Amniostat-FLM: an initial clinical trial with both vaginal pool and amniocentesis samples

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.

Maturity testing with preterm premature rupture of the membranes

The presence or absence of fetal pulmonary maturity as assessed by amniotic fluid analysis and the role of fetal maturity tests in the management of premature rupture of the membranes are addressed. The hazards of the high falsely immature test are carefully explored. A management scheme based on the results of amniotic fluid analysis is also described.

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.

Use of Amniostat-FLM in detecting the presence of phosphatidylglycerol in vaginal pool samples in preterm premature rupture of membranes

OBJECTIVE

The presence of phosphatidylglycerol in amniotic fluid from the vaginal pool has been established as a reliable marker of pulmonary maturity in pregnancies complicated by preterm premature rupture of membranes because its presence is not affected by contaminants. This study was undertaken to determine the distribution of positive phosphatidylglycerol relative to gestational age from vaginal pool amniotic fluid samples and to assess the efficacy and accuracy of the Amniostat-FLM (Hana Biologics; Irvine Scientific after Sept. 14, 1989), an antibody agglutination method for rapidly detecting phosphatidylglycerol.

STUDY DESIGN

All singleton nondiabetic pregnancies between 26 and 36 weeks with premature rupture of membranes from whom a vaginal pool sample was obtained were studied. The percent positive by gestational age was analyzed. The neonates that were delivered with a positive phosphatidylglycerol were evaluated for the presence of hyaline membrane disease and other immediate sequelae of prematurity.

RESULTS

Of the 201 vaginal pool amniotic fluid samples assayed for phosphatidylglycerol with the Amniostat-FLM procedure, 18% (36/201) were positive for phosphatidylglycerol and none of the delivered infants developed hyaline membrane disease.

CONCLUSION

The Amniostat-FLM seems to be accurate in predicting pulmonary maturity from vaginal pool samples.

Prediction of RDS by amniotic fluid analysis: a comparison of the prognostic value of traditional and recent methods

The determination of lecithin or even more the lecithin/sphingomyelin (L/S) ratio in amniotic fluid are both well established in the prediction of neonatal RDS. The immunological measurement of phosphatidylglycerol (PG) and the determination of the surfactant/albumin (S/A) ratio by fluorescence polarization (TDx FLMR) have recently been introduced for the detection of fetal lung maturity. In order to compare traditional versus recent methods L/S ratio and PG determination by one dimensional thin-layer chromatography, enzymatic analysis of lecithin, immunological determination of PG by Amniostat-FLMR and the fluorescence polarization of S/A-ratio by the TDx FLMR were all performed in 141 amniotic fluid samples of 122 patients. Only one out of 72 samples was false negative in the enzymatic lecithin determination (sensitivity 88%). All other methods have a sensitivity and a negative predictive value of 100%. The positive predictive values and the specificity varied between 22%-50% and 58%-87% respectively. The false positive rate, which is high for all methods, is lowest for the L/S ratio. This study demonstrates, that the recent methods are reasonable alternatives in all cases with a positive test. In clinical practice they have the advantage, that the result can be obtained in 15 minutes. If the test is predictive for lung immaturity the L/S ratio should be performed in addition to decrease the false positive rate before any clinical decision is made.

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.

Evaluation of the new amniostat-FLM test for the detection of phosphatidylglycerol in contaminated fluids

The Amniostat-FLM rapid slide test (Hana Biologics, Inc., Alameda, Calif.) for detection of phosphatidylglycerol has previously been evaluated and has shown good correlation with the more sophisticated two-dimensional thin-layer chromatographic method. A new, ultrasensitive kit has now been released with a lower level of detection of 0.5 microgram of phosphatidylglycerol per milliliter of fluid. This is the first report of this new kit, which we used with vaginal pool samples and with contaminated amniocentesis samples. We evaluated this kit for concordance with thin-layer chromatography results as well as fetal outcome. Of 48 vaginal pool samples, 41 (85%) showed concordance, whereas 39 of 42 (93%) contaminated amniocentesis samples were concordant, for an overall concordance of 89% (80 of 90 samples). Sixty-seven infants were delivered within 72 hours of the test and there were no cases of hyaline membrane disease in the presence of a positive test result. We conclude that this new, ultrasensitive kit is a good, time-saving, and reliable test for the detection of phosphatidylglycerol without the development of false-positive results even when tested on the worst possible fluid samples. A review of clinical studies involving the Amniostat-FLM is also presented.

Current perspectives in assessment of fetal pulmonary surfactant status with amniotic fluid

In recent years, improvements in analytical methodology and clinical management of maternal-fetal diseases have altered the understanding of data from amniotic fluid analysis. Delays in phospholipid production or lung function are not currently reported in maternal diabetes. Fetal lung function following glucocorticoid therapy or premature membrane rupture is uncoupled from amniotic fluid phospholipid concentrations, which do not have the usual significance in these circumstances. Phosphatidylglycerol (PG) is present prior to the usual time it is detected by thin layer chromatography (TLC) methods, which vary in sensitivity for PG. Consequently, the significance of its "absence" is highly varied. These observations are discussed in light of the earlier methods and data, along with new perceptions of the functions of the individual phospholipids and apoproteins, the regulatory mechanism of surfactant production, and the relationship of amniotic fluid components to neonatal lung function.

Production of a phosphatidylglycerol-like substance by genital flora bacteria

Bacteria contaminating amniotic fluid have anecdotally been shown to produce a phosphatidylglycerol-like substance, thus giving false positive tests for phosphatidylglycerol in vaginal pool fluid from patients with premature rupture of the membranes. Isolates of Escherichia coli, Proteus mirabilis, Acinetobacter calcoaceticus, Klebsiella pneumoniae, Staphylococcus aureus, coagulase-negative Staphylococcus, Streptococcus faecalis, and Streptococcus agalactiae (group B streptococcus) were grown in broth and analyzed for the presence of phosphatidylglycerol-like material by one-dimensional thin-layer chromatography and also by a polyclonal, immunologic slide agglutination test (Amniostat-FLM). All species demonstrated a positive test result for phosphatidylglycerol by either thin-layer chromatography, slide agglutination, or both. The material migrated separately from cardiolipin and phosphatidylethanolamine as determined by chromatography, but identically with the phosphatidylglycerol control. Gram-negative species were more strongly positive than gram-positive organisms. Colony counts on the order of 10(8) colony-forming units per milliliter were necessary to give positive test results for phosphatidylglycerol. The possible clinical implications of these findings are discussed.