Elevated blood urea, independent of glomerular filtration rate (GFR), confers increased risk of adverse functional outcome in elderly hip fracture patients

This retrospective cohort study investigated the possible interrelations of GFR and functional outcome in elderly hip fracture patients. The final analyses comprised 499 consecutive patients undergoing standard medical, surgical and rehabilitation treatment in an orthogeriatric unit of a tertiary care hospital. Functional outcomes were assessed by Functional Independence Measurement (FIM™) scores. Kidney function was assessed by blood urea and creatinine, as well as by GFR according to the modification diet of renal disease study (MDRDS) formula. Mean age was 83.60 ± 5.14 and mean GFR 61.07 ± 17.22 ml/min. GFR was <60 ml/min in 91.8% out of all patients. FIM admission and discharge scores, and gains, were not associated with GFR values, except for discharge motor FIM which was significantly higher in patients with GFR greater than 30 ml/min (p = 0.043). In regression analysis, GFR was associated with motor FIM at discharge (β = 0.028, p = 0.022). Neither GFR nor creatinine was associated with discharge total FIM. In contrast, lower admission urea levels were predictive of higher motor (correlation coefficient (CC) = 0.151, odds ratio (OR) 0.132, 95% confidence interval (CI) = 0.027–0.237, p = 0.013) and total FIM scores (CC = −0.022, OR = 0.978, 95%CI = 0.960–0.997, p = 0.022) at discharge. We suggest that GFR and creatinine are poorly associated with functional outcome. Instead, urea is more likely to predict functional outcome, and may serve as more reliable biomarker for the prognostication of functional outcome.