Top Ten Ways Blood Potassium Can Be Altered During and After the Draw
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. Recentrifugation — spinning gel tubes a second time has been found to increase the potassium level by 47%.
9. Inadequate centrifugation — 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 stoppers off — this technique has been shown to increase potassium levels in the specimen to be tested by 135 percent.
7. Pouring blood from one tube to 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, 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 pronounced can increase potassium levels up to 20%. That's enough to push a normal level into a panic range, 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.
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.
This Month in Phlebotomy Today
Here’s what subscribers to Phlebotomy Today, the Center for Phlebotomy Education’s paid-subscription newsletter currently in its 10th year of publication, are reading about this month:
For subscription rates and to subscribe to Phlebotomy Today, visit www.phlebotomy.com/PhlebotomyToday.html. The current month’s issue will be emailed to you immediately upon subscribing.
Featured FAQ: Discard tube
Q: There’s a lot of confusion at our facility about when we need to draw a discard tube. Can you clear this up for us?
A: The practice of withdrawing and discarding a portion of blood before filling a coag (blue-top) tube is old school. Truth be told, tissue thromboplastin, long thought to accumulate in the needle during the venipuncture, has never been proven to alter coag results. In fact, many studies have shown that if the citrate tube is the first tube drawn, protimes and aPTTs are not affected.
The recommendation for a discard tube was dropped in 1998 when the CLSI, the agency that establishes the standards for blood collection procedures, determined that there was insufficient evidence to support the practice. However, they still recommend it under two circumstances: 1) whenever specific factor assays are drawn such as Factor VIII; and 2) if you are drawing through a butterfly set. No studies have been attempted to determine whether or not tissue thromboplastin affects special factor assays. So CLSI suggests facilities establish their own protocol for such tests.
When using butterfly sets, you should apply a discard tube long enough to evacuate the air from the tubing so that the patient's tube filled isn't underfilled. It doesn’t have to be filled. Then apply the tube to be tested. Blue top tubes must be filled at least 90% of their volume in order for the coag studies to be accurate. There isn't much leeway.When employed, a discard tube can be another coag tube or a plain, non-additive tube.
Each month, PT-STAT! will publish one of the hundreds of phlebotomy FAQs in the growing database of questions and answers available in Phlebotomy Central, the members-only section of the Center for Phlebotomy Education's web site. For information on joining Phlebotomy Central, visit www.phlebotomy.com/PhlebotomyCentral.html.
Survey Says: Where Would You Seek Inpatient Services?
Our latest survey asked Phlebotomy Today STAT! readers: If given a choice, would you seek inpatient services at your employing institution for you or a loved one as opposed to elsewhere. Why?
Over 81% of those responding would have themselves or their loved ones treated at their facility. Eighteen percent would not. Some comments:
Overwhelmingly, survey participants expressed a vote of confidence in the quality of care their employing institutions provide. Recurring themes echoed among respondents who would seek medical care for themselves or their loved ones in-house were: 1.) the level of caring shown by the facility, 2.) the faith and trust they place in the employer and staff, and 3.) the high standards and level of care maintained. For the majority, the “insider knowledge” that comes with being an employee was a plus for the employer. For the 18% who would not seek inpatient services at their employing institution, find out where the other 81% work.
This month’s survey question: In your facility, is phlebotomy centralized ( i.e., phlebotomists perform all routine blood collections) or decentralized (e.g., staff of various disciplines are cross-trained to draw blood)? Click here to participate in the survey.
Featured Product: Blood Specimen Collection FAQs
What Would You Do?
Each month, What Would You Do? presents a different case study, then asks readers to contribute their ideas as to how each situation would best be handled. The following month, selected responses will be chosen by the editor and published (sender will be identified by first name and state only). The most accurate, well written response will receive a free download from the Center for Phlebotomy Education’s To the Point® library of articles. The exercise will conclude with a review of the selected submissions and a discussion of the standards pertinent to the case study.
Surprisingly, there were a wide variety of responses to this month's case study considering the risks of drawing above an IV and violating facility policy. Although the CLSI standards leave it up to the facility to establish a policy for drawing above active IVs, it clearly defines the perils. Testing for the same analytes being infused (e.g., sodium, potassium, glucose, etc.), adding orders for more tests on samples previously drawn above an IV are just two examples. While forty-two percent of those who responded said they'd draw above the IV at the nurse's request, only half of those said they'd document the circumstances; none indicated they'd make a notation on the sample itself, which is required by the CLSI standards in its last revision (2007) whenever drawing above or below an IV site.
Thirty-five percent said they would flat-out not draw the specimen because it's against facility policy regardless of pressure to do so. One respondent, a nurse and IV therapy manager, put it quite succinctly: "An individual nurse is not authorized to change policy." Fifty-seven percent indicated they would notify their supervisor or the physician before breaching the policy. (Total percentages exceed 100% due to some responses that fell into multiple categories.)
Bill from Ohio suggests having the physician order the blood to be drawn above the IV in writing to force a review of facility policy. In his words, "caution should be the key word, making sure that drawing from this site would not adversely affect the results of any testing."
Another reader, DeEtte of Michigan, shared a similar scenario that happened to her:
Seven percent said they'd draw from below the IV. The most surprising response came from the seven percent who said they'd draw from an artery. Surprising because arterial sticks as an alternative to venipunctures are a clear deviation from the CLSI standards. Not only do arterial punctures put the patient at increased risk of injury (and litigation since the standards so clearly advise against arterial draws as a venipuncture alternative), the composition of arterial blood is not equivalent to venous blood for many analytes.
We also liked the response from Elana, a nurse from Arizona:
"If it is NOT against hospital policy to draw from the IV, proper procedures may be taken to discontinue the infusion, flush with appropriate amount of saline, and draw off appropriate amount of 'waste' prior to drawing specimen, being sure to adhere strictly to hospital policy. If drawing from an infusion IV is prohibited, keep searching for veins, take actions like applying a warm compress, dangle the extremity... don't attempt the stick if you can't find a vein and seek assistance from a more expert phlebotomist."
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