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At the heart of general practice since 1960

GPs urged to shake up lab testing procedure

By Nigel Praities

GPs may be faced with huge numbers of inaccurate blood test results as a result of plans to centralise a number of pathology services around the country, say researchers.

Their audit of all GP-requested potassium results in Bromley, South London, over a four-year period showed that nearly one in five were false positives at certain times of the year. But the authors predicted the problem could get worse as hospitals look to consolidate their pathology services and samples have to travel longer distances.

They found an average of 9% of potassium results were too high, rising to 17% in the cooler months and decreasing to 6% in hot weather.

These result in much frustration for GPs and anxiety for patients, as patients have to be unnecessarily investigated for risk factors and urgently referred for a repeat blood test.

Dr Vanessa Thurlow, lead author and consultant clinical scientist at the Princess Royal University Hospital in Kent, said many spuriously high potassium tests were due to patients being asked to clench their fists when blood is taken, or because samples have to travel long distances in warm conditions.

‘The longer a sample is exposed to the ambient temperature, the more likely there will be for false results,' she said.

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 distance 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 on lab results.

‘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 audit data was published in a letter in this month's edition of the British Journal of General Practice.

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