Detection of Intra-Amniotic Infection
Detection of Intra-Amniotic Infection
Abstract & Commentary
Synopsis: Combining the Gram stain and the amniotic fluid glucose concentration provides the best diagnostic predictive value
Source: Hussey MJ, et al. Am J Obstet Gynecol 1998; 179:650-656.
To determine the diagnostic value of the gram stain and amniotic fluid glucose levels for the detection of intra-amniotic infection in patients with preterm labor or preterm, premature rupture of the membranes (PPROM), Hussey and colleagues performed a prospective study in which all patients underwent amniocentesis. Intra-amniotic infection, defined as a positive amniotic fluid culture, was found in 13.1% of patients overall, 15% (4/26) with PPROM, and 12.7% (16/127) with preterm labor. The organisms most frequently cultured were Ureaplasma urealyticum, Viridans streptococci, E. coli, and group B streptococci. Patients with a positive culture result had a significantly lower gestational age (28.6 weeks) when compared to those with a negative culture, 31.6 weeks. When a positive Gram stain was defined as the presence of either leukocytes and/or bacteria, the sensitivity of this test was 80% with a specificity of 91%, a negative predictive value of 96.8%, and a positive predictive value of 57.1%. Amniotic fluid glucose was significantly lower in patients with a positive amniotic fluid culture, 21.4 mg/dL vs. 31.5 mg/dL. The range of amniotic fluid glucose in the positive culture group was 10 to 45 mg/dL.
Using received-operator characteristic curves, Hussey et al demonstrated that combining the Gram stain and the amniotic fluid glucose concentration provides the best diagnostic predictive value.
Comment by Steven G. Gabbe, MD
The diagnosis of chorioamnionitis is usually based on clinical findings such as maternal fever, uterine tenderness and contractions, and maternal and fetal tachycardia. However, these may be late signs and, since early treatment of intra-amniotic fluid infection is associated with the best maternal and fetal outcomes, other diagnostic approaches have been developed. In many centers, an amniocentesis is routinely performed in patients with PPROM, given the increased risk of intra-amniotic fluid infection particularly early in the third trimester. On the other hand, amniocentesis in cases of preterm labor and intact membranes may be reserved for those patients who continue to contract despite maximum doses of one or even two tocolytics. This study by Hussey et al confirms the value of the amniotic fluid Gram stain and glucose level in detecting patients who will have a positive amniotic fluid culture. Unlike culture results, which might take days to return, the Gram stain and amniotic fluid glucose level can be rapidly obtained. In the presence of infection, amniotic fluid glucose is usually less than 10-15 mg/dL. As shown by Hussey et al, it is helpful to use these tests in combination. For example, with a low amniotic fluid glucose level and a negative Gram stain, the likelihood of intra-amniotic fluid infection is, at most, 20%.
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