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Formula to calculate eGFR miclassifies in obesity

By Lilian Anekwe

The most commonly used formula to calculate eGFR in obese patients with type 2 diabetes underestimates the something, according to UK researchers.

Researchers at the University of Liverpool recruited 111 patients with type 2 diabetes and CKD stages 1-4, 74 of whom were obese with a BMI >30 kg/m2. All participants had their GFR estimated by the gold-standard isotopic GFR, and estimated using the medication of diet in renal disease (MDRD) equation.

The difference in eGFR and isotopic GFR was -22.4 in the obese group compared with -6.04 in the non-obese group, a statistically significant difference. The bias remained significant when the GFR had been indexed to a body surface area of 1.73m2, at -9.4.

The bias resulted in a misclassification of patients with later-stage CKD. 40% of participants in CKD stage 2 were misclassified into stage 3 and 54% from stage 3A to stage 3B.

Professor John Wilding, head of the department of obesity and endocrinology at the University of Liverpool, concluded: ‘There is a need for better equations for estimating GFR in obese individuals. Until such an equation becomes available, clinicians should consider this bias when making treatment decisions in obese patients with type 2 diabetes.'

Diabetologia 2011, online February 25

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