Decreased production of platelets: meds (bactrim, linezolid, penicillin, other), toxins, alcohol, infection (Parvo, HIV, TB, EBV), malignancy (e.g. leukemia, MDS), aplastic anemia, nutritional deficiencies (e.g. low B12)
Increased destruction: Meds (heparin, H2 blockers, NSAIDs, Vanco, Quinine, other), ITP, HIV, post viral
Consumption: HUS, TTP, DIC, HELLP
Sequestration: Splenomegaly (e.g. w/portal hypertension)
Spontaneous mucocutanous bleeding → gums, nosebleeds, GI tract
Excessive bleeding w/menstruation, following routine dental care or minor trauma
Spontaneous ecchymoses
Mucosal hemorrhages
First make sure that the thrombocytopenia is "real" and not pseudothrombocytopenia from clumping related to EDTA in tube (have re-drawn in a citrate or heparin containing tube).