Amniotic Fluid Tests
Urinalysis and Body
Fluids Review 522
TEST ASSESSMENT/DIAGNOSIS OF METHOD COMMENTS
Lecithin-to-sphingomyelin
( L/S) ratio
Phosphatidylglycerol (PG)
Foam stability index
(shake test)
Lamellar body count
Amniotic fluid bilirubin
Alpha-fetoprotein (AFP)
Reference method. L/S ratio ≥ 2.0 signifies
maturity. False ↑with blood or meconium
contamination.
Last surfactant to rise. Not affected by
presence of blood or meconium.
Index is highest concentration of ethanol
that supports ring of foam after shaking.
Index of 0.48 is comparable to L/S ratio of
2.0. Blood and meconium interfere.
Number correlates with amount of phos-
pholipid present in fetal lungs. Sample
must be free of blood or meconium.
Bilirubin has peak absorbance at 450 nm.
Baseline is drawn connecting 365- &
550-nm points. ΔA 450 compared to gesta-
tional age to determine severity of disease.
Specimen must be protected from light.
Blood & meconium interfere.
High levels with anencephaly, spina bifida.
Fetal lung maturity
Fetal lung maturity
Fetal lung maturity
Fetal lung maturity
Hemolytic disease of the
newborn/fetus
Neural tube defects
Thin-layer chromatography
Immunologic agglutination
Shake with increasing
amounts of 95% ethanol
Count in platelet channel
of hematology analyzers
Direct spectrophotometric
scan from 365–550 nm
Immunologic method
