Haematology
Anaemia
Classify by MCV and use the reticulocyte count to separate underproduction from loss or haemolysis. Iron deficiency gives low ferritin, low MCV, high TIBC and high RDW; anaemia of chronic disease gives normal or high ferritin with low TIBC and low transferrin saturation. Ferritin is an acute phase reactant, so a normal value during inflammation does not exclude iron deficiency - check transferrin saturation. B12 deficiency is macrocytic with neurological signs; never give folate alone without excluding B12 deficiency.
Haemolysis and marrow disease
Haemolysis shows raised LDH and indirect bilirubin, low haptoglobin and reticulocytosis; the direct antiglobulin test distinguishes immune from non-immune causes. Myeloma presents with hypercalcaemia, renal impairment, anaemia and bone lesions; send serum electrophoresis and free light chains, and avoid NSAIDs.
Platelets and clotting
Thrombotic thrombocytopenic purpura shows schistocytes and neurological or renal features with low ADAMTS13 - treat with plasma exchange and do not transfuse platelets. Heparin-induced thrombocytopenia is suspected from the 4Ts score; stop heparin and use argatroban. Disseminated intravascular coagulation prolongs PT and APTT with low fibrinogen and high D-dimer.
Trap: giving platelets in TTP, and delaying antibiotics in neutropenic sepsis (give them within one hour).
Rule of thumb: major bleeding on warfarin is reversed with prothrombin complex concentrate plus intravenous vitamin K, not vitamin K alone.