Amniotic fluid white blood cell count: a rapid and simple test to diagnose microbial invasion of the amniotic cavity and predict preterm delivery

Accurate, rapid diagnosis of the presence of microbes in the amniotic fluid is essential to prevent complications, which can include premature delivery and a host of problems for both mother and infant. However, many medical centers that use amniocentesis (sampling of amniotic fluid) analyze their samples using the Gram stain, a microbiological method that can fail to detect microorganisms in as many as half the cases in which they are present. In this study, the amniotic fluid white blood cell count was evaluated as a method of diagnosing microbial invasion. Amniotic fluid samples were taken from 195 patients undergoing preterm labor with a single fetus; the patients underwent treatment with tocolytic agents (to inhibit uterine contractions). The samples were evaluated with the Gram stain and in tissue culture, as well as for concentrations of white blood cells. Pregnancies progressed to term in 84 cases (43 percent) and microorganisms were present in 25 cases (12.8 percent). Those with positive culture results had higher levels of white blood cells than those with negative results. The sensitivity of the white blood cell count (extent to which that test correctly identified the infected women) was 80 percent; and its specificity (extent to which the test correctly diagnosed the absence of infection) was 87.6 percent. The sensitivity of the white blood cell count was higher than that of the Gram stain, but its specificity was lower. On the whole, the amniotic fluid white blood cell count is sensitive, simple, and inexpensive. Patients with levels equal to or less than 50 cells per cubic millimeter were at risk for premature delivery. (Consumer Summary produced by Reliance Medical Information, Inc.)