Interindividual Biological Variability of Reticulocytes and Their Maturation Fractions in the Pediatric Population.

OBJECTIVES: Because published data about the variability of reticulocyte counts in children are scarce, the interindividual biological variability of the automated reticulocyte count and its maturation fractions according to age and sex were analyzed. METHODS: A retrospective, observational, analytical study was designed to establish and compare normal values of the automated reticulocyte count and its maturation fractions in different age and sex groups. The sample was drawn from results of CBC counts performed in children aged between 2 months and 18 years using an indirect sampling methodology. RESULTS: A total of 9,362 CBC counts were analyzed. Automated reticulocyte count decreased between 2 months and 3 years of age and slowly increased thereafter, showing higher values in girls up to the age of 9 years, and equalized by sex thereafter. Immature reticulocyte fraction increased until 7 months of age; decreased progressively until 4 years of age; and then showed a discreet but constant rise, with significantly higher values in boys older than 1 year. The low-fluorescence fraction was relatively steady, with significantly higher values in girls aged 8 months and older. CONCLUSIONS: The automated reticulocyte count and its maturation fractions show significant variations related to age and sex in pediatric patients.

Evaluation of the Reticulocyte Production Index in the Pediatric Population.

OBJECTIVES: Since hematologic values vary with age in children, we evaluated the agreement between the "traditional" reticulocyte production index (RPI) and an RPI by age (RPI/A)-adjusted normal values. METHODS: A retrospective, observational, and analytical study was performed on CBCs of children with anemia younger than 18 years. The agreement and clinical repercussions of the RPI values were analyzed with an RPI/A developed with theoretical values for different ages. RESULTS: A total of 5,503 tests were analyzed and no systematic error between the two indices was found; however, there were significant proportional differences at higher values that resulted in lower RPI/A in children younger than 15 days and higher RPI/A in children aged 15 days and older. No agreement was observed at any age. The proportion of arregenerative anemia diagnosed using RPI/A was higher in children younger than 15 days and lower in those 15 days and older. CONCLUSIONS: RPI is not an adequate tool for evaluating the erythropoietic capacity of bone marrow in the pediatric population. The disagreement between the results can be explained by the difference in normal hematologic values between children and adults.