Performance of the amniotic fluid foam stability—50 percent test

Abstract We have evaluated refractive index-matched anomalous defraction (RIMAD) (Dubin SB, Clin Chem 1988;34:938-43) as a potential method for assessment of fetal lung maturity (FLM). This method determines the total light scattered by the surfactant-containing lamellar bodies by subtraction of the A650 from amniotic fluid diluted in glycerol from that of amniotic fluid diluted in distilled water. It is not significantly affected by such contaminating chromogens as hemoglobin and bilirubin up to 2.0 g/L and 11.0 mg/L, respectively. However, the addition of as little as 2.5 microL of erythrocytes as whole blood resulted in significant interference. RIMADs for normal respiratory outcomes (n = 78) ranged from 0.018 to 0.471. RIMADs for respiratory distress syndrome (RDS) outcomes (n = 8) ranged from 0.004 to 0.036. Use of a RIMAD referent value of > 0.040 to indicate maturity yielded sensitivity, specificity, predictive value (PV)RDS, and PVmaturity of 100%, 96.2%, 72.2%, and 100%, respectively. The areas under the receiver-operating characteristic curves were 0.997 for the RIMAD assay, 0.993 (P = 0.3) for the TDx-FLM assay, 0.89 (P = 0.017) for the lecithin/sphingomyelin ratio, and 0.87 (P = 0.023) for the foam stability index.

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Evaluation of two assays of functional surfactant in amniotic fluid: surface-tension lowering ability and the foam stability index test.

Clinical Chemistry ◽

10.1093/clinchem/25.10.1770 ◽

1979 ◽

Vol 25 (10) ◽

pp. 1770-1773 ◽

Cited By ~ 4

Author(s):

B E Statland ◽

D E Freer

Keyword(s):

Surface Tension ◽

Amniotic Fluid ◽

Volume Fraction ◽

Foam Stability ◽

Stability Index ◽

Hyperbolic Function ◽

Index Test ◽

Foam Formation ◽

Stable Foam ◽

Practical Standpoint

Abstract We characterize two assays of total amniotic fluid surfactant that are based on function: the surface-tension lowering ability of extracts of amniotic fluid lipid (I) and the foam stability index test (II). I is determined on chloroform extracts of amniotic fluid. II is defined as the highest ethanol volume fraction of an amniotic fluid-ethanol mixture that will permit a stable foam to form after 30 s of vigorous shaking. The relationship of I to disaturated phosphatidylcholine concentrations (after osmium tetroxide treatment of the amniotic fluid lipid extract) is in the expected theoretical form of a hyperbolic function. The relation between values for II and disaturated phosphatidylcholine concentrations showed a consistent bias, suggesting that components other than disaturated phosphatidylcholine contribute to stable foam formation. Phosphatidylclycerol concentrations did not appear to account for this bias. The relation between I to II values suggest that both assays measure total surfactant. I, II, and concentration of disaturated phosphatidyl choline are all excellent indicators of fetal pulmonary maturity. From a practical standpoint, the foam stability index test is the most efficient approach to routine assessment of fetal pulmonary status.

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Measurement of amniotic fluid surfactant.

Clinical Chemistry ◽

10.1093/clinchem/27.10.1629 ◽

1981 ◽

Vol 27 (10) ◽

pp. 1629-1641 ◽

Cited By ~ 21

Author(s):

D E Freer ◽

B E Statland

Keyword(s):

Surface Tension ◽

Clinical Outcome ◽

Amniotic Fluid ◽

Foam Stability ◽

Amniotic Fluid Volume ◽

Fetal Maturity ◽

Sources Of Variation ◽

Surfactant Phospholipids ◽

And Storage

Abstract Measurement of the production of surfactant is the most direct means of prenatally assessing fetal pulmonary maturity. We review assays which have evolved for measuring surfactant, classifying them into two general categories: biochemical quantitation and biophysical measurements. Biochemical quantitation assays include the amniotic fluid lecithin/sphingomyelin ratio and quantitation of lecithin and other surfactant phospholipids. Biophysical measurements include measurement of surface-tension-lowering ability of extracts of amniotic fluid lipid and evaluation of surface-tension-related properties such as foam stability and microviscosity. Assays of surfactant are subject to certain pre-analysis sources of variation over which the analyst has no control, such as variability in total in vivo amniotic fluid volume, incomplete in vivo mixing of surfactant with amniotic fluid, and presence of contaminating blood or meconium. We also examine other factors such as centrifugation speed and time, and storage of the amniotic specimen before analysis. These factors can dramatically affect analyses, and must be carefully controlled by the analyst. In general, both biochemical and biophysical approaches to surfactant analysis are useful diagnostically. When properly performed, both approaches give results that correlate well, both with each other and with clinical outcome. Because "mature" and "immature" values overlap, none of the assays can completely eliminate false predictions, whether of fetal maturity or fetal immaturity.

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Rational basis for foam-stability assays of amniotic fluid surfactant.

Clinical Chemistry ◽

10.1093/clinchem/24.11.1980 ◽

1978 ◽

Vol 24 (11) ◽

pp. 1980-1984 ◽

Cited By ~ 1

Author(s):

D E Freer ◽

B E Statland ◽

G Sher

Keyword(s):

Amniotic Fluid ◽

Volume Fraction ◽

Foam Stability ◽

Chemical Species ◽

Bovine Brain ◽

Rational Basis ◽

Artificial System ◽

Stable Foam ◽

Dimyristoyl Phosphatidylcholine ◽

The Relationship

Abstract We evaluated the relative contributions of various phospholipids to the formation of foam in the amniotic fluid "foam stability test", by use of an artificial system of saline, ethanol, and dipalmitoyl 3-sn-phosphatidylcholine to determine the relationship between dipalmitoyl 3-sn-phosphatidylcholine concentration, ethanol volume fraction, and the threshold of formation of stable foam. At dipalmitoyl 3-sn-phosphatidylcholine concentrations of 20, 40, and 80 mg/liter, the threshold ethanol volume fraction was 0.46, 0.48, and 0.51, respectively. We similarly evaluated the ability of other phospholipids to form stable foam at various concentrations and ethanol volume fractions and found: bovine brain sphingomyelin greater than dipalmitoyl 3-sn-phosphatidylcholine greater than egg sphingomyelin greater than egg lecithin greater than phosphatidylglycerol. The corresponding propensities of different chemical species of phosphatidylcholine to form foam at 40 mg/liter were: dipalmitoyl 3-sn-phosphatidylcholine greater than dioleoyl phosphatidylcholine greater than dimyristoyl phosphatidylcholine greater than dilauroyl phosphatidyl-cho-line.

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