Chapter 14: Hematology
- A. General Evaluation
Anemia is defined as a reduction in hemoglobin (Hb) two standard deviations below the mean, based on age-specific norms ( Table 14-1 and Fig. 14-1). Evaluation should include:
- 1. Complete history, including nutrition, menstruation, ethnicity, fatigue, pica, medication exposure, growth and development, blood loss, hyperbilirubinemia and family history of anemia, splenectomy, or cholecystectomy.
- 2. Physical examination, including evaluation of pallor, tachycardia, cardiac murmur, jaundice, hepatosplenomegaly, glossitis, tachypnea, koilonychia, angular cheilitis or signs of systemic illness.
- 3. Initial laboratory tests including complete blood cell count (CBC) with red blood cell (RBC) indices (mean corpuscular volume [MCV], mean corpuscular hemoglobin [MCH], red cell distribution width [RDW]), reticulocyte count, stool for occult blood, urinalysis, and serum bilirubin. Complete evaluation always includes a peripheral blood smear.
- B. Diagnosis
Anemias may be categorized as macrocytic, microcytic, or normocytic. Table 14-2 gives an approach to diagnosis based on RBC production as measured by reticulocyte count and cell size. Note that normal ranges for Hb and 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 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, elevated total iron-binding capacity (TIBC), low mean corpuscular 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 after 3 months of therapy.
- d. Mentzer index (MCV/RBC): Index >13.5 suggests iron deficiency; expect elevated RDW. Mentzer index <11.5 suggests thalassemia minor; expect low/normal RDW.
- 2. Hemolytic anemia: Rapid RBC turnover. Etiologies: Congenital membranopathies, hemoglobinopathies, enzymopathies, metabolic defects, and immune-mediated destruction. Useful studies include:
- 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. CRC >1.5 suggests increased RBC production secondary to hemolysis or blood loss.
- b. Plasma aspartate aminotransferase (AST) and lactate dehydrogenase (LDH): Increased from release of intracellular enzymes. Serum LDH levels are significantly elevated in intravascular hemolysis and mildly elevated in extravascular hemolysis.
- c. Haptoglobin: Binds free Hb; decreased with intravascular and extravascular hemolysis. Can also be decreased in patients with liver dysfunction secondary to decreased hepatic synthesis and in neonates.
- d. Direct Coombs test: Tests for presence of antibody or complement on patient RBCs. May be falsely negative if affected cells have already been destroyed or antibody titer is low.
- e. Indirect Coombs test: Tests for free autoantibody in patient’s serum after RBC antibody binding sites are saturated. Positive indirect test with negative direct test is typical of alloimmune sensitization (e.g., transfusion reaction).
- 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 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. For a comprehensive list of oxidizing drugs, go to:http://g6pddeficiency.org/index.php?cmd=contraindicated.
- h. Heinz body preparation: detects precipitated Hb within RBCs; present in unstable hemoglobinopathies and enzymopathies during oxidative stress (e.g., G6PD deficiency).
- 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: 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 occurs 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 can be diagnostic.
- (2) Diamond-Blackfan anemia: Autosomal recessive pure RBC aplasia; presents in the first year of life. Associated with congenital anomalies in 30%-47%12 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 exceed oxygen delivery, usually at Hb of 9–11mg/dL. Normally occurs at 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.)
Chapter 14: Hematology was found in Harriet Lane Handbook.
If you are a registered user, please log in below.
If not, learn more about gaining full access.
- Harriet Lane Handbook is the authoritative source of practical pediatric information for interns, residents, and pediatricians.
Try these free topics now!