Validating Temperature Indicators: The “Return to Refrigerator” Challenge

Learn more in this VUEPOINT about indicator comparison tests we conducted based on reports from blood banks experiencing indicators “tripping” after returning blood products to the refrigerator

by Jeffrey Gutkind, Temptime

We are often called on by blood banks to answer questions about temperature indicators and support their validation requirements.  They also interface with us when they are having “issues” with an indicator, whether it’s Safe-T-Vue or a competing product, and are looking for insight and possible solutions.

Temperature indicators “tripping” after return to refrigerator

Several times over the past year we’ve interacted with blood banks experiencing a specific temperature indicator problem.  Here’s how it goes – the unused blood is returned to the blood bank and the indicator shows that it is still in compliance, that it hasn’t exceeded its 10oC indication temperature.   Great!  So, the blood is returned to the blood bank refrigerator for future reissue.

Then, at a later time, the when the blood is removed from the refrigerator for reissue –the indicator has “tripped” or turned color.  How could this be?  If the temperature was in compliance going IN to the refrigerator, how could it then be out of compliance AFTER being refrigerated?

The “Return to Refrigerator Challenge”

Blood Temperature Indicator Comparison

Figure 1: “Return to Refrigerator Challenge” Temperature Indicator Test Setup

In response to this influx of concern from blood banks, we decided to conduct a comparison test.  Fortunately, we had an opportunity to work with a major university medical center to gather validation data focused specifically on the “return to refrigerator” portion of the blood product’s journey. We refer to this test as the “Return to Refrigerator Challenge.”

The purpose of the challenge was to simulate a typical blood product journey – blood being issued to another department, such as the OR, and removed from the cooler for a brief period of time, and then returned to the blood bank.   A temperature probe would be placed in the blood bag, and the performance of two types of 10oC indicators would be compared.

  1. A probe was inserted into a (simulated glycerol-water) blood bag, which was placed in the refrigerator until it reached 4.2oC.
  1. The bag was removed from the refrigerator. Five Safe-T-Vue 10 indicators and five ‘Indicator A’ were affixed to the blood bag. (Figure 1)
  1. The blood temperature was allowed to reach 8.5oC. The indicators were observed and observations recorded (Figure 2).
  1. The blood bag was placed back in the refrigerator at 4.2oC (to simulate blood being returned to the blood bank for reissue) for 30 minutes.
  1. After 30 minutes, the blood bag was removed from the refrigerator. The indicators were observed and observations recorded (see Figure 2).

Figure 2: “Return to Refrigerator Challenge” Indicator Pass and Fail Data

*Note: Accuracy of Safe-T-Vue 10 is +/- 0.4oC and published accuracy of Indicator A is +/- 0.5oC

Challenge proves need to validate indicator performance throughout journey

Comparing the performance of the two indicators (Figure 2), it was apparent that the Safe-T-Vue indicator had accurately performed as expected and within the specifications.   Two of five ‘Indicator A’ had prematurely indicated (at 8.5oC) prior to refrigeration, and all five had failed to perform to specification after refrigeration at 4.2oC for 30 minutes.

Based on the manufacturer’s published accuracy specifications, Safe-T-Vue performed successfully, whereas ‘Indicator A’ failed to perform to specification.  Not only did 2 out of 5 ‘Indicator As’ “trip” at 8.5oC, all five of the indicators had tripped within 30 minutes of being refrigerated at 4.2oC.   This may be due to Indicator A’s published “stop temperature” of 8.0oC.

Is it necessary for you to conduct your own “challenge?”

This “return to refrigerator challenge” proved that the Safe-T-Vue indicator could be validated for returning blood products to the blood bank. If you have confidence in the performance (to specification) of the indicators you are using, then you probably don’t need to conduct your own “challenge.”  But, if you’ve had issues like we described early in this VUEPOINT, where indicators are mysteriously changing while under refrigeration, you may want to conduct the “challenge” to be certain that the indicators are performing as specified.

Validate critical points in your process to confirm indicator performance

The typical, standard validation should help you identify indicators that do not perform to specification (for example the two Indicator A’s that tripped at 8.5oC, which does not meet the published specification of +/- 0.5oC).   The closer look of the “challenge” could be used to confirm additional failure to perform to specification, particularly in situations where the indicator performance seems odd or questionable.

As always, we welcome your feedback on this topic.  And if we can provide validation support or help you address any temperature indicator issues, please contact me.

Jeffrey Gutkind

Leave a Reply

Your email address will not be published. Required fields are marked *