What conditions can decrease platelet count?

Conditions That Decrease Platelet Count

Thrombocytopenia results from four primary mechanisms: decreased bone marrow production, increased platelet destruction (immune or non-immune), splenic sequestration, or dilution, with specific conditions identifiable through systematic evaluation of clinical context, laboratory findings, and peripheral blood smear examination. 1, 2, 3

Decreased Platelet Production

Bone Marrow Disorders

• 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 4
• Myelofibrosis disrupts normal marrow architecture, reducing effective platelet production 1

Viral Infections

• 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
• Other viral infections (EBV, CMV, parvovirus B19) can transiently suppress platelet production 1, 5

Nutritional and Toxic Causes

• Vitamin B12 and folate deficiency impair megakaryocyte maturation, typically presenting with macrocytic anemia alongside thrombocytopenia 5
• Alcohol toxicity directly suppresses megakaryopoiesis and causes thrombocytopenia that resolves with abstinence 5, 6
• Chemotherapy and radiation predictably reduce platelet production through cytotoxic effects on bone marrow 4, 5

Inherited Thrombocytopenias

• 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

Increased Platelet Destruction

Immune-Mediated Destruction

Primary Immune Thrombocytopenia (ITP)

• Primary ITP is an autoimmune disorder with immunologic destruction of otherwise normal platelets, diagnosed by exclusion after ruling out secondary causes 1, 2
• Diagnosis requires isolated thrombocytopenia with normal physical examination except for bleeding manifestations; presence of splenomegaly, hepatomegaly, or lymphadenopathy suggests secondary causes 1, 2

Secondary Immune Thrombocytopenia

• Autoimmune diseases (systemic lupus erythematosus, rheumatoid arthritis) cause immune-mediated platelet destruction 1, 5
• Antiphospholipid syndrome causes thrombocytopenia associated with thrombosis rather than bleeding, distinguishing it from typical ITP 4, 1
• Common variable immune deficiency (CVID) can present with ITP as an initial manifestation 1
• Lymphoproliferative disorders (chronic lymphocytic leukemia, lymphomas) cause secondary immune thrombocytopenia 1, 5
• H. pylori infection causes thrombocytopenia through immune mechanisms; eradication therapy can resolve thrombocytopenia 1

Drug-Induced Thrombocytopenia

• 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, 5, 6

Non-Immune Destruction

Thrombotic Microangiopathies

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

Pregnancy-Related Thrombocytopenia

• Gestational thrombocytopenia is the most common cause in pregnancy, presenting with mild thrombocytopenia (platelet count >70,000/μL) 1
• Preeclampsia and HELLP syndrome (hemolysis, elevated liver enzymes, low platelets) cause thrombocytopenia requiring urgent delivery 1, 5

Mechanical Destruction

• Cardiopulmonary bypass (CPB) and extracorporeal membrane oxygenation cause platelet consumption and dysfunction 4, 6
• Intra-aortic balloon counterpulsation causes mechanical platelet destruction 4
• Prosthetic heart valves cause chronic low-grade platelet consumption 6

Splenic Sequestration

• Cirrhosis and portal hypertension cause splenomegaly with platelet sequestration, typically maintaining platelet counts >50,000/μL 5
• Splenic enlargement from any cause (lymphoma, storage diseases, portal vein thrombosis) sequesters up to 90% of circulating platelets 5, 7

Dilutional Thrombocytopenia

• Massive transfusion (>10 units packed red blood cells in 24 hours) dilutes platelet concentration 4, 5
• Perioperative hemodilution from crystalloid and colloid administration reduces platelet count, particularly after cardiac surgery 4

Special Populations

Cyanotic Congenital Heart Disease

• Polycythemia and hyperviscosity in cyanotic CHD trigger platelet consumption through DIC-like mechanisms, with platelet counts inversely correlating with hematocrit levels 4
• Mild thrombocytopenia (100,000-150,000/μL) occurs more commonly than severe thrombocytopenia (<50,000/μL) in this population 4
• Platelet survival decreases to <80 hours (normal 80-130 hours) with increased fibrinolysis evidenced by elevated D-dimers 4

Renal Failure

• Uremia causes platelet dysfunction and mild thrombocytopenia through multiple mechanisms, improved with dialysis and erythropoietin 6

Myeloproliferative Disorders

• Essential thrombocythemia, polycythemia vera, and primary myelofibrosis paradoxically can present with thrombocytopenia despite being clonal platelet disorders, particularly in advanced disease 6

Critical Diagnostic Pitfalls to Avoid

• 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, 3
• 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, 5
• 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