Fetal Lung Maturity Surfactant, Amniotic Fluid

CPT CODE:

USEFUL FOR:

Predicting fetal lung maturity

SPECIMEN REQUIRED:

10 mL of uncentrifuged amniotic fluid. Send specimen frozen in plastic vial.Note:     Centrifuging the specimen may cause erroneous results.

TRANSPORT TEMPERATURE:

Frozen\Refrig <72 hours OK\Ambient NO

CLINICAL INFORMATION:

During the process of fetal maturation, fetal lungs make surfactant, which prevents the collapse of alveoli by decreasing surface tension. At about the 34th week of gestation, the amount of surfactant increases, indicating that the lungs are mature and ready to support life. In premature birth, there may be inadequate surfactant to allow normal lung function. If delivered prematurely with inadequate lung function, the infant may develop respiratory distress syndrome (RDS).As it is produced, surfactant is secreted into amniotic fluid; therefore, the amniotic fluid surfactant concentration can be used to predict fetal lung maturity.
The classic method (still considered the reference method) for assessing fetal lung maturity is to determine the ratio of lecithin to sphingomyelin (L/S ratio) in amniotic fluid and whether phosphatidyl glycerol (PG) is present or absent. Analysis of the L/S ratio is by thin-layer chromatography (TLC); it is labor intensive and requires a minimum of 4 hours to complete. Conversely, this fluorescence polarization assay, which correlates well with the L/S ratio and PG assay, is automated and requires only 35 minutes to obtain a result.

CLINICAL INTERPRETATION:

A surfactant to phospholipid (S/P ratio) of >55 mg/g indicates lung maturity.
A ratio of <40 mg/g suggests the lungs are immature and the infant may be subject to RDS if delivered.
This assay gives a valid assessment of fetal lung maturity in diabetic as well as nondiabetic patients.

REFERENCE VALUES:

Low: <40 mg/g

Indeterminate: 40-55 mg/g

Mature: >55 mg/g