Complete blood count in healthy newborns in the first days of life (a comparative analysis against the 20th-century norms): A retrospective cohort study

Complete blood count is one of the most accessible and common laboratory tests available today. In present-day healthy newborns, complete blood count levels differ from the normative values used in the 1970s, which may require critical analysis, clarification, further research, and revision of the concept of norm. Objectives. To identify changes in the hematologic parameters of healthy newborns born in 2022 as compared to those reported in the 1930s and 1967–1970s. Methods. A retrospective cohort study of neonatal records was conducted at the Neonatal Physiology Unit of the Perinatal Center of the Saint Petersburg State Pediatric Medical University (Ministry of Health of the Russian Federation). Eleven hematologic parameters were analyzed in 378 healthy full-term newborns (born in 2022) in their first three days of life with subsequent comparison of the obtained results with the data of 20th-century domestic publications, as well as with Russian and foreign scientific articles published in the last 15 years. The blood of all children was tested once using a Micros ES 60 automated hematology analyzer (HORIBA ABX S.A.S., France). Mathematical and statistical data processing was performed using Microsoft Office Excel 2021 (Microsoft, U.S.). Results. A comparison of red blood cell and hemoglobin levels reported in newborns in their second and third days of life in 1970 and 2022 revealed statistically significant differences, with lower levels observed at present. Mean platelet counts are also significantly lower than those reported in the 1930 and 1970 studies but are almost the same as those reported by other authors in 2012–2019. The mean white blood cell count is slightly higher as compared to the 20th-century normative values. The dynamics of changes in the mean white blood cell count are similar in all studies presented in the article, revealing a marked decrease by the third day of life as compared to the first and second days; however, 20th century data reveals even lower levels on the third day of life. Noteworthy is the decrease in the relative numbers of lymphocytes and band neutrophils with an increase in segmented neutrophils in this study as compared to the 1930, 1970, and 2012 studies. Conclusion. The current mean values and reference intervals of hematologic parameters in healthy newborn babies differ from those presented in scientific studies and medical articles of the 20th century. This fact requires repeat analysis and establishment of new norms due to the increased sensitivity of analysis, the emergence of new procedures, and higher accuracy of equipment, as well as, potentially, due to changes in the maturity criteria and physical development indicators for newborns in the 21st century.