To study the association between risk for hospitalisation in an elderly population related to renal function, number of chronic diseases and number of prescribed drugs.

A case–control study. Persons hospitalised were included and their controls were obtained from electronic hospital medical records. If data were lacking on creatinine levels, multiple imputation was used.

Blekinge County in southwestern Sweden.

Study of individuals aged 75 years or older in 2013. We identified a total of 2,941 patients with a first hospitalisation. Of these, 81 were excluded, 78 due to incomplete data and 3 because of lack of control persons. Controls were matched to the same sex and birth year, which resulted in 5720 persons.

To analyse the OR for hospitalisation conditional logistic regression was used.

A total of 695 persons lacked creatinine value. Using imputation values comparing persons with estimated glomerular filtration rate (eGFR) 2 with ≥30 univariate analyses showed an increased OR 2.35 (95% CI 1.83 to 3.03). Adjusted analyses demonstrated an OR of 1.90 (95% CI 1.46 to 2.47). Comparing eGFR2 against ≥45 univariate analyses showed OR 1.38 (95% CI 1.22 to 1.57). Adjusted analyses OR for the same group were 1.17 (95% CI 1.03 to 1.33). In both models, the OR for five or more chronic conditions and five or more medications showed a statistically increased risk for hospitalisation.

There is a need for systems using data collected in routine care to follow elderly patients to minimise avoidable hospitalisations that can cause adverse effects. Renal function, number of chronic conditions and medications are factors that are of significant importance. This study demonstrates the complexity of this patient group.