Bleeding may result from abnormalities of (1) platelets, (2) blood vessel walls, or (3) coagulation. Platelet disorders characteristically produce petechial and purpuric skin lesions and bleeding from mucosal surfaces. Defective coagulation results in ecchymoses, hematomas, and mucosal and, in some disorders, recurrent joint bleeding (hemarthroses).
Normal platelet count is 150,000–350,000/μL. Thrombocytopenia is defined as a platelet count <100,000/μL. Bleeding time, a measurement of platelet function, is abnormally increased if platelet count <100,000/μL; injury or surgery may provoke excess bleeding. Spontaneous bleeding is unusual unless count <20,000/μL; platelet count <10,000/μL is often associated with serious hemorrhage. Bone marrow examination shows increased number of megakaryocytes in disorders associated with accelerated platelet destruction; decreased number in disorders of platelet production. Evaluation of thrombocytopenia is shown in Fig. 70-1.
Algorithm for evaluating the thrombocytopenic pt.
(1) Production defects such as marrow injury (e.g., drugs, irradiation), marrow failure (e.g., aplastic anemia), marrow invasion (e.g., carcinoma, leukemia, fibrosis); (2) sequestration due to splenomegaly; (3) accelerated destruction—causes include:
Drugs such as chemotherapeutic agents, thiazides, ethanol, estrogens, sulfonamides, quinidine, quinine, methyldopa.
Heparin-induced thrombocytopenia is seen in 5% of pts receiving >5 days of therapy and is due to in vivo platelet aggregation often from anti–platelet factor 4 antibodies. Arterial and occasionally venous thromboses may result. Despite the low platelets, HIT is a hypercoagulable state.
Autoimmune destruction by an antibody mechanism; may be idiopathic or associated with systemic lupus erythematosus (SLE), lymphoma, HIV.
Idiopathic thrombocytopenic purpura (ITP) has two forms: an acute, self-limited disorder of childhood requiring no specific therapy, and a chronic disorder of adults (esp. women 20–40 years). Chronic ITP may be due to autoantibodies to glycoprotein IIb-IIIa or glycoprotein Ib-IX complexes.
Disseminated intravascular coagulation (DIC)—platelet consumption with coagulation factor depletion [prolonged prothrombin time (PT), partial thromboplastin time (PTT)] and stimulation of fibrinolysis [generation of fibrin split products (FSPs)]. Blood smear shows microangiopathic hemolysis (schistocytes). Causes include infection (esp. meningococcal, pneumococcal, gram-negative bacteremias), extensive burns, trauma, or thrombosis; giant hemangioma, retained dead fetus, heat stroke, mismatched blood transfusion, metastatic carcinoma, acute promyelocytic leukemia.
Thrombotic thrombocytopenic purpura (TTP)—rare disorder characterized by microangiopathic hemolytic anemia, fever, thrombocytopenia, renal dysfunction (and/or hematuria), and neurologic dysfunction caused by failure to cleave von Willebrand factor (vWF) normally.
Hemorrhage with extensive transfusion.
Platelet clumping secondary to collection of blood in EDTA (0.3% of pts). Examination of blood smear establishes diagnosis.
Platelet count >350,000/μL. Either primary (essential thrombocytosis; Chap. 72) or secondary (reactive); latter secondary to severe hemorrhage, iron deficiency, surgery, after splenectomy (transient), malignant neoplasms (esp. Hodgkin's disease, polycythemia vera), chronic inflammatory diseases (e.g., inflammatory bowel disease), recovery from acute infection, vitamin B12 deficiency, drugs (e.g., vincristine, epinephrine). Rebound thrombocytosis may occur after marrow recovery from cytotoxic agents, alcohol, vitamin B12 replenishment. Primary thrombocytosis may be complicated by bleeding and/or thrombosis; secondary rarely causes hemostatic problems.
Disorders of Platelet Function
Suggested by the finding of prolonged bleeding time with normal platelet count. Defect is in platelet adhesion, aggregation, or granule ...