Homogeneous, single-chain human factor V was used to develop a double antibody competition radioimmunoassay to measure factor V concentrations in plasma and platelets. Standard curves were constructed that allow for the detection of as little as 20 ng factor V/ml of plasma. Normal factor V concentrations range from 4 to 14 micrograms/ml of plasma with an average value of 7.0 +/- 2.0 micrograms/ml (n = 64). No correlation was observed between antigen levels and age or sex. The radioimmunoassay data are consistent with factor V clotting assays, providing freshly drawn plasma is used in the bioassay. Radioimmunoassay of washed platelets indicate that 0.63–1.93 microgram of factor V is present per 2.5 X 10(8) platelets (4612–14128 molecules of the factor V platelet). When normalized to individual hematocrits and platelet count, the data indicated that platelets contribute approximately 18%-25% of the factor V found in whole blood. In addition, two individuals with functionally deficient factor V were examined and found to be deficient in both antigen and activity.

To define clinical and laboratory characteristics of the lupus anticoagulant (LA), we reviewed our experience (219 subjects). Subjects were divided into group A, those with the LA and the diagnosis of lupus erythematosus, group B, those with the LA but nonlupus diagnoses, and group C, those with drug-related lupus syndromes. The typical laboratory findings consisted of a prolonged and inhibited plasma clot time (an average of 1.9 times control time) which was proportionately more prolonged than the partial thromboplastin time or activated partial thromboplastin time (APTT) (average 1.3 times control). Ninety-eight percent had a prolonged plasma clot time and 94% had a prolonged partial thromboplastin time. The prothrombin and thrombin times were prolonged in 33 and 25% of subjects, respectively. Washed platelets shortened the APTT in the 22 subjects so tested. Monoclonal protein peaks were seen in 7% of patients. Seventeen episodes of bleeding were observed, but in all but one instance there was another hemostatic defect present. In the 18 patients who underwent major operations, there were no hemorrhagic complications. Fifty-eight episodes of thrombosis were observed with the same incidence in group A (25%) as in group B (26%). Bleeding is rare with the LA but thrombosis is common even without SLE and lupuslike syndromes. The plasma clot time in platelet-rich plasma is more prolonged, and in our experience, is more sensitive in detecting the lupus anticoagulant than is the partial thromboplastin time.

A coagulation Factor V inhibitor developed in a man 75 yr of age in association with an anaplastic malignancy and drug treatment (including the aminoglycoside antibiotic, gentamicin). The patient did not bleed abnormally, despite both surgical challenge and plasma Factor V activity of <1%. The inhibited plasma had grossly prolonged prothrombin and activated partial thromboplastin times, but a normal thrombin time. Mixing studies indicated progressive coagulation inhibition with normal plasma, but not with Factor V-deficient plasma, and reversal of coagulation inhibition by the addition of bovine Factor V to the patient's plasma. 1 ml of patient plasma inhibited the Factor V activity of 90 ml of normal human plasma. The inhibitor was isolated by sequential affinity chromatography on protein A-Sepharose and Factor V-Sepharose. The IgG isolate markedly inhibits the activity of prothrombinase assembled from purified Factors Xa and Va, calcium ion, and phospholipid vesicles, and partially inhibits prothrombinase assembled from purified Factor Xa, calcium ion, and normal platelets. The Factor V of platelets, however, appears relatively inaccessible to the antibody, inasmuch as platelets isolated from whole blood supplemented for 8 h with the antibody functioned normally with respect to platelet Factor V-mediated prothrombinase function. The absence of obvious hemorrhagic difficulties in the patient, the total inhibition of plasma Factor V by the inhibitor, and the apparent inaccessibility of platelet Factor V to the inhibitor specifically implicate platelet Factor V in the maintenance of hemostasis.

Thirty cases of amyloidosis with factor-X deficiency, including six of our own, were reviewed. Modest deficiency of factor X was often associated with severe bleeding. In many of the cases, clinical bleeding could not be accounted for by deficiency of factor X alone. Other hemostatic defects were found in these patients and probably contributed to the bleeding. Modes of treatment, including the empiric use of corticosteroids and splenectomy, were discussed in light of current knowledge of pathogenesis of this unusual blood clotting disorder. This involves the interaction of amyloid fibrils and blood clotting factors.

Bone marrow from a normal male pig was transplanted into a related female pig with severe homozygous von Willebrand's disease (vWd). After engraftment the circulating leukocytes were of the male karyotype, and the platelets were strongly positive for von Willebrand factor (vWF) by indirect immunofluorescence. The average level of vWF was 1.96 U/dl and of ristocetin cofactor was 2.8 U/dl. The ear immersion bleeding time before transplantation was consistently more than 15 min and afterwards varied between 5 min and more than 15 min. Transfused vWF corrected the bleeding time at a level of 10 U/dl, which is lower than that required for a von Willebrand pig. We concluded that: (a) the plasmatic compartment is only minimally replenished by the vWF from platelets and megakaryocytes; and (b) the platelet vWF alone only partially corrects the abnormal tests of the hemostatic mechanism in severe vWd.