Lactate determination in vaginal fluids: a new method in the diagnosis of prelabour rupture of membranes.

OBJECTIVES

To assess whether lactate determination in vaginal fluids, 'Lac test', can be used as a diagnostic test for prelabour rupture of membranes (PROM) and to derive the best cutoff value for a positive test.

DESIGN

Prospective observational study.

SETTING

Labour ward at Söder Hospital in Stockholm, a large clinical service.

POPULATION

Women living in the centre of Stockholm, the capital of Sweden.

METHODS

We selected 200 cases with a history of suspect PROM for determination of lactate concentrations in vaginal fluid. In 100 of these cases, actim PROM tests were also analysed.

MAIN OUTCOME MEASURES

Sensitivity, specificity, positive and negative predictive values, likelihood ratios (LR) and Kappa indices in the identification of visible amniotic fluid at speculum examination.

RESULTS

A lactate concentration > or =4.5 mmol/L was found to be the best cutoff value for a positive test. The 'Lac test' had a sensitivity of 86%, specificity 92%, positive and negative predictive values of 92% and 87%, respectively. Corresponding values for the actim PROM test were 60%, 98%, 97% and 71%. LR for a positive 'Lac test' was 10.75 and for a negative test 0.15. Corresponding values for the PROM test were 30.0 and 0.4, respectively. The Kappa index was higher for the 'Lac test' as compared with the actim PROM test (78% and 59%, respectively).

CONCLUSION

Lactate determination is a valid test in cases with a history of suspect PROM and may even be a better predictor than the actim PROM test.