CAUSES OF THOMBOCYTOPENIA

I. Decreased production of platelets

1. Aplastic anemia
2. BM replacement, e.g. CLL, non-Hodgkin's lymphoma
3. Pregnancy
4. Viral illnesses, inc. HIV, EBV, Rubella
5. Drugs (heparin, quinidine, quinine, sulfonamides, zidovudine)
6. Myelodysplasia

II. Increased destruction of platelets, e.g.

1. Immune thrombocytopenia--splenic destruction

1. Idiopathic Thrombocytopenic Purpura
2. Systemic Lupus Erythematosus

2. Abnormal platelet activation, e.g. Disseminated Intravascular Coagulation
3. Thrombotic Thrombocytopenic Purpura

III. Hypersplenism, often from chronic liver dis.

IV. Qualitative platelet defects

1. Von Willelbrand's disease, which also impairs fibrinogenesis
2. Uremia
3. NSAID abuse

V. Pseudothrombocytopenia--a lab artifact due to clumping from EDTA-dependent agglutinins

VI. Thrombocytopenia in pregnancy--All of the above are possible, plus:

1. Gestational thrombocytopenia (aka incidental thrombocytopenia of pregnancy)
   1. 8% of pregnancies
   2. Usually presents in 2nd or 3rd trimester
   3. Antiplatelet Ab's are common but their significance vis-a-vis the thrombocytopenia is unknown
   4. Generally mild (platelet count us. > 70; if < 50, think ITP) and asymptomatic
   5. Platelet counts us. return to normal within 3mos after delivery
   6. Fetal/neonatal platelet count is usually normal
   7. May recur in subsequent pregnancies; recurrence risk is unknown
   8. "There are no specific diagnostic tests to distinguish...from mild ITP" (ACOG 9/99)
2. Preeclampsia and "HELLP" Syndrome--responsible for about 20% of thrombocytopenia in pregnancy
3. See section on ITP in pregnancy

VII. Neonatal thrombocytopenia

VIII. Hepatitis C