Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (304 page)

   RBC: profound anemia, microcytosis, reduced MCV and MCHC, very elevated RDW. Hb levels may be as low as 3–4 g/dL. The anemia may become acutely life threatening during
aplastic crises
, mostly provoked by infection with parvovirus B19, which infects precursor erythroid cells.

   Red cell morphology shows extreme hypochromia and poikilocytosis, tear drop cells, and many target cells. Heinz bodies are readily identified when the smears are stained with supravital stains.

   WBC is elevated (in part falsely so, due to enumeration of nucleated RBCs as WBCs by some automated counters), but true leukocytosis is usually present.

   Platelets may be reduced due to hypersplenism but become elevated in splenectomized patients.

   Peripheral blood smear (PBS): marked poikilocytosis with many target cells, tear drop cells, nucleated RBCs, and basophilic stippling of RBCs.

   Reticulocyte count is inappropriately low, in part the result of ineffective erythropoiesis. It may become 0 during aplastic crises.

   Bone marrow aspirate shows red cell hyperplasia with marked shift to early red cell progenitors due to intramedullary hemolysis, in turn the result of accelerated apoptosis. Megaloblastic morphology may be observed in the absence of folate supplements. Extramedullary hematopoiesis develops in the skeletal bones, liver, and spleen.

   Hb variant analysis shows absence of HbA1 in β(0) thalassemia, where only HbA2 and HbF are present. HbA2 may increase to 3–6% (unless iron deficiency is also present). HbA1 is present after RBC transfusions.

   Serum iron and ferritin increase progressively throughout life due to RBC transfusions.

   Serum bilirubin is elevated.

   Liver function tests are abnormal, in part the result of transfusional viral hepatitis. This problem is becoming rare with present-day transfusion practice.

   LDH and uric acid are elevated.