Significance of blood cultures in nursing home-acquired pneumonia.

Abstract

The significance of blood cultures in nursing home-acquired pneumonia (NHAP) is incompletely understood. We retrospectively analyzed the clinical and laboratory features of 515 patients with NHAP admitted to our hospital over an 11-year period. Blood cultures were obtained from 336 patients (65.2%). We compared 13 and 323 patients with positive and negative blood cultures, respectively. The former showed lower systolic blood pressure and higher blood urea nitrogen (BUN), creatinine, C-reactive protein (CRP), and A-DROP scores than the latter. With regard to A-DROP parameters, patients with positive blood cultures showed significantly higher rates of dehydration (BUN≥21mg/dL) and low blood pressure (systolic blood pressure≤90mmHg). Multivariate analysis identified CRP values and low blood pressure as independent predictors of bacteremia: CRP (odds ratio [OR] 1.11; 95% confidence interval [CI] 1.04-1.19, P=0.003) and low blood pressure (OR 6.03; 95% CI 1.06-34.25, P=0.04). A receiver operating characteristic curve indicated that CRP was of moderate accuracy (area under the curve=0.75), and its diagnostic accuracy was optimal at a cut-off point of 19.2mg/dL (sensitivity 69%, specificity 87%). Since the probability of true bacteremia is very low in NHAP, obtaining blood cultures from all patients with NHAP is unnecessary. However, our results suggest blood cultures are warranted from patients with high CRP values (≥20mg/dL) or low blood pressure.