Neutrophil and Monocyte Counts in Heparin-Induced Thrombocytopenia

Heparin-induced thrombocytopenia (HIT) antibodies activate platelets, monocytes and neutrophils. Despite these findings, it is unknown whether white blood cell (WBC) counts, including neutrophils and monocytes, are altered during HIT.

We evaluated changes in total WBC counts (including WBC subsets), in 50 post-cardiac surgery patients with serologically confirmed HIT (30 patients with HIT-associated thrombosis). Daily leukocyte counts were compared with those measured one day prior to HIT onset; WBC increases were classified as mild (20.0-49.9%), moderate (50.0-99.9%) or major (≥ 100% increase). We also compared changes in WBC counts in HIT patients with and without HIT-associated thrombosis, and non-HIT patients with thrombosis.

Most (34/50 [68.0%]) patients with HIT developed WBC count increases (mild, 35.3%; moderate, 44.1%; major, 20.6%). The peak WBC count occurred on day 4 (median) of HIT, which corresponded to day 10 (median) post-surgery. Absolute neutrophil counts increased in most patients (38/50 [76.0%]); whereas absolute monocyte counts rose in some patients, the overall tendency was for the monocyte count to decrease during HIT. Unexpectedly, we found that the increase in total WBC counts, as well as in neutrophils, was seen mainly in patients who developed HIT-associated or non-HIT-associated thrombosis; in contrast, no difference in monocyte levels was seen in patients with or without thrombosis.

Leukocytosis and neutrophilia are commonly observed in patients with HIT, particularly in patients with HIT-associated thrombosis, as well as non-HIT patients with thrombosis. Thus, leukocytosis/neutrophilia should not infer automatically a diagnosis of infection or inflammation, when evaluating thrombocytopenia in heparin-exposed patients.