Reducing the incidence of pseudohyperkalemia by avoiding making a fist during phlebotomy: A quality improvement report

Background: Pseudohyperkalemia is uncommon, but important. Local release of potassium caused by contraction of the forearm muscles from a tightly clenched fist or repeated fist clenching during phlebotomy is a recognized cause of pseudohyperkalemia. We investigated the use of a standard protocol to avoid fist clenching during phlebotomy. Study Design Quality improvement report. Setting & Participants In 7 healthy volunteers, 10 blood samples were collected over 10-second intervals after 20 repeated fist clenching and unclenching movements. In 86 healthy volunteers, 3 blood samples were collected with and without prior fist clenching. Between September 1, 2006, and June 30, 2007, peripheral venous blood samples were collected from 73,846 outpatients at Chiba University Hospital without a protocol to avoid fist clenching. Between July 1, 2007, and March 31, 2009, blood samples were collected from 171,053 outpatients using the protocol. Quality Improvement Plan After July 1, 2007, blood samples were collected from the basilic or cephalic vein without making a fist or by making a fist using minimal gripping strength. Also, when multiple specimens were obtained from 1 patient, the specimen for measuring serum electrolytes was obtained after the other specimens. Outcomes & Measurements Pseudohyperkalemia, defined as unexplained serum potassium level <6.5 mmol/L. Results In the 7 volunteers, the decrease in serum potassium levels after cessation of fist clenching ranged from 8.4%-25.9%. In the 86 volunteers, the percentage with a decrease in serum potassium level <0.2 mmol/L between the first and third samples was 25.6% versus 6.7% with or without prior fist clenching, respectively. In clinical practice, we observed 8 cases of pseudohyperkalemia before implementing the protocol (0.0081%) and 1 case (0.00058%) after implementing the protocol (P = 0.001). Limitations Causes of hyperkalemia before using precautions were assessed using retrospective analyses. Conclusions Avoiding fist clenching during phlebotomy and not using the first specimen for electrolyte measurements when obtaining multiple specimens from a single patient can reduce the occurrence of pseudohyperkalemia.