The neutrophil index — Lymphocyte and its usefulness in the early diagnosis of infection in elderly patients. Cohort study

Abstract

The classical infectious markers, including clinical presentation and standard biomarkers, have poor sensitivity and specificity in elderly patients. This is highly detrimental in this population because infection prognosis is related to early diagnosis and treatment. The neutrophil–lymphocyte ratio (PNN/Ly ratio) is an emerging marker of infection with good performance for diagnosis of community-acquired infections, but it has never been evaluated in a geriatric population. Objective: To evaluate the sensitivity and specificity of the PNN/Ly ratio for early diagnosis of an infectious condition in patients above 80 years-old admitted in acute medicine department via the emergency department. Methods: A retrospective cohort study performed on all patients above 80 years-old admitted in an acute medical unit of a French University Hospital Internal Medicine Department. All patients came from the emergency department and had early routine full blood count at admission. We performed a retrospective confirmation of the physician's diagnosis of infection based upon association of one or more of the following criteria: general symptoms, clinical proven or probable source of infection, inflammatory syndrome (including increased CRP), radiological arguments and a favorable outcome with antibiotic therapy. Sensitivity and specificity of the neutrophil–lymphocyte ratio at hospital admission (emergency department) to the final diagnosis of infection was expressed as AUROC curve in SPSS 14 and the contribution of this test in addition to the usual markers for the early diagnosis of infection was tested in a binary logistic regression model. Results: Between November 2011 and May 2012, 151 patients with a mean age of 85.7 SD = 4.12 years, 60.3% women were admitted in the acute internal medicine unit. The mean modified Charlson score of 8.23 +/− 2.73 testifies in favor of a heavily comorbid population. An infection diagnosis was retrospectively validated in 91 of these 151 patients (59%): pulmonary in 59 cases, urinary tract infection in 17, intra-abdominal in 8 and in other sites for 7. If all patients had a routine full blood count at admission in the emergency department, early inflammatory blood markers as CRP were performed in 135 out of the 151 (89%) patients. Statistical analysis comparing multiple variables including temperature upon emergency department admission, CRP, white blood cells, neutrophil count, lymphocytes and the PNN/Ly ratio showed that the area under the receiver operating curve for infection prediction was 0.799 (95% CI 0.718–0.880) for PNN/Ly ration as compared at 0.877 (95% CI 0.811 to 0.942) for CRP and 0.748 (95% CI 0.663–0.832) for neutrophil count. Binary logistic regression model, showed that adding the PNN/Ly ratio to temperature, white blood cell count and CRP measurement increases sensitivity for early infection diagnosis from 75.6% to 84.4% and specificity from 82.9% to 84.4%. Conclusion: In very old patients, in addition to usual markers, neutrophil and lymphocyte count and neutrophil to lymphocyte ratio done at the time of admission in the emergency department, improve the accuracy of infection diagnosis. This may improve early and active efficient therapy and global outcome.