Great white sighting: a case of heparin-induced thrombosis with thrombocytosis

Background: Heparin-induced thrombocytopenia (HIT) is an immune-mediated adverse response to heparin therapy, characterized by decreased platelet count and increased risk of thrombosis. HIT, without the tell-tale sign of thrombocytopenia, has rarely been described. Key Clinical Question: Can HIT be diagnosed in the presence of thrombocytosis? What clinical clues and diagnostic tools facilitate accurate diagnosis in such cases? Clinical Approach: We report a case of HIT with thrombocytosis in a young male who initially presented after traumatic knee dislocation. HIT was diagnosed clinically through the discovery of a white thrombus during a vascular surgery procedure and corroborated by a positive latex immunoturbidimetric immunoassay (HemosIL HIT-Ab _{(platelet-factor 4(PF4)-heparin)}), a rapid immunoassay. Conclusion: With its high sensitivity, specificity, and rapid results, the latex immunoturbidimetric immunoassay is a valuable diagnostic tool, even among patients with a seemingly low pretest probability. This case underscores the guidance imparted by Dr Andreas Greinacher: “[HIT] must be considered if thrombosis occurs or progresses despite effective heparinization even in the absence of thrombocytopenia.” Access to rapid and effective laboratory testing reduces the probability of diagnostic error.