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Top Ten Ways Phlebotomists Change Potassium Results

Inaccurate potassium results can't be fixed, only prevented.

by Dennis Ernst • October 08, 2021

Technical


Few components of the blood are as vulnerable to blood collection, handling, and processing (preanalytical) technique as potassium is. In fact, Young's Effects of Preanalytical Variables on Clinical Laboratory Tests lists over 50 preventable preanalytical conditions that cause a potassium level to be falsely elevated. 

Do you contribute to inaccurate potassium results when you draw, transport, handle, or process blood samples? Critique yourself with this list of common errors that can lead patients with normal potassium levels to appear elevated, and patients with dangerously low levels to appear normal:

10. Centrifuging the sample twice---spinning gel tubes a second time has been found to increase the potassium level by 47%.

9. Centrifuging samples improperly---without enough g-force, platelets can remain in the serum. Because platelets release potassium, they can contribute to the concentration in the serum to be tested, presenting an erroneous impression to the physician of the patient's physiology.

8. Spinning tubes with the stoppers off---this technique has been shown to increases potassium levels in the specimen to be tested by 135 percent.

7. Pouring blood from one tube into another---pouring contents from an EDTA tube into a tube to be tested for a profile that includes potassium is like spiking it with pure potassium. Okay, that's an exaggeration, but still. It's a really, really bad idea.

6. Delayed centrifugation---red cells, which have 25 times as much potassium as the serum or plasma they're swimming in, will leak K+ once they leave the body. Within two hours, the serum/plasma in the tube is significantly higher in the electrolyte than what's really in the patient.

5. Chilling tubes before centrifugation---the mechanism that keeps potassium inside the red cells slows to a crawl at chilled temps. Refrigeration is for vegetables and fish, not blood that will be tested for potassium unless the serum or plasma has been separated from contact with the cells.

4. Hemolysis---red cells are rich in potassium. When they rupture because of poor collection or handling techniques, it adds to the total concentration in the serum or plasma to be tested and reported.

3. Incorrect order of draw---when filling EDTA tubes before filling tubes to be tested for K+, enough blood can carry over by the needle that pierces the stopper to spike the potassium to grossly distorted levels.

2. IV contamination---many IVs infuse potassium. When drawing from a vascular-access device or above a temporarily discontinued IV, you risk contaminating the sample with enough residual K+ to confuse the physician.

1. Fist pumping---having your patient pump his/her fist to make veins more pronounce can increase potassium levels up to 50%. That's enough to push a normal level into a critical value that demands immediate action, or spike life-threateningly low potassiums into a normal range. Fist pumping in patients has been reported to be responsible for one third of all elevated potassiums, and half of those that require immediate physician notification. If fist pumping is necessary to find a vein, release the tourniquet for two minutes before performing the puncture to allow blood in the arm to return to its basal state.

Consider potassium to be your problem child that insists on running wild. Controlling its behavior takes discipline and a consistent application of the rules of blood sample collection and processing. Take a time out and make sure these top ten threats to accurate potassium results don't cause your patients' potassiums to run amok.

For a detailed PDF to help you investigate questionable potassium results, consider our SmartChart™ "Investigating Elevated Potassium Results. 

For a full-length video detailing the multitude of ways potassium results can be altered during collection or processing leading physicians to question results, consider our video Potassium Results Your Physicians Can Trust.


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centrifugation EDTA order of draw potassium preanalytical pseudohyperkalemia

2 Comments

Phlebotomist

Very crucial subject!

I was looking forward to see a document about fist pumping as I saw many phlebotomist do it or do not stop patients from doing it yet it affect life threatening.

Thank you so much for meaningful informative educative email.

Best Regards,

Hafidha

Hafidha Bouzido, 10/08/2021 16:40:12

Fist Pumping

Yes!!! I constantly am telling my patients do not fist pump due to false information for bloodwork!

Kylee Pedersen, 10/13/2021 13:36:18


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