Which Calculation Method of Glomerular Filtration Rate is Suitable in Patients With Normal or Mildly Impaired Renal Function?

We read the article entitled “Association of Glomerular Filtration Rate With Slow Coronary Flow in Patients With Normal to Mildly Impaired Renal Function” by Akin et al ¹ with interest. The authors ¹ concluded that estimated glomerular filtration rate (eGFR) was significantly correlated with slow coronary flow in patients with normal to mildly impaired kidney function.

The Kidney Disease: Improving Global Outcomes organization developed clinical practice guidelines ² in 2012, recommending that the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation is used for reporting eGFR, particularly in patients with a GFR ≥ 60 mL/min/1.73 m². Compared with the Modification of Diet in Renal Disease (MDRD) equation, the CKD-EPI equation may be more accurate in patients with measured ³ GFR ≥ 60 mL/min/1.73m². Additionally, the CKD-EPI study equation more appropriately categorizes individuals at risk of CKD and cardiovascular disease in a middle-aged population with normal or near-normal kidney function. ⁴ It has been shown in several community-based cohorts that people who were reclassified to a higher GFR stage using the CKD-EPI study equation compared with the MDRD study equation had lower risk of adverse events. ^5,6

Estimated glomerular filtration rate overestimates measured GFR when serum creatinine is rising and underestimates measured GFR when serum creatinine is falling. ⁷ Altered muscle mass (eg, reduced by amputation, paraplegia, immobilization, or a neuromuscular disorder and increased by dietary protein intake or creatine dietary supplements), some medications (like aminoglycosides or trimethoprim), and dietary intake (eg, vegetarians) can affect the creatinine levels and eGFR. ⁷ Akin et al ¹ did not mention these factors as exclusion criteria.

Finally, the National Kidney Disease Education Program recommends calibrating serum creatinine measurement to isotope dilution mass spectrometry. ⁸ In the “Laboratory Measurements” section of the article, Akin et al ¹ mention cholesterol, uric acid, and hemoglobin measurements but the most important parameter of this study, creatinine, was not mentioned.

In conclusion, in the light of recently published data, it is probably better to use the CKD-EPI equation to calculate eGFR in patients with near-normal or mildly impaired renal function.