Flow-cytometric analysis of reticulocytes in normal cord blood.

We performed precise reticulocyte counts and a reticulocyte maturation study according to ribosomal RNA (rRNA) content, in normal cord blood. For this purpose we analyzed 35 cord blood specimens corresponding to a mean gestational age of 39.2 weeks (range 38-41). In all specimens complete blood counts were performed with the H*1 (Technicon, Bayer) analyzer. Reticulocyte maturation study and counts were conducted by the R-1000 (Sysmex) reticulocyte analyzer. We obtained the following measurements (mean +/- 1 SD): reticulocyte percentage 3.11 +/- 0.75% and reticulocyte absolute count 137.3 +/- 33.3 x 10(9)/l. There was no correlation between the reticulocyte counts and the duration of gestation or the type of labor (normal, forceps assisted or cesarean section). Reticulocyte subpopulations with different rRNA content and maturation were expressed as reticulocytes with high (HFR), median (MFR) and low (LFR) fluorescence of the fluorochrome auramine bound to rRNA. Normal cord values were: HFR% = 13.6 +/- 2.4, MFR% = 22.5 +/- 2.4 and LFR% = 63.9 +/- 4.3. Reference maturation subpopulations were assessed for comparison in 180 samples of healthy adults (90 males and 90 females) and were found HFR% = 1.0 +/- 0.8, MFR% = 9.7 +/- 3.3 and LFR% = 89.2 +/- 3.4. The HFR% and MFR% were significantly higher while LFR% was significantly lower (p < 0.001) in cord compared to adult blood, denoting a shift to more immature reticulocyte forms. The above values are provided as normal reference data of the reticulocyte maturation profile in full-term cord blood.