Chapter 14: Hematology
- A. General Evaluation Anemia is defined by age-specific norms (Table 14-1 and Fig. 14-1). Evaluation includes the following:
- 1. Complete history: Includes blood loss, fatigue, pica, medication exposure, growth and development, nutritional history, menstrual history, ethnic background, history of hyperbilirubinemia and family history of anemia, splenectomy, or cholecystectomy
- 2. Physical examination: Includes pallor, jaundice, glossitis, tachypnea, tachycardia, cardiac murmur, hepatosplenomegaly, and signs of systemic illness
- 3. Initial laboratory tests: May include a complete blood count with red blood cell (RBC) indices, reticulocyte count, blood smear, stool for occult blood, urinalysis, and serum bilirubin
- B. Diagnosis Anemias may be categorized as macrocytic, microcytic, or normocytic. Table 14-2 gives an approach to diagnosis based on RBC production and cell size. Note that normal ranges for hemoglobin (Hb) and mean corpuscular volume (MCV) are age dependent.
- C. Evaluation of Specific Causes of Anemia
- 1. Iron-deficiency anemia: Hypochromic/microcytic anemia with a low reticulocyte count and an elevated red cell distribution width (RDW)
- a. Serum ferritin reflects total body iron stores after age 6 months and is the first value to fall in iron deficiency; may be falsely elevated with inflammation or infection
- b. Other indicators: Low serum iron, an elevated total iron-binding capacity (TIBC), low mean cell hemoglobin concentration (MCHC), elevated transferrin receptor level, and low reticulocyte Hb content
- c. Iron therapy should result in an increased reticulocyte count in 2–3 days and an increase in hematocrit (HCT) after 1–4 weeks of therapy. Iron stores are generally repleted with 3 months of therapy
- d. Mentzer index (MCV/RBC): Index >13.5 suggests iron deficiency; Mentzer index <11.5 suggests thalassemia minor. Increased RDW also helps distinguish iron-deficiency anemia from thalassemia
- 2. Hemolytic anemia: Rapid RBC turnover. Etiologies: Congenital membranopathies, hemoglobinopathies, enzymopathies, metabolic defects, and immune-mediated destruction. Useful studies include the following:
- a. Reticulocyte count: Usually elevated; indicates increased production of RBCs to compensate for increased destruction. Corrected reticulocyte count (CRC) accounts for differences in HCT and is an indicator of erythropoietic activity. A CRC >1.5 suggests increased RBC production as a result of hemolysis or blood loss
- b. Plasma aspartate aminotransferase and lactate dehydrogenase: Increased from release of intracellular enzymes
- c. Haptoglobin: Binds free Hb; decreased with intravascular and extravascular hemolysis. Also, can be decreased in patients with liver dysfunction secondary to decreased synthesis, as well as in neonates
- d. Direct Coombs test: Tests for the presence of antibody or complement on patient RBCs. Can be falsely negative if affected cells have already been destroyed or antibody titer is low
- e. Indirect Coombs test: Tests for free autoantibody in the patient's serum after RBC antibody binding sites are saturated
- f. Osmotic fragility test: Useful in diagnosis of hereditary spherocytosis. Can also be positive in ABO incompatibility, autoimmune hemolytic anemia, or anytime spherocytes are present
- g. Glucose-6-phosphate dehydrogenase (G6PD) assay: Quantitative test used to diagnose G6PD deficiency, an X-linked disorder affecting 10%–14% of African American males. May be normal immediately after a hemolytic episode because older, more enzyme-deficient cells have been lysed. See Chapter 30 for a list of oxidizing drugs
- h. Heinz body preparation: Detects precipitated Hb within RBCs; present in unstable hemoglobinopathies and enzymopathies during oxidative stress (e.g., G6PD deficiency)
- i. Lactate dehydrogenase (LDH): An enzyme found in RBCs; serum levels significantly elevated in intravascular hemolysis and mildly elevated in extravascular hemolysis
- 3. Red cell aplasia: Variable cell size, low reticulocyte count, variable platelet and white blood cell (WBC) counts. Bone marrow aspiration evaluates RBC precursors in the marrow to look for marrow dysfunction, neoplasm, or specific signs of infection
- a. Acquired aplasias:
- (1) Infectious causes: Include parvovirus in children with rapid RBC turnover (infects RBC precursors), Epstein-Barr virus (EBV), cytomegalovirus (CMV), human herpesvirus type 6, or human immunodeficiency virus (HIV)
- (2) Transient erythroblastopenia of childhood (TEC): Occurs from age 6 months to 4 years, with >80% of cases presenting after age 1 year with a normal or slightly low MCV and low reticulocyte count. Spontaneous recovery usually within 4–8 weeks
- (3) Exposures: Include radiation and various drugs and chemicals
- b. Congenital aplasias: Typically macrocytic anemias
- (1) Fanconi anemia: Autosomal recessive disorder, usually presents before 10 years of age; may present with pancytopenia. Patients may have thumb abnormalities, renal anomalies, microcephaly, or short stature. Chromosomal fragility studies may be diagnostic
- (2) Diamond-Blackfan anemia: Autosomal recessive pure RBC aplasia; presents in the first year of life. Associated with congenital anomalies in one third of cases, including triphalangeal thumb, short stature, and cleft lip
- c. Aplastic anemia: Idiopathic bone marrow failure, usually macrocytic
- 4. Physiologic anemia of infancy (physiologic nadir): Decrease in Hb until oxygen needs are greater than oxygen delivery, usually at Hb of 9–11 mg/dL. Normally occurs between age 8–12 weeks for full-term infants and age 3–6 weeks for preterm infants
- 5. Anemia of chronic inflammation: Usually normocytic with normal to low reticulocyte count. Iron studies reveal low iron, TIBC, and transferrin, and elevated ferritin
FIGURE 14-1 Hemoglobin and mean corpuscular volume (MCV) by age and gender.
(Data from Dallman PR, Siimes MA: Percentile curves for hemoglobin and red cell volume in infancy and childhood. J Pediatr 1979;94:26.)
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