The amniotic fluid shake test, also known as the foam stability test, is a quick, inexpensive, qualitative measurement of the amount of pulmonary surfactant contained in the amniotic fluid. It is performed to evaluate FLM. In an obstetric emergency, a primary provider, technician, or nurse can perform it at the bedside so that an immediate decision about delivery can be made. The L/S ratio usually is not determined when the shake test is positive because the shake test also indicates fetal maturity. A table of dilutions is used to determine the stage of lung maturity.
The test is based on the ability of amniotic fluid surfactant to form a complete ring of bubbles on the surface of the amniotic fluid in the presence of 95% ethanol when shaken.
Place a mixture of 95% ethanol and amniotic fluid in an appropriate container and shake for 15 seconds. A commercial kit may be used.
The test is considered negative (lungs are not mature) if no ring of bubbles forms when shaken.
The test has a high false-negative rate but a low false-positive rate. The L/S ratio must be >4:1 for this test to be positive.
Pretest Patient Care
Explain the reason for testing and the meaning of results.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.
Posttest Patient Care
Review test results; report and record findings. Modify the nursing care plan as needed.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.