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Challenges in estimating glomerular filtration rate in diabetic patients

The accuracy of creatinine-based GFR equations has been constantly questioned in many studies conducted in various sub-populations of patients with different types of diabetes and stages of CKD and albuminuria. Both under- and overestimation of eGFR in comparison to mGFR with different creatinine-based equations, including CKD-EPI were documented, dependent on the study design and a comparator method. However, discrepancies between measured and estimated GFR are reflecting physiological differences between actual glomerular function and serum creatinine levels, that are influenced by other factors as well and, more specifically, by hyperglycaemia in diabetic patients. Also, a lack of standardisation and inaccuracies of the methods for measurement of GFR are often overlooked as confounding factors when analysing and interpreting these discrepancies. CKD-EPI equation, offering less biased estimation of GFR than MDRD equation, within a wide range of creatinine levels, may be used as recommended tool for routine eGFR monitoring in diabetic patients. However, clinicians should be aware that mathematically derived eGFR result enables by default a comparison of the patient to the study- population from which the equation was defined and all potential limitations should be carefully considered when interpreting results of eGFR. There is not sufficient evidence at the moment proving cystatin C-derived eGFR might offer any advantage over CKD-EPI eGFR in assessment of kidney function in diabetic patients. In conclusion, while it is not questionable that all eGFR equations suffer from imperfections, an ongoing search for more accurate surrogate markers of kidney function is of utmost importance, as GFR measurement is neither suitable nor available for the recommended routine screening of diabetic nephropathy.

diabetes, eGFR, creatinine, cystatin C

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