Hematology
Anemia
Classify by MCV, then use the reticulocyte count to separate underproduction from destruction or loss. Iron deficiency gives low ferritin, low transferrin saturation, and high TIBC - but ferritin is an acute-phase reactant and may be normal in inflammation. Anemia of chronic disease shows low TIBC, low saturation, and normal-to-high ferritin. B12 deficiency can cause neurologic findings with a normal MCV; check methylmalonic acid when suspicion persists despite borderline B12. Hemolysis produces elevated LDH and indirect bilirubin, low haptoglobin, and reticulocytosis; obtain a direct Coombs test.
Platelets and coagulation
Isolated thrombocytopenia with schistocytes, renal failure, fever, and neurologic signs is TTP - start plasma exchange urgently and avoid platelet transfusion. Heparin-induced thrombocytopenia occurs 5–10 days after exposure with a falling platelet count and thrombosis; stop heparin and use argatroban or fondaparinux. A prolonged aPTT that corrects with a mixing study suggests factor deficiency; failure to correct suggests an inhibitor.
Malignancy and emergencies
Multiple myeloma presents with CRAB features: hypercalcemia, renal failure, anemia, bone lesions with a monoclonal spike. Neutropenic fever requires cultures and empiric antipseudomonal antibiotics within 60 minutes. Transfuse at 7 g/dL generally, 8 g/dL with cardiac disease.
Worked example
A patient with platelets 30,000, schistocytes, creatinine 2.5, and confusion has TTP: order urgent plasma exchange and ADAMTS13; do not give platelets.