Background: The prevalence of CKD rises with age. The prevalence of CKD-related metabolic complications in the oldest old in relation to different GFR estimations is largely unknown. eGFR-based thresholds for the detection of these complications remain uncertain.
Methods: A cross-sectional analysis embedded within the BELFRAIL study, a population-based prospective cohort study of the oldest old in Belgium, was performed. The prevalence of anemia, elevated serum parathyroid hormone (PTH), high serum phosphorus and low uncorrected serum calcium was analyzed in relation to GFR estimated by three serum creatinine-based equations and one cystatin C-based equation.
Results: 567 patients aged 80 and over were included (63% women). The prevalence of anemia, elevated PTH and high phosphorus showed an inverse relationship with eGFR. This relationship remained after logistic regression analysis adjusting for demographics and co-morbidity. No such relationship between low calcium and eGFR was found. Using an eGFR of 60 ml/min/1.73 m(2) modification of diet in renal disease equation (MDRD) as screening threshold for metabolic complications would result in a high incidence of missed complications: 29%, 28% and 40% for anemia, elevated PTH and high phosphorus, respectively.
Conclusion: The presence of anemia, an elevated PTH or an elevated serum phosphorus level increased with lower eGFR but even among patients with an eGFR >60 ml/min/1.73 m(2), these complications are common. Thus this eGFR cut-off appears inadequate for patients aged 80 and over. How the oldest old may be screened appropriately for these CKD-related complications requires further investigation.
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