title: The timing of a positive test result for heparin-induced thrombocytopenia relative to the platelet count and anticoagulant therapy in 43 consecutive cases.
abstract: We studied the timing of a positive heparin-induced thrombocytopenia (HIT) test result relative to changes in platelet count and anticoagulant use. We obtained platelet counts in 100 consecutive HIT+ cases before, during, and after heparin therapy; 43 cases met study criteria and were included in study part 1. In part 2, platelet counts at the time of the HIT test in 2 groups (100 each HIT+ and HIT- cases) were compared. In part 1, cases could be divided into 4 groups based on the diagnosis of HIT relative to platelet counts (1, within 1-2 days of a major drop in platelet count [11.6%]; 2, after > 2 days of a major fall in platelet count [41.9%]; 3, in patients with already low platelet counts [27.9%]; 4, after platelet count was rising [18.6%]). In study part 2, the mean platelet counts for the HIT+ and HIT- groups were almost identical. HIT should be suspected in any thrombotic patient who had a previous decline in platelet count, has a low platelet count, or has a rising platelet count after a previous decline in association with heparin exposure. In study part 2, 1 platelet count value at the time of the HIT test did not provide useful information.
authors.affiliation: Division of Laboratory Medicine, Department of Pathology, Massachusetts General Hospital, Harvard Medical School, Boston, USA.
authors.forename: Majed A
authors.initials: MA
authors.lastname: Refaai
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Van Cott
authors.forename: Michael
authors.initials: M
authors.lastname: Laposata
mesh_terms: D000925:Anticoagulants / Q000009:adverse effects*; D001792:Blood Platelets / Q000187:drug effects*; D006493:Heparin / Q000009:adverse effects*; D006801:Humans; D010976:Platelet Count; D012189:Retrospective Studies; D013921:Thrombocytopenia / Q000097:blood / Q000139:chemically induced* / Q000517:prevention & control; D013927:Thrombosis / Q000150:complications* / Q000517:prevention & control; D013997:Time Factors
chemical_list: D000925:Anticoagulants; D006493:Heparin