A B S T R A C T Plasma fibrinopeptide (28 patients) or rapid FPA generation (>1 pmol/ ml per min) (33 patients). Slow FPA generation was found in 10/10 patients with venous thrombosis, in 4/4 with aortic aneurysm, and in several patients with acquired hypofibrinogenemia. In one such patient, addition of fibrinogen resulted in rapid FPA generation whereas thrombin addition was without effect. Rapid FPA generation was generally linear, was usually associated with slower fibrinopeptide B generation and was inhibited by parenteral or in vitro heparin. It is thought to reflect increased thrombin activity and was seen in patients with pulmonary embolism, active systemic lupus erythematosus, renal transplant rejection, and after infusion of prothrombin concentrates. The initial rate of FPA cleavage by thrombin at fibrinogen concentrations from 0.05 to 4 mg/ml showed little change between 2 and 4 mg/ml with a Km of 2.99 ,uM. At a fibrinogen concentration of 2.5 mg/ml the FPA cleavage rate was 49.2±+1.6 nmol/ml per min per U of thrombin. Exogenous thrombin added to normal blood generated 21.7 nmol/ml per U of Dr.

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A 68‐year‐old woman patient presented with laryngeal stridor. Following emergency tracheostomy, a diagnosis of acute myelocytic leukemia was made. The patient died shortly thereafter. Autopsy revealed the typical distribution and cytologic character of the leukemic process with the exception of the severe leukemic infiltration of the larynx. A review of previously reported cases indicates the need for early recognition and prompt treatment of this manifestation.

Specific radioimmunoassays were used to study fibrinopeptide cleavage from fibrinogen. Thrombin cleaves fibrinopeptide A (FPA) more rapidly than fibrinopeptide B (FPB) whereas plasmin cleaves a peptide with FPB immunoreactivity much more rapidly than FPA. Clinical blood samples manifested several distinct patterns of fibrinopeptide release (mean values in table).The elevated FPA level is interpreted as signifying increased thrombin action in vivo. A rapid FPA generation rate is thought to signify a uniformly elevated blood thrombin concentration whereas a low FPA generation rate in the presence of an elevated FPA level is thought to signify localized thrombin action. Elevated FPB immunoreactivity is postulated to reflect excessive plasmin action on fibrinogen.