Expires: May 7, 2024
Brad Karon, M.D., Ph.D., is Co-Director of Laboratory Services for the Department of Laboratory Medicine and Pathology at Mayo Clinic in Rochester, Minnesota. He is also a Professor of Laboratory Medicine and Pathology.
Contact us: MMLHotTopics@mayo.edu.
Hi, I’m Bobbi Pritt, Director of the Clinical Parasitology Lab and Vice Chair of Education in the Department of Laboratory Medicine and Pathology at Mayo Clinic. Did you know that drawing blood from a patient’s arm with intravenous infusion running has the potential risk for erroneous and misleading laboratory test results? In this month’s “Hot Topic,” Dr. Brad Karon will discuss what laboratory test results are adversely affected when drawing from an arm with an IV running and what the phlebotomist can do to minimize these errors. I hope you enjoy this month’s Hot Topic, and I want to personally thank you for allowing Mayo Clinic the opportunity to be a partner in your patients’ health care.
Thank you for the introduction. For those of you who have not attended our phlebotomy conference here in Rochester, the title of my topic today, “Phlebotomy Top Gun,” may seem a little odd, but I hope I’ll be able to explain to you what “Phlebotomy Top Gun” is and what we try to do at our annual phlebotomy conference.
I have no disclosures relevant to today’s presentation.
Every year at the Mayo Medical Laboratories phlebotomy conference, I present a talk that’s called “Phlebotomy Top Gun.” The format of “Phlebotomy Top Gun” is a case-based presentation. I solicit from you, the Attendees, cases, issues, or questions that you like to hear about. I present these as case-based scenarios, and using an audience-response voting mechanism, the attendees of the conference vote on the action or answer they feel is appropriate to the case. I then present the collective experience from our practice and the evidence and data that I can find relevant to the topic. At the end of the case, the attendees vote again. For each case, I can see whether I’ve been able to change anyone’s mind on the question at issue by presenting the data and information relevant to the topic. This is an actual case from a “Phlebotomy Top Gun” presentation at a previous phlebotomy conference in Rochester. In this case, the question was:
Q: In a patient with an IV catheter, you may draw from the same arm that has the IV catheter if . . .
At this point, during the live conference, attendees using an audience-response system would vote for the answer they thought was most appropriate, and we would get to see in real-time the distribution of results that our audience felt was correct.
Cases often start with a review of relevant Clinical and Laboratory Standards Institute (CLSI) guidelines. In this case, the applicable CLSI guideline is CLSI GP41-Edition 7, also called “Collection of Diagnostic Venous Blood Specimens.” The guidelines note that there is risk of obtaining erroneous and misleading results when drawing blood from a patient with an IV catheter. The guidelines recommend using the opposite arm (not the arm with the IV catheter) whenever possible, and when not possible, collecting the specimen below (distal to) the IV site.
CLSI guidelines go on to give recommendations about techniques for drawing below (distal to) an IV catheter, recommending that the IV be turned off for two minutes or longer and that a tourniquet be placed between the IV site and the blood draw site. Finally, the guidelines mention that collection above (proximal) to the IV catheter is not recommended and should be done only when all other options for blood collection have been exhausted. Getting back to the question in this case, to find an answer we should further investigate the data in the studies that were mentioned or referred to in the CLSI guidelines and data from other studies or relevant Mayo Clinic experience.
The first study I want to discuss was published some time ago, in 1983. These investigators measured a complete blood count and various chemical parameters in 18 healthy individuals who did not have an IV in place or running. A peripheral IV was then started, and fluids were allowed to infuse for 30 minutes. Samples were then drawn from above the IV site, below the IV site, and from the opposite arm while the IV catheter was running. The IV fluids were then shut off for two minutes, and samples were drawn a third time from the IV catheter site. A number of hematological and chemical parameters were different from the baseline values when the specimen was drawn from above the IV catheter while fluids were running. Glucose and phosphate were different from baseline when they were drawn either below the IV site or from the opposite arm, keeping in mind that for this experiment the IV fluids were not turned off for these collections. When the IV was not turned off, there were no differences in glucose or phosphorus collected below the IV versus in the other arm. Drawing from the IV site after a two- minute pause in IV fluids also seemed to work fairly well.
Another study on this subject, even older, was performed in 1979. Using a similar design, the investigators compared chemical and hematological parameters in individuals with a peripheral IV running, by either using a tourniquet between the IV site and draw site and drawing below the IV, or drawing from the other arm. Again, in this experiment, the below-IV site and other arm were compared while the IV fluid was running. For the complete blood count and 18 chemical parameters analyzed, only glucose values showed any difference between the below-the-IV draw site and a draw from the opposite arm. The glucose concentration was quite a bit higher, by 43 mg/dL, when it was drawn from below the IV (even with a tourniquet in place) as opposed to drawn from the other arm.
The final study published on this subject that I will discuss is more recent, although not that recent, having been done in 1988. In this study, 24 healthy volunteers had solutions of 5% dextrose in normal saline infused through an IV for 20 minutes. The IV was stopped and samples were collected above (proximal to) the IV site and from the other arm at 1, 2, and 3 minutes after the IV solution was stopped. Values for sodium, chloride, red blood cell count, and glucose were compared between arms at 1, 2, and 3 minutes after stopping the IV solution; the values were also compared to baseline values obtained before the IV solution was infused. Values for sodium, chloride, and red cell count were close to baseline values, whether collected above the IV or from the other arm, by around one minute after stopping the IV solution. In contrast, glucose values in the arm with the IV were much higher than the opposite arm. Glucose values began to come back down to baseline values by 2 to 3 minutes after the IV was stopped, though values remained around 5 to 10 mg/dL higher in the arm with the IV compared to the opposite arm. These authors concluded that the dilutional effect of collecting proximal to or above an IV, even when the solution is stopped for only 1 minute, is fairly minimal. However, if a substance being infused (glucose in this case) is going to be measured, then a 2- to 3-minute pause is necessary to achieve accurate values. These particular authors recommended a 3-minute pause, and the data are really the source of the recommendation for a 2- to 3-minute pause in IV fluids before blood draw.
Within our practice at Mayo, we have an IT system used in our central and stat laboratories that allows us to detect patterns of results that likely represent contamination with IV fluid. In these cases, we most often initiate a redraw for these specimens. If results with a redraw specimen are different from the original results, we confirm that specimen contamination did in fact occur on the first draw. Therefore, in our practice, we have over time obtained a large database of types of contaminated specimens. In our practice, we find that falsely elevated glucose concentrations represent one of the most common contamination scenarios for patients with venous catheters. We have collected dozens (if not hundreds) of instances where glucose concentrations were falsely elevated when intravenous fluids were not paused for at least two minutes, even if we document that specimens were drawn from the opposite arm that contained the IV. Both existing evidence and our experience suggest that contamination is worse when drawing from below the IV site rather than the opposite arm, but that neither procedure (drawing below the IV with a tourniquet or drawing from the opposite arm) is a reliable way to measure glucose when an intravenous infusion that contains glucose is currently running. Pausing the IV fluid is necessary to obtain accurate glucose concentrations in patients with intravenous fluids being administered that do contain glucose.
Intravenous replacement of calcium, magnesium, and phosphorus is also very common among acutely or critically ill patients. Contamination of specimens among patients receiving intravenous calcium, magnesium, or phosphorus replacement is a special case that merits a brief discussion. Calcium, phosphorus, and magnesium undergo redistribution between the vascular space and the cellular compartments. Reaching equilibrium for these electrolytes likely takes an hour or more, rather than just 2 or 3 minutes. The electrolyte replacements protocols at our institution recommend that calcium, magnesium, and phosphorus levels be drawn no sooner than two hours after the termination of an intravenous infusion of any of these electrolytes, in order to avoid false elevations. While there is a false elevation that results from drawing the calcium, magnesium, or phosphorus levels too soon after an IV infusion has been finished, these specimens are not truly contaminated, in that the blood concentration measured at this time is analytically accurate, but it does not reflect the true value that will be observed once cellular equilibrium has been reached. Although there is not a lot of data published on this issue, it is likely that site of draw—that is below the IV catheter with a tourniquet or from the opposite arm—is less important than timing of the blood draw for calcium, magnesium, and phosphorus relative to when intravenous infusions are stopped.
At this point during the phlebotomy conference, I would return to the original question on which I polled the audience. The attendees of the conference would use the audience-response system to respond again, and I would share with the audience what I believe to be the correct or intended response. Based upon available data and our collective experience here at Mayo, in my opinion, the single best answer to this question would be option 4. The available data suggest that collection below the IV with the tourniquet, and from the opposite arm as the IV, are equally effective approaches to collecting blood from a patient with an IV. Although not explicitly asked or stated in this question, a minimum two-minute pause of IV fluids is highly desirable and perhaps more important than the choice of site in terms of avoiding contamination.
Thank you for your time and attention today. If you liked today’s presentation, or even if you didn’t, please consider attending a future Mayo Medical Laboratories phlebotomy conference. We hold the conference in the spring each year, and learning takes place via both large group didactic sessions and small breakout sessions that allow more interactions with conference speakers. Tours of Mayo Clinic facilities are also offered during the conference. Thank you for listening and have a wonderful day.