Studies of Platelet Function as a Guide to the Severity of Thrombocytopenic Purpura and the Possible Mechanism of Purpura and Hæmorrhage

SUMMARY Abnormal results from 121 tests of platelet thromboplastic function were recorded in 30 patients with thrombocytopenic purpura of various types. The presence and degree of hemorrhage or purpura, and the platelet count were also recorded at the time the platelet function tests were performed. The results showed that when the platelet thromboplastic function was below 12%, all patients were frankly bleeding ; when it was between 12% and 25%, some patients were hemorrhagic, while others showed purpura only ; when it was above 25%, virtually nc patients were haemorrhagic. Purpura occurred over the range 25% to 53% platelet thromboplastic function. There was very little correlation between the degree of hemorrhage and platelet function, and between platelet numbers and the occurrence of purpura and hæmorrhage. It is thought that purpura is a manifestation of vascular endothelial damage, but that hemorrhage follows only when the coagulation mechanism is severely deranged by platelet dysfunction. The test of platelet thromboplastic function has proved useful in the assessment of the severity of thrombocytopenic purpura and in predicting the occurrence of hæmorrhage.