Association between biomarkers at discharge and risk of readmission after community-acquired pneumonia – a retrospective cohort study

Background: Readmission after community-acquired pneumonia (CAP) is common but knowledge about risk factors is limited. Objective: To investigate whether haemoglobin, white blood cell count (WBC), urea, sodium, albumin, and C-reactive protein (CRP), measured at discharge in patients with CAP are associated with 30-day readmission. Methods: This study was a Danish, retrospective, multi-centre, cohort study of patients hospitalised with CAP. The outcome was all-cause, unplanned, 30-day readmission. Biomarkers were measured at discharge and evaluated as categorical variables in the statistical analyses: For WBC, urea, and CRP, the highest quartile was compared to the 3 lowest quartiles (reference), and for haemoglobin, sodium, and albumin, the lowest quartile was compared to the 3 highest quartiles (reference). Sub-distribution hazard ratios (sHR) were calculated for biomarkers and baseline variables using regression models with death without readmission as a competing risk. Results: Of the 1149 patients discharged alive, 184 (16.0 %) were readmitted within 30 days. Elevated WBC (sHR: 1.50; 95 % CI, 1.07-2.11), low albumin (sHR: 1.78; 95 % CI, 1.24-2.54) and the presence of ≥ 2 co-morbidities (sHR: 1.74; 95 % CI, 1.15-2.64) were independently associated with readmission. When combining co-morbidities, WBC and albumin, there was an increasing risk of readmission for patients with 1, 2 or 3 risk factors with sHR of 1.76 (95 % CI, 1.25-2.49), 2.59 (95 % CI, 1.71-3.93) and 6.15 (95 % CI, 3.33-11.38), respectively. Conclusion: WBC and albumin measured at discharge were independently associated with 30-day readmission in patients with CAP.