Platelet activation in preeclampsia

Platelet activation was assessed in hospitalized third-trimester patients with preeclampsia (n = 11) or chronic hypertension with superimposed preeclampsia (n = 11) and in healthy outpatient pregnant controls (n = 10) by measuring plasma β-thromboglobulin, platelet factor 4, the platelet aggregate ratio, and the amount of collagen required to produce half-maximal aggregation velocity (K_d). Only plasma β-thromboglobulin levels differed significantly between patients with preeclampsia (50.1 ± 37.9; p < 0.05) or chronic hypertension with superimposed preeclampsia (47.6 ± 16.3; p < 0.01) and the control subjects (22.5 ± 11.3). β-Thromboglobulin values in patients with preeclampsia, but not chronic hypertension with superimposed preeclampsia, correlated directly with 24-hour urinary protein loss (r = 0.93, p < 0.001) and serum creatinine levels (r = 0.62, p < 0.05) and inversely with creatinine clearance (r = 0.60, p = 0.05). We conclude that (1) β-thromboglobulin is elevated in patients with preeclampsia or chronic hypertension with superimposed preeclampsia, (2) the normal platelet aggregate ratio and the K_d indicate that the increase in β-thromboglobulin is not due to an intrinsic change in platelet responsiveness, and (3) the elevation of β-thromboglobulin in patients with either preeclampsia or chronic hypertension with superimposed preeclampsia appears to be secondary to platelet consumption in the microvasculature, although in patients with preeclampsia altered renal function may be contributory.