The relationship of lactic dehydrogenase to epithelial cells in the urine of normal neonates.

Urinary lactic dehydrogenase (LDH) isoenzyme assays in 20 female and 15 male normal newborn infants during the first 3 days of life revealed higher levels than in older populations and a tendency toward a "slow zone pattern" (predominance of isoenzymes 4 and 5). Total LDH and LDH-5 activities were higher in the female (33.2 +/- 5.2 and 12.4 +/- 2.8 mU/mL, respectively), than in the male population (9.7 +/- 2.2 and 1.0 +/- 0.3 mU/mL, respectively). The amount of LDH correlated with the presence of epithelial cells in the urine that also were prominent in female patients and were apparently derived from the vagina. Separation of epithelial cells by centrifugation and filtration decreased total LDH and isoenzyme activities in the remaining sample, while sonification of the resuspended cells increased TLDH and LDH-5 activities by 6- and 12-fold respectively. Saline washings of the perineum and vagina revealed large numbers of epithelial cells and similar LDH isoenzyme patterns suggesting that contamination of the urine with these cells is a frequent occurrence during collection of voided and/or bag urine samples, and that these cells are responsible for much of the LDH activity found in the urine. We conclude that epithelial cells can increase both total LDH and isoenzyme activity in voided urine samples from otherwise normal female neonates. In this age group, urine collected by other methods (catheterization or suprapubic aspiration) must be studied to minimize the possibility of contamination of the sample with epithelial cells from the vagina or the perineum or both.