Heparin-Induced Thrombocytopenia (HIT): Type 1 vs. Type 2

Type 1: Heparin directly causes platelets to aggregate (non-immune). Occurs within 48hrs after initiating heparin; mild, transient and no treatment needed.

Type 2: Heparin induces auto-immune mediated response (antibodies formed against heparin bound to platelet factor 4 (PF4). Characterized by the  4T score. (If the score is 0-3, HIT is unlikely, <5%)  

NOTE: HIT is generally not marked by bleeding; instead an increased risk of venous thromboembolism!

REFERENCES

1. Warkentin, T. E. (2003), Heparin-induced thrombocytopenia: pathogenesis and management. British Journal of Haematology, 121: 535–555. doi:10.1046/j.1365-2141.2003.04334.x
2. Warkentin TE, Heddle NM (March 2003). “Laboratory diagnosis of immune heparin-induced thrombocytopenia”. Curr Hematol Rep. 2 (2): 148–57.
3. Greinacher, A., Michels, I., Schafer, M., Kiefel, V. & Mueller- Eckhardt, C. (1992) Heparin-associated thrombocytopenia in a patient treated with polysulphated chondroitin sulphate: evidence for immunological crossreactivity between heparin and polysulphated glycosaminoglycan. British Journal of Haematology, 81, 252–254.