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Lab delays add to fears over CKD misdiagnosis

Doubts over the testing procedures for chronic kidney disease have been reignited by a study finding patients were being wrongly labelled with the condition because of delays in processing blood samples.

The findings follow those released earlier in the year showing eating cooked meat in the four hours before a blood test suppressed eGFRs by enough to diagnose a patient with no renal impairment as having stage 3-5 CKD.

Taken together, these two sources of error could mean significant numbers of patients diagnosed with the disease actually have normal kidney function. The researchers warned their findings could be a 'huge issue' for rural GPs in particular after finding delays of 10 hours or more in laboratory analysis of creatinine levels led to a misdiagnosis of CKD in more than a fifth of cases.

Dr Eric Kilpatrick, a researcher on the study and consultant chemical pathologist at Hull Royal Infirmary, said rural GPs should note the date and time a blood sample was taken and ensure it arrived at the lab quickly to prevent false positive diagnoses of CKD. His study exposed multiple blood samples from 21 patients to varying delays prior to centrifugation before creatinine analysis, and found levels increased over 24 hours. Out of 21 samples delayed by more than 10 hours, four showed misclassification of kidney disease.

Dr Kilpatrick said: 'This is part of a series of problems with CKD diagnosis – all you need is a protein meal and then to go to your rural GP and you get a wrong diagnosis. If GPs are in an urban area it is probably not an issue, but in rural areas it can be a huge issue. Some rural practices have a centrifuge, so maybe others should think about that. Once blood is centrifuged it shouldn't be a problem.'

The finding of another potential source of error in GP diagnosis of CKD will adds to suspicions that many patients are being misdiagnosed and treated unnecessarily. Dr Harry Yoxall, a GP in Somerset and secretary of Somerset LMC, said: 'It's another confounding factor in what is already a very complicated area.'

But he added: 'In Somerset most practices are linked to their nearest DGH by a courier service. Most practices that are a long way from the hospital will be centrifuging.'

The study was published in this month's Annals of Clinical Biochemistry.

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