Think about thrombocytopenia in three broad categories after ruling out pseudothrombocytopenia

–Pseudothrombocytopenia (low platelet count due to clumping in EDTA tube, repeat with heparin or citrate top to confirm)

–Underproduction (anything in the BM that prevents production, usually affects other lines as well)

eg: marrow failure (aplastic anemia), nutritional deficiency (B12/folate/copper)
eg:marrow invasion-leukemia, tumor, fibrosis, granulomatous diseases like sarcoidosis)
eg:marrow injury-drugs (long list), radiation, infection (Hep C, viral, HIV), sepsis
eg:congenital (Wiskott Aldrich, Bernard Soulier)

-Splenic sequestration (anything that can cause splenomegaly. eg: cirrhosis)

-Peripheral destruction (can be broken up into immune mediated and non-immune mediated)

Etiologies of thrombocytopenias that are life-threatening and can cause thromboses in addition to bleeding-does your patient have one of these?

–HITT-need to discontinue heparin and treat with non-heparin anticoagulant (eg: direct thrombin inhibitor, Argatroban), can cause arterial and venous thromboses
–APLS– associated with both arterial and venous thromboses
–DIC-risk of bleeding and thromboses (usually venous)
-HUS-TTP-can be life-threatening if plasmapheresis is not initiated

ITP

-Acquired thrombocytopenia due to auto-antibodies against platelet antigens
-Usually ISOLATED thrombocytopenia without anemia or leukopenia
-Can be Primary or Secondary

Secondary etiologies: HIV, Hep B,C, CLL, SLE, APLS, H Pylori, thyroid disease

Treatment: 

1)Asymptomatic and platelet count >30-40k: no treatment!
2)Symptomatic: Glucocorticoids/IVIG
3)Refractory: Rituximab, TPO agonist (Eltromabag, Romiplostim), splenectomy

Comparing ITP vs. TTP vs. DIC (http://emedicine.medscape.com/article/206598-overview)