Abstract
Young infants do not have a consolidated circadian system, although ultradian and circadian components have been shown in body temperature, heart rate, and blood pressure. The goal of our study was to determine whether blood counts in young infants exhibit rhythmicity. Blood samples were taken from 55 healthy infants 1–8 weeks of age, seen at the emergency room of the Afula Medical Center, Israel. The data were sorted by clock hour of patient assessment before analysis by the cosinor method for periodicities. Ultradian, rather than circadian, compound rhythms were observed in hemoglobin levels, neutrophile and platelet counts. In conclusion, a trend of compound ultradian time pattern was demonstrated in young infants' blood counts.