 Intra-amniotic infection is characterized  by an increase in the total amniotic fluid LDH activity and a specific  upregulation of LDH isoforms-3, -4 and -5.  We sought to determine the  utility of vaginal amniotic fluid (vAF) total LDH activity and its  specific isoform profile in predicting infection in women with PPROM.

 49 Consecutive women (GA=29.5 ± -0.5  wks) with PPROM underwent vaginal "pool" sample collection followed by  amniocentesis (aAF). aAF was cultured for acrobic, anaerobic, 

  species. Women were stratified into 2 groups: (i) positive amniotic  fluid cultures (+AFC, n=22) and (ii) negative amniotic fluid cultures  (-AFC, n=27). In paired aAF-vAF samples the total LDH activity was  determined by a kinetic UV spectrophotometric assay. The LDH isoform  activity was investigated using isoelectric focusing in agarose gels.

 1) In women with -AFC, the total LDH  activity was higher in vAF compared to aAF (median [range] vAF:639.6  [45.8-1,368.0] vs. aAF: 177.4 [47.5-2,217.2] U/L, p<0.001). This  increase was attributed to a selective upregulation of LDH isoforms -4,  and -5 (p<0.05); 2) In patients with +AFC, the total LDH activity was  increased in both aAF and vAF, though to a greater extent in the  vaginal "pool" samples (vAF: 1,312.5 [157.4-2,739.3] vs. aAF: 414.7  [74.9-2569.9] U/L, p<0.001). The increase in total LDH activity in  vAF was attributed to the upregulation of LDH isoforms -1, -2, -3 and  -4; 3) The vAF total LDH activity ≥ 1000  U/L had a sensitivity, specificity, PPV and NPV of 68%, 93%, 88% and  78% respectively, for diagnosing +AFC; 4) The accuracy of the vAF LDH  activity in diagnosing a +AFC was similar to that of the aAF (vAF; 82%  vs. aAF: 73%, p=0.417). The test performance was independent of the  rupture-to-amniocentesis interval or GBS colonization.

 vAF total LDH activity can accurately  diagnose intra-amniotic infection. The increase in total LDH activity in  vAF in response to intra-amniotic infection is due to an upregulation  of a different panel of LDH isoenzymes compared to that in aAF.

American Journal of Obstetrics and Gynecology

Volume 195, Issue 6, Supplement S (December 2006)