Phlebotomy Top Gun: Drawing Blood from a Patient Receiving Intravenous Fluids [Hot Topic]

Brad Karon, M.D., Ph.D.

Drawing blood from a patient’s arm with intravenous infusion running has the potential risk for erroneous and misleading laboratory test results.  CLSI guidelines recommend using the opposite arm whenever possible. Dr. Karon discusses 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.

Presenter and Credentials:
Brad Karon, M.D., Ph.D., Consultant in the Division of Clinical Core Laboratory Services  and Associate Professor of Laboratory Medicine and Pathology in the College of Medicine at Mayo Clinic in Rochester, Minnesota.


Our speaker for this program is Dr. Brad Karon, a Consultant in the Division of Clinical Core Laboratory Services at Mayo Clinic in Rochester, Minnesota. Dr. Karon is also Associate Professor of Laboratory Medicine and Pathology in the College of Medicine.Welcome to Mayo Medical Laboratories Hot Topics. These presentations provide short discussion of current topics and may be helpful to you in your practice. Today our topic is Phlebotomy Top Gun: Drawing Blood from a Patient Receiving Intravenous Fluids.

Thank you, Cara.  For those of you who have not attended our phlebotomy conference here in Rochester, the title of my hot topic today, “Phlebotomy Top Gun,” may seem a little odd, but I hope I’ll be able to explain to you what is “Phlebotomy Top Gun” and what we try to do at our annual phlebotomy conference.

I have no disclosures relevant to today’s presentation.

Every year at phlebotomy conference, I present a talk that’s always 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 related 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—“In a patient with an IV catheter, you may draw from the same arm that has the IV catheter if...

  • The first answer or choice for the audience would be—You may only draw above the IV.
  • The second choice would be—You can draw below the IV with a tourniquet between the IV site and the draw site.
  • The third choice would be—You can only draw from the opposite arm.
  • And the fourth choice would be—The available data suggest that the second and third options are equally appropriate.

And 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.

So, again, this is a case that I presented at a previous phlebotomy conference; and what I do next with each case in the “Phlebotomy Top Gun” presentation is go through any data, evidence, either internal or external to the Mayo Clinic practice that exist and then re-poll at the end to see if anybody’s mind has been changed; and, finally, at the end I’ll give you what I feel is the correct answer to this question I asked.  Regarding drawing in patients with IV catheters, the CLSI guidelines specifically address this issue so we’ll start by reviewing the current CLSI guidelines.  The applicable guideline, CLSI GP41-A6, is also called “Procedures for the Collection of Diagnostic Blood Specimens by Venipuncture.” 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.  The guidelines also mention or refer to 2 primary studies that looked at the impact of drawing blood below an IV catheter as opposed to or vs drawing from the other arm.

CLSI guidelines go on to give recommendations about techniques for drawing below (distal to) an IV catheter, recommending that the IV catheter be turned off for 2 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.

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 and below the IV site, and from the opposite arm, while the IV catheter was running.  The IV fluids were then shut off for 2 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 2-minute pause in IV fluids also seemed to work fairly well.

The other study cited in the CLSI guidelines is also older, 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 site (even with a tourniquet in place) as opposed to drawn from the other arm.

Within our practice at Mayo, we have an IT system used in our central and stat clinical 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.  And if the results obtained 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 2 minutes, even when 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 is running through a venous catheter.  Pausing the IV fluid is necessary to obtain accurate glucose concentrations in patients with intravenous fluids being administered.

Intravenous replacement of calcium, magnesium, and phosphorus is 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 replacement protocols at our institution recommend that calcium, magnesium, and phosphorus levels be drawn no sooner than 2 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 intravenous infusion has been finished, the specimens are not truly contaminated, in that the blood concentration measured at this time may be analytically accurate, but does not reflect the 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 IV catheter with a tourniquet or from the opposite arm--is less important than timing for measuring calcium, magnesium, and phosphorus in patients receiving intravenous replacement of these electrolytes.

At this point during the phlebotomy conference, I would return to the original question that I polled the audience on.  The attendees of the conference would use the audience response system to respond again, and I would share with the audience what I believe the correct or intended response to be.  Based upon available data and our collective experience here at Mayo, my opinion is 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 2-minute pause of IV fluids is highly desirable to avoid contamination regardless of which site is chosen.

Thank you for your time and attention today.  If you liked today’s presentation, or even if you didn’t, please consider attending the upcoming Mayo Medical Laboratories phlebotomy conference: “Phlebotomy 2015: Meeting the Challenges of a Changing Health Care System.” As in previous years, the conference will feature presentations from expert speakers covering a variety of topics in phlebotomy skills, phlebotomy management and other topics.  Learning will take place via both large group didactic sessions, and small group break-out sessions that allow more interaction with conference speakers.  Tours of Mayo Clinic facilities will also be offered during the conference, and this year we will also have a blood drive as part of the lab week celebration going on the week of the conference.  I will also be presenting an all new “Phlebotomy Top Gun” presentation, addressing questions and issues submitted by attendees during the registration process for the conference.  Thank you for listening today and have a wonderful day.


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