Higher optical density of an antigen assay predicts thrombosis in patients with heparin-induced thrombocytopenia.
OBJECTIVE
To correlate optical density and percent inhibition of a two-step heparin-induced thrombocytopenia (HIT) antigen assay with thrombosis; the assay utilizes reaction inhibition characteristics of a high heparin concentration.


METHODS
Patients with more than 50% decrease in platelet count or thrombocytopenia (<150 x 10(9)/L) after exposure to heparin, who had a positive two-step antigen assay [optical density (OD) >0.4 and >50 inhibition with high concentration of heparin] were included in the study.


RESULTS
Forty of 94 HIT patients had thrombosis at diagnosis; 54/94 had isolated-HIT without thrombosis. Eight of the isolated-HIT patients developed thrombosis within the next 30 d; thus, a total of 48 patients had thrombosis at day 30. At diagnosis there was no significant difference in OD between HIT patients with thrombosis and those with isolated-HIT. However, OD was significantly higher in all patients with thrombosis (n = 48, 1.34 +/- 0.89), including isolated-HIT patients who later developed thrombosis within 30 d (n = 8, 1.84 +/- 0.64) as compared to isolated-HIT patients who did not develop thrombosis (0.96 +/- 0.75; P = 0.011 and P = 0.008). The Receiver Operative Characteristic Curve showed that OD >1.27 in the isolated-HIT group had a significantly higher chance of developing thrombosis by day 30. None of these groups showed significant difference in percent inhibition. Multivariate analysis showed a 2.8-fold increased risk of thrombosis in females. Similarly, thrombotic risk increased with age and OD values.


CONCLUSIONS
Higher OD is associated with significant risk of subsequent thrombosis in patients with isolated-HIT; percent inhibition, however, was not predictive.
Altuntas
Fevzi
F
Department of Pathology, The University of Texas Southwestern Medical Center, Dallas, TX 75390-9073, USA.
Matevosyan
Karen
K
Burner
James
J
Shen
Yu-Min
YM
Sarode
Ravindra
R
D000368:Aged; D000941:Antigens / Q000097:blood* / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006493:Heparin / Q000009:adverse effects*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D013921:Thrombocytopenia / Q000139:chemically induced* / Q000150:complications*; D013927:Thrombosis / Q000139:chemically induced* / Q000150:complications*
D000941:Antigens; D006493:Heparin