Ninety-five of 322 patients were found to have diminished plasma fibrin stabilizing factor (FSF) activity as measured by a modification of a threshold assay method.

Repeat assays were normal in 85 of these 95 specimens after the addition of cysteine or other sulfhydryl-containing compounds to the plasma, suggesting that FSF was inactive in these instances.

Abnormal specimens obtained from six patients with acute granulocytic leukemia, and three obstetrical patients with hypofibrinogenemia had decreased concentrations of FSF since the repeated assays were normal after 6 hours of incubation but not after the addition of cysteine. One abnormal specimen obtained from a severe cirrhotic in hepatic coma failed to show normal FSF activity after the addition of cysteine, after incubation and after mixing with equal volumes of normal plasma. This suggested the presence of an inhibitor of FSF. No specific correlation could be made between diminished FSF activity and hemorrhagic symptoms.

It is proposed that normal hepatic function is necessary for the activation of FSF or for the removal of an inhibitor.

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