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Foam Stability Index Test

Description

This is a qualitative bedside test in which the presence of surfactant results in persistence of bubbles after shaking. Ethanol acts as an antifoaming agent. The higher the amount of surfactant, the greater the resistance to the antifoaming action of ethanol.


 

Specimen: Amniotic fluid, protected from light

 

Testing: Amniotic fluid is added to 6 tubes containing various concentrations of ethanol (final concentrations range from 44% to 50%). The tubes are shaken for 30 seconds, left to stand for a given period and are then examined for a complete ring of bubbles along the meniscus. With fetal maturity sufficient surfactant is present to withstand 47% ethanol concentrations.

 

Interpretation:

• A foam stability index >= 0.47 is considered positive and indicates fetal maturity.

• A negative test does not always indicate fetal immaturity.

 

Interferences:

(1) blood

(2) meconium

 


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Specialty

ICD-10