Group O as expected. Platelet RCo was lower in Group O and such a trend was present for vWF:Ag. This influence of ABO Groups on platelet vWF was modest compared to that on plasma vWF.

Effects of prestorage white cell-reduction of apheresis platelets on platelet glycoprotein Ib and von Willebrand factor.

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.

Hemostatic effects of salsalate in normal subjects and patients with hemophilia A.

Salsalate in a non-acetylated salicylate with activity as an antirheumatic agent. The hemostatic effects of this agent were studied in twelve healthy subjects and nine patients with hemophilia A. Healthy subjects showed no change in bleeding time, platelet aggregation response to adenosine diphosphate (ADP) or collagen, or adenosine triphosphate (ATP) release in response to arachidonic acid as measured in an impedance whole blood lumi-aggregometer. The patients with hemophilia A showed no bleeding time prolongation nor an effect on ADP or collagen induced platelet aggregation in platelet rich plasma. It is concluded that this agent may be useful in the treatment of arthritis in patients with hereditary coagulation disorders.

von Willebrand's variant (type II Buffalo). Thrombocytopenia after desmopressin but absence of in vitro hypersensitivity to ristocetin.

Von Willebrand's disease is categorized into types and subtypes based on multimeric analysis of plasma von Willebrand's factor. Such categorization is of value because both the mode of inheritance and the choice of therapeutic material differ between subtypes. The Type IIB variant is characterized by hypersensitivity in vitro to ristocetin and thrombocytopenia after administration of desmopressin (DDAVP). Hypersensitivity to ristocetin has also been described in Type I variants but without thrombocytopenia after DDAVP. This report describes a new Type II variant characterized by the converse situation, absence of hypersensitivity to ristocetin in vitro but transient thrombocytopenia after intravenous administration of DDAVP.

Whole blood aggregometry. Influence of sample collection and delay in study performance on test results.

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.

Whole blood aggregation in von Willebrand disease.

Platelet function testing in von Willebrand disease is generally performed in platelet rich plasma using an optical system. The characteristic abnormality is an abnormal response to the agglutinating agent, ristocetin. Platelet aggregation can be also studied in whole blood using either an impedance aggregometer or a particle counter. Fifteen patients with von Willebrand disease and fifteen normal subjects were studied using both whole blood methods. In the impedance system, normal subjects responded to ristocetin (1 mg/ml) with short lag phases (less than 70 sec) and normal maximum aggregation greater than 5 omega). Only three patients with von Willebrand disease responded with normal maximal aggregation but each of these had a prolonged lag phase, and this may be a useful diagnostic parameter. In the particle counter, discrimination between normals and some von Willebrand disease patients was possible but an overlap between normals and von Willebrand patients is evident. It is concluded that the platelets in patients with von Willebrand disease exhibit the same abnormalities in whole blood as in platelet rich plasma and that the combination of impedance aggregometry and a factor VIII procoagulant assay is a time-efficient and sensitive method to screen for von Willebrand disease.

Platelet function and ABO blood group.

An influence of the ABO blood group on von Willebrand and Factor VIII:C levels is known. Von Willebrand factor interacts with at least two platelet membrane receptors, but the effect of ABO group on platelet function is an unstudied area. The authors examined platelet function in 40 plateletpheresis donors using an impedance lumi-aggregometer. Aggregation responses to collagen, adenosine diphosphate (ADP), and ristocetin were measured and the adenosine triphosphate (ATP) release to thrombin. Twenty donors were Group O and 20 were Group A. Measurements of von Willebrand factor antigen (vWf:Ag), Factor VIII: C, and ristocetin co-factor (RiCoF) in the same group showed reduced levels of vWf:Ag and Factor VIII:C in Group O, as previously reported. The aggregation response to collagen and ADP and the release of ATP did not differ. The aggregation response to ristocetin, however, was better in Group O than in Group A despite the lower vWf:Ag levels. The explanation for this is unclear, but the data suggest an influence of blood group antigens on the interaction between von Willebrand's factor and platelets.