Kidney function and cognitive impairment among older hospitalized patients: a comparison of four glomerular filtration rate equations

Background: The relationship between the estimated glomerular filtration rate (eGFR) and cognitive impairment may change as a function of the equation used. We aimed at investigating the association between four different eGFR equations and cognitive impairment among older hospitalized patients. Methods: Our series consisted of 795 older patients consecutively admitted to 7 geriatric and internal medicine acute care wards. The eGFR was calculated by Chronic Kidney Disease Epidemiologic Collaboration (CKD-EPI), Cockcroft-Gault (CG), Berlin Initiative Study (BIS) and Full Age Spectrum (FAS) equations. Study outcomes were total Mini Mental State Examination (MMSE) < 24 and sub-scores related to orientation to time, orientation to space, registration, calculation, three words recall, language and constructional praxis. Statistical analysis was carried out by logistic or Poisson regressions when appropriate. The accuracy of eGFR equations in identifying cognitive outcomes was investigated by calculating the area (AUC) under the receiver operating characteristic (ROC) curve for each equation. Results: After adjusting for potential confounders, eGFR < 30 was significantly associated with MMSE < 24 only with CKD-EPI equation (OR 2.03, 95% CI 1.04–3.96). eGFR < 30 was significantly associated with constructional apraxia with all study equations (CKD-EPI: OR 3.62, 95% CI 1.73–7.56; BIS: OR 2.86, 95% CI 1.31–6.26; FAS: OR 2.83, 95% CI 1.44–5.56; CG: OR 2.08, 95% CI 1.09–3.99). The accuracy of eGFR < 30 in identifying patients with defective constructional praxis was poor with all (BIS: AUC 0.54, 95% CI 0.52–0.55; CKD-EPI: AUC 0.55, 95% CI 0.53–0.57; CG: AUC 0.58, 95% CI 0.55–0.61; FAS: AUC 0.56, 95% CI 0.54–0.58). Conclusions: Constructional apraxia may characterize the cognitive profile of older patients with severe CKD. The accuracy in identifying patients with constructional apraxia is only fair, and studies including other biomarkers of kidney function are needed.