RT Book, Section A1 Ambruso, Daniel R. A1 Nuss, Rachelle A1 Wang, Michael A2 Hay, Jr., William W. A2 Levin, Myron J. A2 Deterding, Robin R. A2 Abzug, Mark J. SR Print(0) ID 1153313268 T1 Hematologic Disorders T2 Current Diagnosis & Treatment: Pediatrics, 24e YR 2018 FD 2018 PB McGraw-Hill Education PP New York, NY SN 9781259862908 LK accessmedicine.mhmedical.com/content.aspx?aid=1153313268 RD 2022/05/20 AB The normal ranges for peripheral blood counts vary significantly with age. Normal neonates have a hematocrit 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.