Conditions That Decrease Platelet Count

Decreased Platelet Production

Myelodysplastic syndromes, acute leukemias, and bone marrow infiltration by malignancies impair megakaryocyte function and platelet production, requiring bone marrow examination for diagnosis 1
Aplastic anemia causes sustained severe thrombocytopenia through bone marrow failure, often presenting with pancytopenia rather than isolated thrombocytopenia 3
Myelofibrosis disrupts normal marrow architecture, reducing effective platelet production 1
HIV infection commonly causes thrombocytopenia through direct bone marrow suppression and should be tested in all adults with suspected immune thrombocytopenia 1, 2
Hepatitis C virus (HCV) causes thrombocytopenia through both bone marrow suppression and immune mechanisms, warranting testing in adults with typical ITP presentation 1
Chemotherapy and radiation predictably reduce platelet production through cytotoxic effects on bone marrow 3
Wiskott-Aldrich syndrome, thrombocytopenia-absent radius (TAR) syndrome, and MYH9-related disease affect platelet production through genetic mechanisms 1
22q11.2 deletion syndrome causes characteristically lower platelet counts with large platelets and reduced platelet quality, though usually mild 1

Primary ITP is an autoimmune disorder with immunologic destruction of otherwise normal platelets, diagnosed by exclusion after ruling out secondary causes 1, 2
Diagnosis of primary ITP requires isolated thrombocytopenia with normal physical examination except for bleeding manifestations; presence of splenomegaly, hepatomegaly, or lymphadenopathy suggests secondary causes 1, 2
Antiphospholipid syndrome causes thrombocytopenia associated with thrombosis rather than bleeding, distinguishing it from typical ITP 4, 1
H. pylori infection causes thrombocytopenia through immune mechanisms; eradication therapy can resolve thrombocytopenia 1
Heparin-induced thrombocytopenia (HIT) typically presents with moderate thrombocytopenia (30-70 G/L) occurring 5-10 days after heparin initiation, paradoxically associated with thrombosis rather than bleeding 4, 1, 2
The 4T score (thrombocytopenia degree, timing, thrombosis presence, other causes) stratifies HIT probability; scores ≥6 indicate high probability requiring immediate anti-PF4 antibody testing 4, 1, 2
GPIIb-IIIa inhibitors (abciximab, eptifibatide, tirofiban) cause early and often profound thrombocytopenia in acute coronary syndrome treatment 4
Quinidine, sulfonamides, and numerous other medications cause immune-mediated thrombocytopenia through drug-dependent antibodies 2

Thrombotic thrombocytopenic purpura (TTP) causes thrombocytopenia with microangiopathic hemolytic anemia, requiring urgent plasma exchange 4
Disseminated intravascular coagulation (DIC) causes consumption thrombocytopenia with coagulation factor depletion, elevated PT/aPTT, low fibrinogen, and elevated D-dimers 5, 4

Polycythemia and hyperviscosity in cyanotic CHD trigger platelet consumption through DIC-like mechanisms, with platelet counts inversely correlating with hematocrit levels 5
Mild thrombocytopenia (100,000-150,000/μL) occurs more commonly than severe thrombocytopenia (<50,000/μL) in this population 5
Platelet survival decreases to <80 hours (normal 80-130 hours) with increased fibrinolysis evidenced by elevated D-dimers 5

Pseudothrombocytopenia from EDTA-dependent platelet clumping occurs in 0.1% of adults; always confirm with peripheral blood smear and repeat count in heparin or citrate tube 1, 2
Post-transfusion purpura from alloimmunization causes sudden, major thrombocytopenia with hemorrhagic complications requiring specific treatment 4
Missing drug-induced thrombocytopenia by failing to obtain comprehensive medication history including over-the-counter drugs, herbal supplements, and recent antibiotic exposure 2
Overlooking inherited thrombocytopenias by not obtaining family history and examining platelet size on peripheral smear 1
Failing to recognize HIT in patients receiving heparin (including heparin flushes), particularly when thrombosis accompanies thrombocytopenia 4, 2