What is “stop temperature?”

Return to Refrigerator Challenge” generates new questions from blood banks

This was the most common question we received from blood bankers in an unprecedented response to our January 2017 VUEPOINT.  In that issue of VUEPOINT, we shared the results of a “Return to Refrigerator Challenge” – where a major university hospital conducted a test to compare two blood temperature indicators.  Their intention was to evaluate indicator performance when unused blood was returned to the blood bank.

Although this was the first time we discussed stop temperature in a VUEPOINT, it’s not the first time we’ve received questions about it from our blood bank contacts. To address those issues, we researched what stop temperature means for indicator manufacturers who use this specification. We found that stop temperature appears to relate to the chemical indication behavior.  This means that if the blood product temperature is below the stop temperature, the indicator does not change color.

How does a 10oC indicator with an 8oC stop temperature behave?

The 10oC indicator used in the challenge has a specified stop temperature of 8oC.  If the blood product begins to exceed the stop temperature (8oC), the 10oC indicator’s chemical indication material melts back to its liquid state. This melting reaction gives users a visual indication that the blood product is no longer in compliance. This type of indicator may signal that the blood product is out of compliance once it exceeds 8oC, even if it never reaches 10oC, as shown in this example.

What does this mean to blood banks using a stop temperature type indicator?

Now that we understand what stop temperature is, the question is what does the specification – and indicator performance – mean to blood banks?  Specifically, what happens if the blood product is hovering around the 8oC stop temperature for any period?

Tests shared by blood banks, combined with our studies, have shown that under a wide range of exposures and times – once the indicator exceeds its stop temperature of 8oC, the indicator may be irreversibly tripped.  In multiple tests, the blood product temperature was being internally monitored to confirm that it remained below the indication temperature of 10oC before being returned to the blood bank refrigerator.  After the blood bags were returned to the refrigerator for reissue, many indicators had tripped during the refrigeration period.

Comments and questions from blood banks based on findings

  • “Doesn’t this make it an 8oC indicator?”
  • “We have many bags that are returned to the blood bank at 8oC and they look OK. We put them in the refrigerator and they show overheated.  This is an 8oC indicator.  We are throwing out good blood.”
  • “This did not show up in the standard validation, and it never occurred to us to try this while performing the validation. After performing the ‘return to refrigerator challenge’ we found that the indicator just did not perform”.

We are grateful for comments and questions like these because they help fuel our blood indicator knowledge and testing.  Clearly, the “stop temperature” specification may be new to many blood banks and is something to be further explored.  Please share your experiences and observations so we can continue learning together.