Blood and Lymphoreticular System
Anemia by MCV
Microcytic: iron deficiency (low ferritin, high TIBC, low saturation), thalassemia (normal or high ferritin, normal TIBC, target cells, elevated HbA2 in beta trait), anemia of chronic disease (low TIBC, normal or high ferritin, low saturation), lead poisoning (basophilic stippling), sideroblastic anemia (ring sideroblasts). Normocytic: acute blood loss, hemolysis, chronic kidney disease, aplastic anemia. Macrocytic: B12/folate deficiency, alcohol, liver disease, hypothyroidism, drugs such as methotrexate or hydroxyurea, myelodysplasia. The reticulocyte index separates underproduction from loss or destruction.
Hemolysis
Elevated LDH and indirect bilirubin, low haptoglobin, elevated reticulocytes; intravascular hemolysis adds hemoglobinuria and schistocytes. Causes include G6PD deficiency (Heinz bodies, bite cells, oxidant triggers), hereditary spherocytosis (osmotic fragility, family history), sickle cell disease, autoimmune hemolysis (positive direct Coombs), and microangiopathic processes (TTP, HUS, DIC).
Coagulation
Platelet-type bleeding is mucosal, petechial, and immediate; factor-type bleeding is deep, delayed, and involves joints. PT measures factor VII and the common pathway; PTT measures VIII, IX, XI, XII and the common pathway. A mixing study that corrects indicates factor deficiency; failure to correct indicates an inhibitor such as lupus anticoagulant. DIC shows prolonged PT/PTT, thrombocytopenia, low fibrinogen, elevated D-dimer, and schistocytes.
Malignancy quick hits
Hodgkin lymphoma: Reed-Sternberg cells, CD15/CD30, contiguous spread, B symptoms. Multiple myeloma: CRAB features, rouleaux, M spike, narrowed albumin-globulin gap.
Rule of thumb
Do not diagnose iron deficiency without a low ferritin; ferritin is an acute-phase reactant and can look normal in a deficient patient who is inflamed. A high ferritin with low TIBC points to anemia of chronic disease.