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

The purpose of this study was to determine the value of amniotic fluid white blood cell count in the diagnosis of microbial invasion of the amniotic cavity. Amniotic fluid was retrieved by amniocentesis from 195 patients with preterm labor and intact membranes. Fluid was cultured for aerobic and anaerobic bacteria, as well as for mycop asmas. The prevalence of a positive amniotic fluid culture was 12.8% ( 25 195). Patients with a positive amniotic fluid culture had a significantly higher median amniotic fluid white blood cell count than did patients with a negative amniotic fluid culture (median, 6 cells/mm³; range, 0 to 11,000 cells/mm³ vs median, 320 cells/mm³; range, 1 to 4480 cells/mm³; p < 0.0001). An amniotic fluid white blood cell count ≥50 cells/mm³ had a sensitivity of 80% ( 20 25), a specificity of 87.64% ( 149 170), a positive predictive value of 48.78% ( 20 41), and a negative predictive value of 96.75% ( 149 154) in the detection of a positive amniotic fluid culture for microorganisms. Although the sensitivity of an amniotic fluid white blood cell count (≥50 cells/mm³) in the detection of microbial invasion of the amniotic cavity was greater than that of the Gram stain of amniotic fluid (80% [ 20 25] vs 48% [ 12 25]; p < 0.05), the specificity was lower (87.64% [ 149 170] vs 98.8% [ 168 170]; p < 0.05). However, 88% ( 15 17) of all patients with an amniotic fluid white blood cell count ≥50 cells/mm³ and a negative amniotic fluid culture had a spontaneous preterm delivery. We conclude that the amniotic fluid white blood cell count is a sensitive, simple, and inexpensive test for the detection of microbial invasion of the amniotic cavity. An elevated amniotic fluid white blood cell count is a risk factor for preterm delivery.