SUMMARY.A longitudinal investigation of changes in red blood cell (RBC) size distribution and zinc protoporphyrin/haemoglobin (ZPP/Hb) ratio was performed.In the course of the first few weeks after birth RBC size distribution histograms show a loss of macrocytic RBCs demonstrated by a rapid decrease of the fraction of macrocytes, whereas the degree of RBC volume dispersion decreases simultaneously. Within this period a significant change in the fraction ofmicrocytes was not observed. At about 6 months of age, a marked shift of RBC size distribution histograms towards lower volumes occurs. Concomitant with the lower MCV values, the values for the absolute distribution width at half peak height (ADW o .j ) also showed an obvious decrease.At birth, ZPP/Hb ratios are about three times higher than those of adult subjects and decrease slowly during infancy. This suggests that iron deficiency is unlikely in the first months of life.
Additional key phrases: erythron; red cell size distribution histogram; fraction of microcytes; fraction of macrocytesInformation on alterations in the erythron and the effect of changes in iron status may be derived from red blood cell (RBC) size distribution histograms' and the ZPP/Hb ratio.i" Because of the small size of blood samples available from neonates, the number and type of additional biochemical determinations is limited.Modem haematology analysers can provide quantitative measures derived from RBC size distribution histograms from a few drops of blood. Reports from several investigators?" show that studies of RBC size dispersion are useful in screening subjects for haematological abnormalities and may supply additional diagnostic information.?'!?Few investigations have been published on the evaluation of qualitative and quantitative features of RBC size distribution histograms of neonates."" The objective of this study was to determine how RBC size distribution histograms and other haemocytometric values vary in time within the neonatal period. Therefore, values established for the ADW o . j , the fraction of microcytes and the fraction of macrocytes are Correspondence: Dr P C Bartels.