Phlebotomy & Potassium Levels

Doctors and clinicians question potassium levels more than any other blood component level. Hemolysis tops the list of reasons for questionable readings. Achieving accurate potassium level measures is subject to many variables, including how phlebotomists draw blood. Bailey and Thurlow's 2008 paper published by the Annals of Clinical Biochemistry demonstrates that phlebotomy professionals still ask patients to "make a fist," even though this action sometimes dramatically raises potassium level readings.

Importance of Potassium Levels

• High potassium levels suggest heart or kidney disease. Normal potassium levels for adults range from 3.5 to 5.3 mEq/L. Low potassium levels suggest diabetes or occurrence of trauma. Blood potassium readings can be altered during the blood draw or how it is transported and later analyzed. In addition to improper fist-clenching, when phlebotomists use iodine to prep the draw site or canulas treated with benzalkonium, or draw shallow capillary blood, inaccurate potassium levels may result.

Improper Potassium Level Readings

• According to Donald S. Young's Effects of Preanalytical Variables on Clinical Laboratory Tests, 3rd ed., 2007, 50 plus entirely preventable circumstances improperly increase lab potassium level readings. Some common errors occur when blood meets centrifuge. When the centrifuge's spinning or g-force does not work well, blood platelets do not separate from blood serum. Because platelets hold potassium, an erroneous high serum concentration warrants physician investigation. Spinning the tubes twice increases potassium levels. Spinning tubes after removing their caps also increases potassium levels. Any delays in centrifuging the blood specimen also create problems. When the sample rests as little as two hours, potassium leaks from red blood cells. The serum level rises dramatically and creates incorrect elevated readings of potassium.

Hemolysis, Order of Draw and Contamination

• Hemolysis occurs when red blood cells rupture. Anything from blood collection technique to its transport to the lab sets the stage for hemolysis. The blood serum's concentration of potassium increases when red cells release their potassium load. Order of draw creates false potassium level readings. If the phlebotomist fills EDTA or venous blood collection tubes before filling profile testing tubes, potassium levels increase. Drawing blood from a central venous catheter or vascular access device or from an area above an IV site, especially when infusing potassium, creates false high readings

Misconceptions

• By now, all phlebotomists should know that asking patients to pump their fists is poor practice. The action prior to taking blood increases the potential for high potassium levels due to intracellular potassium leaks to blood serum. If your lab technician asks you to clench and unclench a fist prior to a blood draw, bring Bailey and Thurlow's 2008 study to her attention. If high potassium levels present after such an event, your doctor may request a second test.

Best Practice

• According to Bailey and Turlow, patients should close the hand at blood draw needle insertion. The hand should remain relaxed before and during blood collection.