NORMAL HEMATOLOGIC VALUES
The normal ranges for peripheral blood counts vary significantly with age. Normal neonates show a relative polycythemia with a hematocrit concentration of 45%–65%. The reticulocyte count at birth is relatively high at 2%–8%. Within the first few days of life, erythrocyte production decreases, and the values for hemoglobin and hematocrit fall to a nadir at about 6–8 weeks. During this period, known as physiologic anemia of infancy, normal infants have hemoglobin values as low as 10 g/dL and hematocrits as low as 30%. Thereafter, the normal values for hemoglobin and hematocrit gradually increase until adult values are reached after puberty. Premature infants can reach a nadir hemoglobin level of 7–8 g/dL at 8–10 weeks. Anemia is defined as a hemoglobin concentration two standard deviations below the mean for a normal population of the same gender and age.
Newborns have larger red cells than children and adults, with a mean corpuscular volume (MCV) at birth of more than 94 fL. The MCV subsequently falls to a nadir of 70–84 fL at about age 6 months. Thereafter, the normal MCV increases gradually until it reaches adult values after puberty.
The normal number of white blood cells (WBCs) is higher in infancy and early childhood than later in life. Neutrophils predominate in the differential white count at birth and in the older child. Lymphocytes predominate (up to 80%) between about ages 1 month and 6 years.
Normal values for the platelet count are 150,000–400,000/μL and vary little with age.
Failure of the marrow to produce adequate numbers of circulating blood cells may be congenital or acquired and may cause pancytopenia (aplastic anemia) or involve only one cell line (single cytopenia). Constitutional and acquired aplastic anemias are discussed in this section and the more common single cytopenias in later sections. Bone marrow failure caused by malignancy or other infiltrative disease is discussed in Chapter 31. It is important to remember that many drugs and toxins may affect the marrow and cause single or multiple cytopenias.
Suspicion of bone marrow failure is warranted in children with pancytopenia and in children with single cytopenias who lack evidence of peripheral red cell, white cell, or platelet destruction. Macrocytosis often accompanies bone marrow failure. Many of the constitutional bone marrow disorders are associated with a variety of congenital anomalies.
CONSTITUTIONAL APLASTIC ANEMIA (FANCONI ANEMIA)
ESSENTIALS OF DIAGNOSIS & TYPICAL FEATURES
Multiple congenital anomalies.
Increased chromosome breakage in peripheral blood lymphocytes.
Fanconi anemia, which is the most common inherited bone marrow failure syndrome, is characterized by defective DNA repair that is caused by a variety of genetic mutations. Inheritance is autosomal recessive, and this disease occurs in all ethnic groups; 75%–90% of affected individuals develop bone marrow ...