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 final study published on this subject that I will discuss is more recent, although not that recent, having been done in 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. 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. Guidelines recommend blood samples from peripheral intravenous cannula be taken only on insertion. Anecdotal evidence suggests drawing blood from existing cannulas may be a common practice. Further research is required to resolve this issue. Keywords: acute care; adult nursing; diagnostic tests; haemolysis; peripheral venous catheterization; phlebotomy; systematic reviews and meta-analyses; venepuncture.
Abstract in English, Chinese. Publication types Meta-Analysis Systematic Review. Get a quote. Learn more about Routine Venipuncture online CE course. If the only vein available is proximal to above and near the IV, these steps should be followed: Ask the patient's caregiver if the IV can be turned off for a short period of time.
The IV should be discontinued for at least two minutes before the venipuncture. Apply the tourniquet between the IV site and the area of the venipuncture.
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