Measurement of red cell enzymes in newborn infants.

Red cell enzyme activity was m easured in packed red cells obtained from spun hematocrit tubes and compared with results obtained using standard methods (washed, filtered, red blood cells [WFRBC]) in order to evaluate the feasibility of using heel puncture as a means of obtaining accurate quantitative red cell enzym e data in the new born period. Glucose-6phosphate dehydrogenase (G-6-PD) and pyruvate kinase (PK) were studied in 10 adults, and G-6-PD, PK, phosphofructokinase (PFK), and phosphoglycerate kinase (PGK) in 10 cord bloods. After centrifugation of the hematocrit tubes, the plasma and buffy coat and clay w ere rem oved by filing, and red cells for enzyme assay were sampled from either the top (or “plasm a-end”) or the bottom (or “clayend”) of the packed red blood cells rem aining in the microhematocrit tube. The activities of PK and G-6-PD were significantly higher in the upper or “plasma-end” (P) of red cells sam pled from spun hem atocrit tubes in adults and cord blood. Red cell PFK activity was also higher in P than in the bottom or “clay-end” (C) in cord blood; PGK was similar in P and C. Thus, the site of sampling from hem atocrit tubes affects results, not only for the age-dependent enzym es, bu t in cord blood for certain non-age-dependent enzymes such as PFK, as well. Red cell PK activity was significantly different in spun hem atocrit tubes and WFRBC in adults and cord blood, with the exception of PK activity in P and WFRBC in adults w hich w ere not significantly different. However, G-6-PD, PFK and PGK activities w ere not statistically different in red cells obtained from the “clay-end” of hem atocrit tubes and WFRBC. There was no evidence of w hite cell contam ination affecting total red cell enzyme activity. Thus, it appears from these studies that red cell G-6-PD and most glycolytic enzymes can be accurately m easured in newborns by sampling from the “clay-end” or bottom portion of the packed red cells in spun hematocrit tubes obtained via heel puncture.