Measuring renal function in older patients

Van Pottelbergh, Gijs [UCL] Wallemacq, Pierre [UCL] Demoulin, Nathalie [UCL] Hoste, Liesbeth [KULAK] Boland, Benoît [UCL] Pottel, Hans [KULAK] Jadoul, Michel [UCL] Degryse, Jean-Marie [UCL] et al.[show all]

The glomerular filtration rate (GFR) is a well-accepted marker of renal function. However, the use of gold-standard tests to measure the GFR is difficult in clinical practice. As an alternative, creatinine or cystatin C plasma concentrations are often used to estimate the GFR. However, the GFR estimations are not well validated in older patients. Older (>65 year) participants were recruited by their physician. All participants received an injection of 2, 5 ml iohexol, and eight timed blood samples were collected 20 to 600 min. after the injection to calculate the true GFR. The creatinine and cystatin C serum concentrations were measured and were used to estimate the GFR using the Cockcroft–Gault (CG), MDRD and three CKD-EPI equations (creatine and/or cystatin C based). The eGFR values were compared with the true GFR. The study included 36 participants (14 males, mean age 83 years and mean true GFR 49 ml/min/1.73 m²). On average, the MDRD, CKD-EPIcreat and CKD-EPIcyst equations overestimated the mGFR by 7.8, 3,6 and 8.0 ml/min/1.73 m², respectively, and the CKD-EPIcreatcyst and CG equation underestimated the mGFR by 8.4 and 13.6 ml/min/1.73 m² respectively. All equations differed by more than 30% compared with the true GFR in at least 17 out of 36 participants. There is an urgent need for a more accurate GFR estimation equation in elderly and very elderly patients.