Thrombocytopenia Heparin-induced thrombocytopenia 2012-05-30T08:31:16Z A delay of 5-10 days following administration of heparin is common in patients with no previous (or remote) exposure to heparin, but the drop in platelet count may be precipitous in patients with recent exposure. Heparin-induced thrombocytopenia is caused by antibodies against platelet factor 4. SNOMEDCT_US:73397007 HP:0011874 Low platelet count following administration of unfractionated or (less commonly) low-molecular weight heparin. UMLS:C0272285