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Fist clenches corrupt blood tests

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Patients should not clench their fists during phlebotomy procedures as it can cause high blood potassium readings, a UK study suggests.

Researchers from Kent calculated mean monthly serum potassium levels for 200,000 samples taken between 2002 and 2005.

Results were plotted before and after a change in practice at Bromley Hospitals NHS Trust, when senior nurses decided patients should not clench their fists. Incidence of high blood potassium fell significantly after the change.

‘Requesting patients to fist clench to ease venesection can lead to quantitatively serious overestimation of serum potassium,’ the authors said online in the Annals of Clinical Biochemistry.

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