Neutrophil-lymphocyte ratio: a marker for microbial invasion of amniotic cavity in preterm prelabor rupture of membranes

This study aimed to assess the association between maternal blood neutrophil-to-lymphocyte ratio (NLR) and microbial invasion of the amniotic cavity (MIAC) and to compare the diagnostic performance of NLR with that of maternal serum C-reactive protein (CRP) levels for identifying MIAC in patients with preterm prelabor rupture of membranes (pPROM). This study included 154 patients with pPROM who underwent transabdominal amniocentesis (gestational age: 20–33 weeks) to evaluate the microbiologic status of amniotic cavity and/or fetal lung maturity. The amniotic fluid (AF) was cultured for aerobic and anaerobic bacteria and genital mycoplasmas. MIAC was defined as a positive AF culture. Maternal blood samples were collected within 24 hours of amniocentesis, and serum levels of leukocyte differentials and CRP were measured. 1) The rate of MIAC was 36.4% (56/154) in patients with pPROM; 2) the median NLR and CRP levels in the patients with MIAC were significantly higher than those without MIAC (NLR: 6.8 [95% CI, 7.0–9.8] vs. 5.0 [95% CI, 5.3–6.6], P < 0.05; CRP levels: 0.6 mg/dL [95% CI, 0.8–1.3] vs. 0.3 mg/dL [95% CI, 0.5–0.9], P < 0.05); 3) the area under the curve of NLR was similar to that of CRP (0.7 [95% CI, 0.6–0.8] vs. 0.6 [95% CI 0.5–0.7], P=0.59); 4) the NLR ≥ 6.2 had sensitivity of 64.3% (95% CI: 50.4–76.6), specificity of 65.3% (95% CI, 55.0–74.6), positive likelihood ratio of 1.9 (95% CI, 1.3–2.6), and negative likelihood ratio of 0.55 (95% CI, 0.4–0.8); 5) the rate of MIAC was 54.3% (19/35) in patients with high NLR (≥ 6.2)/high CRP (≥ 0.7mg/dL), 48.6% (17/35) in those with high NLR/low CRP, 40.0% (8/20) in those with low NLR/high CRP, and 18.8% (12/64) in those with low NLR/low CRP (odds ratio [OR], 5.15 [95% CI, 2.06–12.84], 4.09 [1.64–10.20] and 2.89 [0.97–8.62] compared to patients with low NLR/low CRP, respectively). An elevated NLR was associated with the presence of MIAC in patients with pPROM. The diagnostic performance of NLR was similar to that of CRP levels. However, MIAC was present in 18.8% of patients with low NLR/low CRP levels.