Heparin-induced thrombocytopenia: temporal pattern of thrombocytopenia in relation to initial use or reexposure to heparin.
OBJECTIVE
Heparin-induced thrombocytopenia (HIT) is an immune-mediated adverse drug reaction associated with a decrease of platelet counts that usually begins after at least 5 days of heparin treatment. Uncertainty exists about the risk of early onset of HIT (ie, < 5 days) in relation to previous heparin exposure. We therefore analyzed the temporal pattern of thrombocytopenia in patients with laboratory-confirmed HIT to assess whether patients with previous heparin exposure have an increased risk of early onset of HIT.


METHODS
Platelet count patterns in patients with a laboratory-confirmed diagnosis of HIT were examined in a retrospective chart review of a clinical study database. The onset of thrombocytopenia < 100 x 10(9)/L associated with the current heparin treatment (mainly unfractionated heparin) was analyzed using nonparametric maximum likelihood estimation.


RESULTS
A total of 119 patients with 125 treatment episodes were assessed: HIT developed in 79 patients during initial exposure to heparin, and in 46 patients during reexposure. Early onset (< 5 days) of thrombocytopenia was associated with very recent heparin exposure. Patients reexposed to heparin within 3 months had an earlier onset of thrombocytopenia as compared to patients reexposed to heparin after 3 months (4.9 +/- 4.4 days vs 11.5 +/- 5.5 days [mean +/- SD], p = 0.001). There was no difference between onset on thrombocytopenia < 100 x 10(9)/L in patients reexposed to heparin within 3 to 12 months and after 1 year (9.7 +/- 6.4 days vs 12.3 +/- 5.2 days, p = 0.41). Whether platelet counts were obtained daily or less regularly did not affect the analysis.


CONCLUSIONS
Early onset of thrombocytopenia in HIT is associated with recent heparin treatment (< 3 months). In contrast, for patients who did not receive heparin within the previous 3 months, HIT is an unlikely explanation for thrombocytopenia that occurs within the first 5 days.
Lubenow
Norbert
N
Department of Immunology and Transfusion Medicine, Ernst-Moritz-Arndt University, Greifswald, Germany.
Kempf
Reiner
R
Eichner
Angelika
A
Eichler
Petra
P
Carlsson
Lena E
LE
Greinacher
Andreas
A
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000925:Anticoagulants / Q000009:adverse effects*; D005260:Female; D006495:Heparin, Low-Molecular-Weight / Q000009:adverse effects*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010976:Platelet Count; D012042:Registries; D012189:Retrospective Studies; D013921:Thrombocytopenia / Q000139:chemically induced*
D000925:Anticoagulants; D006495:Heparin, Low-Molecular-Weight