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A faulty production line

Blood test errors to rise with centralised pathology labs

By Nigel Praities

GPs may be faced with huge numbers of inaccurate blood test results as samples are transported longer distances to centralised pathology services, researchers are warning.

A four-year audit of GP-requested potassium tests found as many as one in five were false positives at certain times of the year, because of the effects of cold weather.

And the researchers predicted the problem would get worse as hospitals looked to consolidate pathology services and samples were transported further.

The audit, conducted in Bromley, south London, found an average of 9% of potassium results were too high, rising to 17% in cooler months and falling to 6% in hot weather.

The errors resulted in frustration for GPs and anxiety for patients, with patients unnecessarily investigated and urgently referred for a repeat blood test. The researchers suggested GPs should review transport and phlebotomy arrangements if their practice's incidence of moderate hyperkalaemia was over 0.7%.

Study leader Dr Vanessa Thurlow, consultant clinical scientist at the Princess Royal University Hospital in Kent, said many spuriously high potassium tests resulted from samples have to travel long distances in cold conditions. ‘The longer a sample is exposed to the ambient temperature, the more likely there will be false results.'

Hospitals in North Bristol, Gloucestershire, West and South London and East Kent are currently reviewing their GP-commissioned pathology services and Dr Thurlow said GPs would not know about the changes before it is too late.

‘This kind of thing is happening slowly and insidiously over the country and GPs won't notice that it is happening suddenly and haven't been consulted. All these problems with the delays in sample transport and the distances patients have to go to get their blood taken have not been thrashed out in the planning process,' she said.

Dr Tom Frewin, a GP in Bristol who has worked in a pathology lab, said he was very worried about the effect of the proposed centralisation of pathology services in North Bristol. ‘It all depends on how soon the sample gets to the lab. Things will get worse because there is not joined up thinking. They need to start from the patient's arm and end with the GP consultation where they give the result,' he said.

The findings were published in a research letter in this month's British Journal of General Practice.

Blood test

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