[Diagnosis of anaerobic infection of the pleural fluid using gas-liquid chromatography].

Background: An assessment of the efficacy of the detection of volatile and non-volatile fatty acids that are produced by microorganisms aimed at the possible diagnosis of pleural empyema.

Methods: 106 pleural fluids were examined by gas-liquid chromatography in contrast to conventional aerobic and anaerobic cultures. The sample previously prepared (1 microliter) was injected in an Hewlett-Packard 5890 chromatograph, that was equipped with a fused silica capillary column and a flame ionization detector.

Results: Growth of aerobic or anaerobic microorganisms was obtained in 13 (12.3%) of the samples, and volatile or non-volatile fatty acids were detected in all of them (sensitivity = 1). No growth was obtained in the 93 samples, but volatile or non-volatile fatty acids were detected in 64 (68.8%) of them (specificity = 0.31). A positive predictive value of 0.17 and a negative predictive value of 1 were obtained. Growth of anaerobic microorganisms was obtained in 9 samples (8.5%) and volatile fatty acids were detected in all of them (sensitivity = 1). Anaerobic microorganisms did not grow in 97 samples, however volatile fatty acids were detected in 2 (2.1%) of them. A positive predictive value of 0.82 and a negative of 1 were obtained.

Conclusions: Referring to pleural fluid samples, the detection of volatile and non-volatile fatty acids by gas-liquid chromatography is a highly sensitive method, that may be used to quickly reject negative samples in about 30 mins. Furthermore, when anaerobic microorganisms exist, the high specificity of gas-liquid chromatography will make it possible to confirm their presence in the sample, mainly if there is a clinical suspect of anaerobic infection. Thus, the utilization of this sensitive method may also change the therapeutic behaviour.