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Is there a single irreversible indicator that works for both 6 and 10 degrees C?

It’s that time of year, so let’s talk turkey!

We get this question from blood banks a lot when helping them select and validate indicators. Our answer? No, there is not one irreversible indicator that works for two temperatures. Yet at the 2017 AABB Annual Meeting, we heard from a number of blood banks who said they are using ONE.

There are two problems with a “one size fits both” indicator: (1) the indicator is reversible up until it reaches endpoint and (2) the inability to validate the indicator.

Why Blood Banks Use Indicators

When blood is in the blood bank, under your control, you have a reasonable assurance that it is being maintained below the AABB guideline temperatures of 6oC for storage and 10oC for transport.  But when blood is out of your control, and then returned to the blood bank, an indicator is critical for confirming that it never exceeded the temperature endpoint. If the blood product reaches endpoint, an IRREVERSIBLE indicator gives you a visual cue – even if it has cooled down to an acceptable temperature by the time it arrives back in the blood bank.

Problem #1- Reversible indication up through 9oC

As noted, some blood banks are currently using a single product for both 6oC and 10oC requirements.  Let’s call it “Indicator A.” While it is true that this indicator gives you a real-time visual of the blood product temperature between 1oC to 9oC, indication is only irreversible at 10oC.

So, in the case of 10oC applications, if the endpoint “flower” hasn’t changed color when Indicator A arrives back to the blood bank, the blood is considered safe and can be returned to inventory.

This isn’t the case for 6oC applications, however, because the indicator does not provide irreversible indication until the blood reaches 10oC.  That means if the temperature of the blood rose above 6oC for a period of time, but still stayed below 10oC and then fell below 6oC before returning to the blood bank – there would be NO visual indication that exposure over 6oC had occurred.

The assumption that Indicator A is irreversible for BOTH 6oC and 10oC indication is false.  It is not.

Comparison of Temperature indicators: 6oC Irreversible Indicator vs. and 10oC Reversible Indicator

Problem #2 – Validation at 6oC

Validating a temperature indicator is an iterative process that involves measuring blood product temperature with a calibrated thermometer, and then recording the temperature at which the indicator reaches its irreversible visual indication state.

Indicator A can be accurately validated for 10oC applications, similar to our Safe-T-Vue 10.  Both will provide irreversible indication when the 10oC endpoint is reached – with Indicator A’s flower changing colors and Safe-T-Vue’s dot turning red.

If the intent is to use Indicator A for 6oC applications, however, it is impossible to validate it.  Indicator A provides no irreversible visual indication if the blood exceeded 6oC at any point during the time it was out of control of the blood bank.

Let’s Get Back to the Meat of It

Think about cooking a turkey. You set your oven to 450 degrees for 5 hours and wait for the plastic thermometer to pop to let you know the bird is done. You don’t care if the oven dipped to 350 when you opened the door to check it, you just care that your turkey is thoroughly cooked. The pop-up thermometer gives you an irreversible visual indication, but with no record of the actual temperature as it’s cooking.

The same applies to blood indicators:

  • A blood temperature indicator can provide irreversible indication of only one temperature, not two
  • There is no value in the “reversible” scale on an indicator; it doesn’t capture the temperature history – it only indicates real-time temperature
  • As a result, validation of a reversible indicator is impossible

This is why Temptime recommends using Safe-T-Vue 6 for 6oC applications and Safe-T-Vue 10 for 10oC applications.  Both are irreversible and can be validated for the indication temperature.

If you have questions about the difference between reversible and irreversible temperature indicators, and the importance of irreversible indicators, please contact us.  You can also read these validation procedures to get a better understanding of how a reversible indicator cannot be validated.  Or, request Safe-T-Vue samples and see for yourself.

Jeffrey Gutkind