Phosphatidylglycerol in amniotic fluid. Comparison of an "ultrasensitive" immunologic assay with TLC and enzymatic assay.

Phosphatidylglycerol (PG) in amniotic fluid is recognized as a good indicator of fetal lung maturity and is unaffected by moderate amounts of blood or meconium contamination. A rapid immunologic agglutination assay, Ultrasensitive AmnioStat-FLM (FLM), was compared with two-dimensional thin-layer chromatography (TLC) and an enzymic, colorimetric procedure (E-PG). Eighty amniotic fluid specimens were analyzed. FLM results were reported as high (H), intermediate (I), or low positive (L). TLC was compared with FLM:H (n = 27), mean 0.14 (fraction of total phospholipids); I (n = 7), mean 0.11; L (n = 9), mean 0.03; negative results had no detectable PG by TLC. In 33 cases E-PG was compared with FLM:H (n = 9), mean 7.0 mumol/L; I (n = 5), mean 8.1 mumol/L; L (n = 3), mean 3.0 mumol/L; negative (n = 16), mean 3.2 mumol/L. Records were reviewed in 70 cases. Thirty cases were excluded: sample to delivery time was greater than 72 hours; steroids were given or sepsis was documented. Fetal lung immaturity was clinically present in six cases: respiratory distress syndrome in three cases and transient tachypnea of the newborn (TTN) in three cases. One false positive result was identified (TTN, FLM:H). FLM sensitivity for fetal lung maturity was 85.3%, specificity was 83.3%, and the positive predictive value for fetal lung maturity was 96.7%. FLM is a fast, reliable indicator of fetal lung maturity.

Bilirubin interference in a peroxidase-coupled procedure for creatinine eliminated by bilirubin oxidase.

A colorimetric peroxidase-coupled procedure for determination of creatinine in human serum and urine is described. A 30-s sample pre-treatment with bilirubin oxidase eliminates interference from endogenous bilirubin. The 4-aminoantipyrine-2-hydroxy-3,5-dichlorobenzenesulfonate chromogen system of this method is about fourfold more sensitive than current procedures that involve monitoring NAD(P)H and nearly fivefold more sensitive than the traditional picrate procedures. Incorporation of a sample blank eliminates positive interference from endogenous creatine. Results of the proposed procedure are somewhat lower than those of the common kinetic or equilibrium picrate techniques, as would be expected because of the effects of the well-known interferences in the latter methods.