Clinical and prognostic significance of C-reactive protein to albumin ratio in hospitalized coronavirus disease 2019 (COVID-19) patients: Data on 2309 patients from a tertiary center and validation in an independent cohort

C‑reactive protein (CRP) and albumin are inflammation sensitive parameters that are regulated by interleukin‑6 inflammatory pathways. The CRP to albumin ratio (CAR) integrates these two into a potent clinical parameter whose clinical and prognostic association in the context of coronavirus disease 2019 (COVID-19) have not been well defined. We aimed to investigate the clinical and prognostic significance of CAR in the context of COVID-19 infection. We retrospectively analyzed 2309 consecutive COVID-19 patients hospitalized at a tertiary level hospital in the period from March 2020 to March 2021 who had baseline data for a CAR assessment. Findings were validated in an independent cohort of 1155 patients hospitalized from March 2021 to June 2021. The majority of patients (85.8%) had severe or critical COVID-19 on admission. Median CRP, albumin and CAR levels were 91 mg/L, 32 g/L and 2.92, respectively. Higher CAR was associated with a tendency for respiratory deterioration during hospitalization, increased requirement of high-flow oxygen treatment and mechanical ventilation, higher occurrence of bacteriemia, higher occurrence of deep venous thrombosis, lower occurrence of myocardial infarction, higher 30-day mortality and higher postdischarge mortality rates. We defined and validated four CAR prognostic categories (< 1.0, 1.0–2.9, 3.0–5.9 and ≥ 6.0) with distinct 30-day survival. In the series of multivariate Cox regression models we could demonstrate robust prognostic properties of CAR that was associated with inferior 30-day survival independently of COVID-19 severity, age and comorbidities and additionally independently of COVID-19 severity, CURB-65 and VACO index in both development and validation cohorts. The CAR seems to have a good potential to improve prognostication of hospitalized COVID-19 patients. SUPPLEMENTARY INFORMATION: The online version of this article (10.1007/s00508-021-01999-5) contains supplementary material, which is available to authorized users.