Assessment of the AmnioStat-FLM immunoagglutination test for phosphatidylglycerol in amniotic fluid

Techniques to evaluate surfactant activity for a personalized therapy of RDS neonates

According to both European and American Guidelines, preterm neonates have to be treated by nasal continuous air pressure (CPAP) early in the delivery room. The administration of surfactant should be reserved only for babies with respiratory distress syndrome (RDS) with increased oxygen requirement, according to different thresholds of FiO₂. However, these oxygenation thresholds do not fully take into consideration the lung physiopathology and mechanics or the lung surfactant biology of RDS neonates. Since surfactant replacement therapy (SRT) seems to be more effective if it is initiated within the first 3 hours after birth, the use of a reliable bench-to-bedside biological test able to predict as soon as possible the necessity of SRT will help optimise individualised therapies and personalise the actual collective strategy used to treat RDS neonates. With this in mind, in the present review several quantitative and qualitative biological tests to assess the surfactant status in RDS neonates are introduced as potential candidates for the early prediction of SRT requirement, summarising the state-of-the-art in the evaluation of surfactant activity.

Strategic utilization of fetal lung maturity tests

We have retrospectively investigated the diagnostic efficiency of the Abbott TDxFLM (fetal lung maturity) assay as compared to the lecithin/sphingomyelin ratio (LSR) and phosphatidylglycerol (PG) or PG/sphingomyelin (PG/S) ratio. Our results are consistent with other published studies. A review of the literature revealed that 1759 patients have been studied, and 213 neonates were found to have respiratory distress syndrome (RDS). This included samples from different sources and patients with various pathological conditions including diabetes. The TDxFLM assay has the highest sensitivity, followed by PG and LSR. The specificity of LSR is only slightly better than TDxFLM, whereas PG is the least specific. While the LSR assay y thin layer chromatography is affected by blood and meconium, the PG test by AmnioStat-FLM is not. A study on the effect of serum, whole blood and meconium on the TDxFLM assay revealed that blood elevated its value, but serum and meconium depressed the result. A sample contaminated with meconium may be tested and the result interpreted with the same degree of confidence if maturity is indicated. However, bloody specimens require a confirmatory test, such as PG measurement with the AmnioStat-FLM assay. On consideration of the diagnostic efficiency of the FLM tests, we propose a sequential testing strategy to optimize the use of the laboratory and clinical care. The use of the TDxFLM assay is suggested as the initial test. If the sample is contaminated with blood, or when the result falls within the indeterminate region, the AmnioStat-FLM will be used as a second test. This strategic utilization of FLM tests will provide cost effective high quality patient care.

Clinical evaluation of a direct colorimetic method for determination of amniotic phospholipids

Evaluation of amniotic phospholipids, which are a parameter of fetal lung maturation, is important in the management of premature infants. The method available for measuring the lecithin/sphingomyelin (L/S) ratio, which appears to provide an index to fetal lung maturity, is laborious, involving determinations of phospholipids, and so is unsuitable for rapid quantitative measurement of phospholipids in the amniotic fluid in the perinatal period. We developed a simple, sensitive colorimetric assay for phospholipids without their extraction. This assay is based on the fact that phospholipids form stable hydrophobic complexes with Co(SCN)4, Fe(SCN)2- and Fe(SCN)3 within about 1 hr. Amniotic fluid samples (n = 115) were collected from women with normal and abnormal pregnancies in week 16-41 of pregnancy, and these samples were examined both by thin layer chromatography (TLC) and by our method of phospholipid determination. Good correlations were observed between the L/S ratio determined by TLC and the values obtained by this method. Moreover the distributions of the dipalmitoylphosphatidylcholine (DPPC) content and DPPC/sphingomyelin (SM) ratio were similar to those of the PC content and L/S ratio. This method was proved to be more accurate than other methods such as TLC and the shake test for predicting neonatal RDS.

Combined enzymatic assay of phosphatidylglycerol and phosphatidylcholine in amniotic fluid

We present here a combined, quantitative enzymatic procedure for determining amniotic fluid phosphatidylglycerol and phosphatidylcholine and relate these findings to the assessment of fetal lung maturity. Under the assay conditions described phospholipase C specifically hydrolyses phosphatidylglycerol (PG) and phosphatidylcholine (PC) but not sphingomyelin, precluding the need for removal of sphingomyelin prior to analysis. Solvent extraction of the phospholipids from the amniotic fluid is, however, employed to avoid spurious elevation of PG and PC results by endogenous glycerol and choline. Of 45 amniocentesis fluids examined, 28 yielded detectable PG concentrations (greater than 0.5 mumol/l) and all but three of these exhibited PC concentrations in excess of 10 mumol/l. One case of respiratory distress occurred in an infant of 29 wk gestation with severe intrauterine growth retardation. Of the remaining 17 fluids in which PG was undetected enzymatically (less than or equal to 0.5 mumol/l), 14 also contained PC concentrations less than or equal to 10 mumol/l and all six cases of true respiratory distress syndrome came from within this sub-group. Strong correlations between the PC concentration and the lecithin:sphingomyelin ratio, r = 0.85 (p less than 0.001) and the PC and PG concentrations, r = 0.96 (p less than 0.001) were also found.