Q: What percentage of patients may develop HIT (Heparin Induced Thrombocytopenia) with Heparin treatment?

Answer:   About 5%

Its about 5.0 percent in patients exposed to heparin for more than four days but only 0.2 percent for those treated with unfractionated heparin for less than four days.

But to note, recently some studies have suggested incidence up to 15%!

References:

1. Martel N, Lee J, Wells PS. Risk for heparin-induced thrombocytopenia with unfractionated and low-molecular-weight heparin thromboprophylaxis: a meta-analysis. Blood 2005; 106:2710.

2. Smythe MA, Koerber JM, Mattson JC. The incidence of recognized heparin-induced thrombocytopenia in a large, tertiary care teaching hospital. Chest 2007; 131:1644.

3. Oliveira GB, Crespo EM, Becker RC, et al. Incidence and prognostic significance of thrombocytopenia in patients treated with prolonged heparin therapy. Arch Intern Med 2008; 168:94.