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BNF highlights eGFR failures

The updated BNF will highlight the shortcomings of the estimated glomerular filtration rate calculation for predicting renal disease in patients at extremes of body weight.

The September edition of the BNF will warn that while GPs should use eGFR to estimate the degree of renal function impairment in patients in the normal weight range, the calculation provides anomalous results at either extreme.

Instead, the formulary advises GPs that in patients at both extremes of weight the creatinine clearance should be used, or the dose adjusted according to plasma-drug concentration and clinical response.

Dr Donal O'Donoghue, the Government's renal tsar and a consultant nephrologist at the Hope Hospital in Salford, Manchester, explained that creatinine clearance calculations were ‘normalised' to account for body surface area, whereas eGFR calculations were not.

This, he estimated, could lead to a difference of 10-15% in patients at extremes of the body surface area continuum.

Using eGFR calculations in these patients 'would imply that their renal function is more impaired than it is, which may lead to overdiagnosis of renal disease'.

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