Screening frequency, incidence and pattern of heparin-induced thrombocytopenia syndrome at a large tertiary institution.

Increasing awareness and availability of tests for anti-PF4/heparin complex antibodies has raised concerns about indiscriminate testing and inappropriate diagnosis of heparin-induced thrombocytopenia. A retrospective review of HITS testing at a large tertiary centre was performed to determine test patterns and incidence of HITS. Records of anti-PF4 tests over 4 years were reviewed. Positive results were matched against patient medical records and records of heparin utilisation for the diagnosis of HITS. Total of 33,308 patients (9.89 % of admissions) were exposed to at least 1 day of unfractionated heparin (UFH) or low molecular weight heparin (LMWH). Of 346 anti-PF4 antibody assays performed, 52 (15 %) were positive. Seventeen patients (4.9 % of total) were determined to have HITS. Of these, 13 cases (76 %) were patients who were initiated on haemodialysis via central venous catheters. Five patients (29 %) subsequently experienced thrombosis. The rate of HITS in patients given UFH was 0.33 %. HITS occurred in only one patient given LMWH. Of 1337 patients with chronic renal failure initiated on long term haemodialysis, the incidence of HITS was 0.97 %. Despite increased awareness of HITS, testing frequency remains conservative. An overwhelming majority of HITS cases were diagnosed among patients initiated on haemodialysis.