The ideal marker for measuring GFR: what are we looking for?

Area of Science:

• Nephrology
• Geriatric Medicine
• Nuclear Medicine

Background:

• Accurate assessment of kidney function, particularly glomerular filtration rate (GFR), is crucial.
• Estimating GFR in the elderly population using standard formulas presents significant challenges.
• This study addresses the need for reliable GFR estimation methods in older adults.

Purpose of the Study:

• To evaluate the accuracy of commonly used formulas for estimating GFR in the elderly.
• To compare estimated GFR (eGFR) values with directly measured GFR (mGFR) using a reference method.
• To identify the most accurate eGFR formulas for this demographic.

Main Methods:

• A cohort of 85 elderly patients (average age 76.2 years) was studied, with 42% having pre-existing chronic kidney disease (CKD).
• Glomerular filtration rate was directly measured using the 99mTc-DTPA renogram and Charles D. Russell's two-sample method.
• Estimated GFR values were calculated using the MDRD, Cockcroft-Gault, CKD-EPI, and BIS1 formulas based on serum creatinine levels.

Main Results:

• Concordance between measured GFR and estimated GFR varied by formula: MDRD (57.5%), Cockcroft-Gault (48.3%), CKD-EPI (49.4%), and BIS1 (58%).
• The MDRD and BIS1 formulas demonstrated higher concordance with the directly measured GFR values.
• Cockcroft-Gault and CKD-EPI formulas showed lower agreement with the reference method in this elderly cohort.

Conclusions:

• The MDRD and BIS1 formulas provide more accurate estimations of glomerular filtration rate in the elderly population compared to Cockcroft-Gault and CKD-EPI.
• Direct measurement of GFR using 99mTc-DTPA and the Russell method serves as a reliable reference.
• Further validation of GFR estimation formulas in diverse elderly populations is warranted.