Relationship between maturity and isoenzymes of erythrocytic carbonic anhydrase in newborn infants.

The present study was carried out to assess the activities of all three principal isoenzymes of human erythrocytic carbonic anhydrase (HCA) in newborn infants in relation to their estimated gestational ages. Blood samples were collected at parturition from the umbilical cords of 45 normal healthy infants. Among the samples taken before day 290 of gestation, the activity ratio (isoenzyme B: isoenzyme C) was correlated significantly with estimated gestational age. After day 290, the range of B:C activity ratios was similar to that observed in adults. Isoenzyme A represented a relatively constant proportion (mean +/- SEM) at 7.2 +/- 0.2% of total HCA activity. The B:C activity ratio appears to be a more reliable and sensitive index of maturity than either the total HCA activity or the ratio of total HCA activity to the total hemoglobin concentration in cord blood.