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Eating cooked meat suppresses eGFRs by a third, analysis reveals

Food effect drives mass over-diagnosis of CKD

GPs are likely to be greatly over-diagnosing chronic kidney disease because of the effects of food on serum creatinine blood tests.

Eating cooked meat in the four hours before a blood test dramatically suppresses eGFRs – by enough to diagnose a patient with no renal impairment as having stage 3-5 CKD – a new study reveals.

The researchers called for changes to guidelines to take into account the effects of food.

Median eGFRs in the study fell from 84 before eating meat to 59.5 one to two hours afterwards and 64 three to four hours afterwards.

Dr Ian Godber, a researcher on the study and principal biochemist at Wishaw General Hospital in Lanarkshire, warned: 'If somebody is a regular meat-eater and has a cooked meat meal most days their report sample will be skewed. It will skew your eGFR in the wrong direction.'

The researchers studied blood samples from 32 patients before and after eating a normal sized meat-containing meal. They argued in a letter in the BMJ that GPs should retest for suspected kidney disease either on a fasting sample or where no cooked meat had been eaten.

Professor Mike Kirby, a GP with an interest in kidney disease and professor in health and human sciences at the University of Hertfordshire, said the research would take GPs by surprise: 'Ninety-nine per cent of GPs are not putting this into the equations at the moment.

'Practices are compiling registers and looking retrospectively at creatinine so there won't be any record of whether the sample was fasting or not.'

A second study in the British Journal of Clinical Pharmacology added to confusion over eGFR after finding it is also suppressed by hormonal contraception.

Dr Jo Richardson, a GP in the Isle of Dogs, London, summed up the feelings of many GPs in a response to the BMJ.

'Routine reporting of eGFR with every serum creatinine seems to have led to three outcomes in general practice: worried patients, increased workload and confused clinicians.'

• Eating cooked meat within four hours of a blood test can skew eGFR results

• If CKD is suspected, retest either on a fasting sample or after a meal that does not contain meat

• Hormonal contraception can suppress eGFR by 6.3 per cent

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