TY - CHAP M1 - Book, Section TI - Hematologic Disorders A1 - McKinney, Christopher A1 - Nuss, Rachelle A1 - Wang, Michael A2 - Bunik, Maya A2 - Levin, Myron J. A2 - Abzug, Mark J. A2 - Schreiner, Teri L. Y1 - 2025 N1 - T2 - Current Diagnosis & Treatment: Pediatrics, 27th Edition AB - The normal ranges for peripheral blood counts vary with age. Neonates have a hematocrit of 45%–65% accompanied by an increased reticulocyte count of 2%–8% in the first 24 hours. Within the first few days of life, erythrocyte production decreases as serum erythropoietin levels fall in response to increased tissue oxygenation, and the hemoglobin and hematocrit fall to a physiologic nadir around 10 g/dL and 30%, respectively, at 6–8 weeks of life. Thereafter, the normal values for hemoglobin and hematocrit gradually increase until adult values are reached after puberty with post-pubertal males having an average hemoglobin concentration about 1 g/dL higher than postpubertal females. Premature infants may have a more exaggerated and delayed hemoglobin nadir of 7–8 g/dL at 8–10 weeks. Anemia is defined as a hemoglobin concentration less than the 2.5th percentile for a normal population of the same gender and age. SN - PB - McGraw Hill CY - New York, NY Y2 - 2025/03/21 UR - accessmedicine.mhmedical.com/content.aspx?aid=1211984374 ER -