Phlebotomy Tips: Why You Shouldn’t Pump Your Fist Before a Blood Draw

Are you a phlebotomist, or interested in learning more about phlebotomy? If so, you’ve come to the right place. Getlabs Phlebotomy Tips is a series focused on sharing knowledge, advice, and best practices for phlebotomists and mobile phlebotomists.

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How often do patients sit down for a blood draw and immediately start pumping their fist the moment you apply the tourniquet? If you’re a phlebotomist or medical professional that draws blood, then you know it happens a lot.

We know the patients are just trying to help. If anything, they think they’re making their veins easier to find - and it just might. However, pumping your fist before a blood draw can have a serious effect on the accuracy of lab results. Especially when it comes to potassium levels.

Here’s why you shouldn’t allow patients to pump their fists before a blood draw and alternatives to help minimize the likelihood of misdiagnosing a patient with inaccurate potassium results.

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Why you shouldn’t pump your fist before a blood draw

According to the leading guide to possible causes of abnormal test results, the Effects of Preanalytical Variables on Clinical Laboratory Tests, there are over 80 preanalytical variables that can cause potassium levels to be falsely elevated. And when you start to look at the reasons behind these variables, there is one that stands out as one of the biggest and most common: fist pumping.

That’s right, fist pumping before a blood draw is one of the most common reasons for potassium levels to be falsely elevated.

In fact, one study found that fist pumping increases potassium levels up to 2.7 mEq/L. It has also been reported that patients pumping their firsts prior to a blood draw causes a third of all elevated potassium results. Even more so, it’s also responsible for half of all critical-value potassium results.

What many patients don’t realize is that pumping their fist can inadvertently double the concentration of potassium in the sample of blood. And when that happens, the physician gets potassium results that no longer represent what’s really going on with the patient.

For example, if the patient comes in with a normal potassium level, but they’re allowed to pump their fist, it can lead the laboratory to report wildly elevated potassium levels. The physician might treat the patient for a condition they don’t have.

Alternatively, a patient might come in with a really low potassium level, but the phlebotomist allows them to pump their first. The laboratory might then report a normal potassium level for the patient and not provide treatment for a condition they have.

This can lead to under-medication, overmedication, misdiagnosed, undiagnosed, or mismanaged care. That’s why it’s so important phlebotomists prevent patients from pumping their fists in the first place.

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Alternatives to fist pumping during a blood draw

Despite how widespread it’s been reported that pumping your fist elevates potassium levels, many medical professionals still permit it - or even request it.

That’s why it’s a good idea to train patients to not pump their fists and educate them around why it’s not a good idea. This way, if they encounter a medical professional who is not aware of the negative effects of pumping the fist, at least the patient will know to avoid the practice.

Instead, instruct your patients to clinch and hold their fists - but only if necessary. Pumping should never be attempted no matter how difficult the vein is to locate.

As an alternative, veins can be made more obvious by warming the site with a warm compress, or by lowering the patient’s arm. If pumping the fist is the last resort, release the tourniquet for two minutes to allow blood in the arm to return to its basal state.

If you can eradicate one most commonly committed clinical error and ensure that no patient has their blood drawn after pumping their fists, your patients are going to be treated according to more accurate potassium results. No one is going to be overmedicated, undermedicated, or undiagnosed because you understood the effects of fist pumping on test results.

As always, thanks for stopping by! We look forward to sharing more phlebotomy tips and best practices with you in the future.

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