Estimating renal function in older people: a comparison of three formulas

Area of Science:

• Geriatric Medicine
• Nephrology
• Clinical Pharmacology

Background:

• Estimating glomerular filtration rate (GFR) is crucial for managing renal insufficiency, which is linked to higher mortality and morbidity.
• Previous observations suggest discrepancies between the Cockcroft-Gault (CG) and Modification of Diet in Renal Disease (MDRD) formulas in older populations.

Purpose of the Study:

• To compare GFR estimates in elderly inpatients (aged 65+) using the CG formula and two MDRD formulas.
• To assess the agreement and potential interchangeability of these formulas for renal function assessment in this demographic.

Main Methods:

• Study involved 7,747 inpatients aged 65 or older from acute care geriatrics and internal medicine wards.
• Agreement between CG, MDRD1, and MDRD2 formulas was quantified using 95% limits of agreement, kappa statistic, and graphical analysis.
• Potential confounders influencing GFR estimate differences, such as age and weight, were evaluated.

Main Results:

• Mean GFR estimates were 51.2 ml/min (CG), 54.9 ml/min (MDRD1), and 64.7 ml/min (MDRD2).
• Individual GFR estimates from MDRD formulas could differ by over 50% compared to the CG formula.
• Moderate agreement was found for diagnosing moderate renal insufficiency, and fair agreement for severe insufficiency, influenced by age and weight.

Conclusions:

• While CG and MDRD formulas demonstrate good average agreement for GFR estimation in the elderly, individual estimates can differ substantially.
• These formulas should not be used interchangeably for measuring renal function in older individuals due to significant individual variability.
• Clinical decisions regarding renal function in the elderly require careful consideration of the chosen estimation formula.