Risk Prediction of Heparin Induced Thrombocytopenia and Thrombosis in the Tertiary Care Setting.

Background: Heparin induced thrombocytopenia (HIT) is a challenging diagnosis; especially post cardiac surgery and patients with cardiac support devices. The diagnosis is based on clinicopathologic findings including pertinent clinical history, and heavy reliance on laboratory testing (Heparin PF-4 ELISA) to detect antibodies immunologically or by functional means (serotonin release assay - SRA). Experience with routine measurement of SRA in combination with HPF4 in this setting is limited.

Aim: To determine the clinical and laboratory findings most predictive of thrombosis in patients with HIT.

Patients and Methods: This is a retrospective analysis where we reviewed data on patients who had a positive heparin antibody thrombocytopenia from 1/1/06 to 5/1/07 at the Texas Heart Institute in Houston. We evaluated their diagnosis, O.D., SRA, Doppler ultrasound and platelet count.

Results: Our study found 52 (12.5%) out of 416 patients with positive heparin antibody. Thirty-two patients (62%) with positive heparin antibody had undergone a cardiac procedure within last 30 days. Sixteen (31%) out of the 52 patients with positive heparin antibody had thrombosis confirmed by Doppler/Ultrasound study. Of those 16 patients, 12 (80%) had undergone a cardiac procedure and 10 (63%) had their platelets drop below 75,000. Mean O.D. in patients with thrombosis was 1.10 versus 0.82 for patients with no thrombosis (p=0.14). Serotonin Release Assay (SRA) was considered positive if the serotonin release was > or = 20%. It was positive in only 5 (10%) patients, however, 3 out of those 5 patients had thrombosis. Mean O.D. for patients with positive SRA were 1.88 as compared to O.D. of 0.81 (P<0.001) in patients without positive SRA. All 5 patients had undergone a cardiac procedure.

Conclusion: Our study found almost one third of patients with positive HPF4 antibody developed thrombosis. Patients with thrombosis were more likely to have a positive SRA, higher O.D. and more likely to have undergone a cardiac procedure. Prospective studies are planned to further delineate the relationship between O.D., SRA and thrombosis in the setting of cardiac procedures.