To verify the role of lactate dehydrogenase to albumin (LDH/ALB) ratio as an independent prognostic factor for mortality due to the lower respiratory tract infection (LRTI) in the emergency department (ED).

We reviewed the electronic medical records of patients who were admitted to the ED for the management of LRTI between January 2018 and December 2020. Initial vital signs, laboratory data, and patient severity scores in the ED were collected. The LDH/ALB ratio was compared to other albumin-based ratios (blood urea nitrogen to albumin ratio, C-reactive protein to albumin ratio, and lactate to albumin ratio) and severity scales (pneumonia severity index, modified early warning score, CURB-65 scores), which are being used as prognostic factors for in-hospital mortality. Multivariable logistic regression was performed to identify independent risk factors.

The LDH/ALB ratio was higher in the non-survivor group than in the survivor group (median [interquartile range]: 217.6 [160.3;312.0] vs. 126.4 [100.3;165.1], p < 0.001). In the comparison of the area under the receiver operating characteristic curve (AUC) for predicting in-hospital mortality, the AUC of the LDH/ALB ratio (0.808, 95% confidence interval: 0.757–0.842, p < 0.001) was wider than other albumin-based ratios and severity scales, except the blood urea nitrogen to albumin ratio. In the multivariable logistic regression analysis, the LDH/ALB ratio independently affected in-hospital mortality.

The LDH/ALB ratio may serve as an independent prognostic factor for in-hospital mortality in patients with LRTI.