States of stability/lysis in human fetal and adults red blood cells

Cord blood red cell osmotic fragility: a comparison between preterm and full-term newborn infants

BACKGROUND

The osmotic fragility of red blood cells reflects their membrane ability to maintain structural integrity. The osmolality at which the cells lyse is related to their shape, deformability, surface area/volume ratio and intrinsic membrane properties. In cord blood, there may be differences between premature and term infants, and be influenced by maternal medication and other factors. There have been no definitive findings on possible differences between preterm and full-term infant osmotic fragility.

AIMS

To determine if cord blood erythrocyte osmotic fragility differs between premature and full-term newborn infants, using two parallel techniques.

PATIENTS AND METHODS

Cord blood samples were obtained from preterm singletons (N=11), preterm multiple births (N=10), full-term infants (N=24), as well as adults (N=22), for comparison. An osmotic fragility test was used to determine the NaCl concentration at which 20%, 50% and 80% of hemolysis occurred using individual logistic curves. A glycerol lysis test determined the time needed to lyse 50% of red blood cells.

RESULTS

Cord blood red cells of multiple birth premature infants were more hemolysis-resistant than erythrocytes from full-term infants or adults. Another index of osmotic fragility, the difference in NaCl concentration for 80% and 20% red cell hemolysis showed that premature infants had greater differences than full-term infants or adults. Glycerol lysis time revealed that both preterm and full-term infants had an erythrocyte subpopulation that took longer than adult blood to attain 50% hemolysis. Correlation between both tests was very significant (r=-0.603, P<0.0001, N=67).

CONCLUSIONS

This study shows that erythrocytes of premature infants, although, in average, less osmotically fragile than those of healthy full-term infants, contain a more hemolysis-susceptible cell subpopulation.

Improved automated leucocyte counting and differential in newborns achieved by the haematology analyser CELL-DYN 3500

Automated leucocyte counts in newborns generated by the impedance principle are artificially affected by the high osmotic resistance of some newborn RBC and possibly by the high normoblast numbers present during the neonatal period. Erroneously high WBC counts may result. The haematology analyser CELL-DYN 3500 (Abbott Diagnostika GmbH, Wiesbaden-Delkenheim, Germany) has two different channels for the WBC count, an electrical resistivity (impedance) channel and a laseroptical channel. In combination with facultative extended lysis of resistant RBC before WBC count, this instrument is claimed to be very suitable for newborn blood analysis. We measured the WBC count and differential of 165 blood samples from newborns and cord blood on the CELL-DYN 3500. Reticulocyte count and manual differential including normoblasts were determined. Furthermore, some technical aspects of neonatal blood analysis were evaluated: precision, cell stability, effect of incorrect blood-anticoagulant ratio of small blood collecting tubes. The internal decision making process of the CELL-DYN 3500 selects the result either from the optical channel (identifies and excludes normoblasts) or from the resistivity channel (eliminates resistant RBC). This instrument gives a reliable and accurate WBC count and differential of neonatal samples even in blood samples with normoblasts and lytic resistant RBC. The result given by the CELL-DYN 3500 can be confirmed by a subsequent run in extended lyse mode.