[Clinical application of neutrophil/lymphocyte count ratio in the diagnosis of lung bacterial infections in the elderly].

OBJECTIVE: To investigate the clinical application of neutrophil/lymphocyte count ratio in the diagnosis of lung bacterial infections in the elderly. METHODS: Complete blood count (CBC), white blood cell volume- conductivity-scatter (VCS) parameters, C-reactive protein (CRP) and neutrophil CD64 index (CD64 index) of patients older than or equal to 60 years with pulmonary bacterial infections (n=140), tuberculosis (n=35), non-lung bacterial infections (n=86), no infections or controls (n=100) and healthy people (n=278) were detected. Neutrophil/lymphocyte count ratio (NLCR) is calculated through the percentage of neutrophils (NE) divided by the percentage of lymphocytes (LY). RESULTS: Youden Index of NLCR (46.1%) was greater than that of WBC, NE and CD64, and second only to CRP (53.5%) by means of comparison of multiple parameters for diagnosis of bacterial infections in part of cases. After the increase in the number of cases and types of the disease, the CRP levels of pulmonary bacterial infections, tuberculosis, non-lung bacterial infections, no infections or controls were 31.5 (11.3-104.8), 3.7 (1.5-12.7), 41.7 (10.5-82.4), 2.4 (1.2-4.0) mg/L, respectively. NLCR levels of them were 6.9 (3.2-13.8), 2.7 (1.8-3.6), 4.5 (3.0-9.0), 2.2 (1.7-2.9), 1.7 (1.4-2.0); WBC levels of those groups were 7.4 (5.7-11.1)×10(9)/L, 6.2 (5.3-7.1)×10(9)/L, 6.5 (5.2-8.5)×10(9)/L, 5.7 (4.7-6.9)×10(9)/L, 6.0 (5.3-6.8)×10(9)/L; NE levels of those groups were 79.2 (65.7-85.0)%, 63.3 (55.9-69.1)%, 74.0 (65.3-82.6)%, 62.1 (55.3-66.7)%, 56.4 (51.8-60.6)%, respectively. The differences were statistically significant (Chi-square value=162.628, 277.763, 49.653, 218.758, P<0.001); CRP, NLCR, WBC, NE of patients with pulmonary bacterial infections were significantly higher than non-lung bacterial infections and the controls (P<0.001). There was no difference in CRP, WBC, NE and NLCR levels between lung bacterial infections and tuberculosis (P>0.05). The sensitivity of NLCR for diagnosis of pulmonary bacterial infections was 77.0%, which is equal to CRP, and higher than that of WBC, NE. There was a high sensitivity (87.1%) for diagnosing pulmonary bacterial infections in the elderly by combination of NLCR and CRP. The sensitivity of NLCR for diagnosis of pulmonary bacterial infections was 67.7%, which was higher than that of NE (43.4%) in patients with lung bacterial infections had a normal WBC. Although the correlation between NLCR and types of bacterial infections had not been found, the positive rate of bacterial culture of patients with increased NLCR (40.2%) was much higher than that with normal ones (9.1%). NLCR levels of patients with poor prognosis was 11.2 (7.4-26.1), which is significantly higher than that of patients with good prognosis in cases with pulmonary bacterial infections (Z=-3.460, P=0.001). CONCLUSIONS: NLCR is a simple, rapid and economic parameter of blood leukocyte, which is helpful in diagnosis and differentiation of elderly patients with lung bacterial infections, especially the cases without increasing WBC. NLCR, combined CRP can improve the diagnostic sensitivity for lung bacterial infections, and that be used for the prognostic evaluation of patients with pulmonary bacterial infections in the elderly.