Keeping Blood Products Cold During Dispensing

Tests show that gel blankets significantly help maintain temps below 6oC

Test Blood Bag Warming using reusable ice packsOn a recent visit to a blood bank customer who uses Safe-T-Vue 6, we learned something that we felt was worth sharing. During the approximate 10 minutes that it often took to do paperwork and cross-matching, they sometimes experienced the Safe-T-Vue 6 (STV-6) “tripping.” This caused concern that the blood product may have been compromised by room temperature exposure, even for a seemingly short time period.

To address this problem, they began using refrigerated gel blankets (reusable ice pack sheets) to keep the blood product cool. Taking this simple step of placing the blanket around the blood bag(s) during preparation and before transport to the ER/OR has given them confidence that the blood product has been kept cool, and the STV-6 provides visual indication and reassurance that 6°C has not been exceeded.

Wanting to learn just how much the gel blanket helped, we turned to Marielle Smith, Technical Service Scientist in our Temptime Lab, to do some testing. You may be surprised by what we learned.

Read this VUEPOINT to see the test procedure and learn from the detailed data we gathered. It may inspire you to try gel blankets in your blood bank!

Tests to compare blood bag warming with and without refrigerated gel blankets

When blood banks are preparing refrigerated blood bags for transport to the OR/ER, there is limited time for blood bank personnel to record the necessary patient information (cross-check, paperwork, etc.) before the blood approaches critical temperatures. Many blood banks use Safe-T-Vue 6 for exactly this reason.

Previous studies have shown that bags warm quickly to temperatures (6.0°C in less than 10 minutes) rendering the blood unsuitable for use. Results from this new study, however, demonstrate that using a refrigerated gel blanket (such as the Thermafreeze Reusable Ice Pack Sheet) makes a significant difference in slowing the warming rate when the blood product is removed from refrigeration to typical room temperature conditions.

Test procedure setup

A test was performed to assess whether using a refrigerated gel blanket can add to the longevity of the blood bags upon removal from refrigerated storage (1°C – 4°C).

The test was setup to collect temperature data as follows:

1. Control, single bag with no gel blanket
2. Single bag with small gel blanket, cutout window (to view Safe-T-Vue 6)
3. Three bags with larger gel blanket

Six (6) bags of 350 mL simulated red blood cells volume were used for scenarios 1 and 2, and 18 bags were used for scenario 3.

Reusable Ice Pack Sheets (e.g., gel blanket) were obtained and cut into different dimensions to allow for testing either a single bag (with a window cut-out to view the Safe-T-Vue 6 indicator) or 3 bags side-by-side.

Small gel blanket with viewing window for 1 bag

Large gel blanket for 3 bags

Temperature measurement

Calibrated temperature probes were inserted into each of the simulated blood bags. Calibrated electronic thermometers (accuracy of at least ±0.1°C) were used to record the temperature of the fluid inside the filled blood bags.

After pre-conditioning in the refrigerator (maintained between 1°C to 4°C) for at least 24 hours, the bags and the gel blankets were removed and placed lying flat on a counter-top at room temperature conditions (19°C ± 1°C with 50% R.H). A timer was set to count-up mode and temperature readings were recorded at one minute intervals until the temperature inside the bag reached 6°C.

Test results

The data points on the graph below show the gradual warming of the bags as the refrigerated blood bags warm to 6.0°C in room temperature conditions when the blood bag is either wrapped in a refrigerated gel blanket, or left as is upon removal from refrigerated storage (control).


  • Without using a gel blanket, blood bags warmed from 3.2°C to 6.0°C in approximately 9 minutes
  • Using a small gel blanket (with a window cut out to allow for visual interpretation of the Safe-T-Vue 6 indicator), blood bags warmed to 6.0°C in approximately 25 minutes
  • Using a large gel blanket for testing up to 3 bags side-by-side, blood bags warmed to 6.0°C in approximately 32 minutes

Conclusions and recommendations

The results presented in this report support that a pre-conditioned refrigerated gel blanket can be wrapped around blood products to keep the blood below 6°C for an extended period of time – while blood bank personnel are preparing the blood for transport to the ER/OR.

When a simulated blood bag was wrapped in a refrigerated gel blanket upon removal from refrigerated storage (1°C to 4°C), the bag warmed to 6.0°C within about 25 to 32 minutes on a counter at room temperature conditions. As an added precaution, a Safe-T-Vue 6 indicator can be used to provide irreversible visual indication of temperature excursions beyond 6.0°C.

Order free samples of Safe-T-Vue 6

Blood Bank Refrigerator Setpoints Matter

Learn about these important time/temperature correlations relative to your day-to-day blood bank operations.

Understanding the time pressures of busy blood banks, it would be fair to say that ANY time/temperature “advantages” – such as revisiting the refrigerator setpoint – might be worth consideration. Learn more in this VUEPOINT.

by Jeffrey Gutkind, Temptime

Over the past several months I’ve had the opportunity to visit some of the largest blood banks across the nation. In the course of talking with blood bankers about maintaining blood temperatures during storage, issue and transport, I observed a wide range of refrigeration setpoints, anywhere from 1.5oC to 4.7oC.

Reviewing my observations from these visits and reflecting on the AABB standard of 1.0oC to 6.0oC for storage, it brought me back to the “starting” temperature for blood when it’s removed from the refrigerator.

    • How does even a degree or two at a higher or lower storage temperature affect the blood temperature as it is dispensed and issued from the blood bank?
    • More importantly, how does the refrigerator setpoint affect how much TIME you have before the blood reaches 6oC?

To answer these questions, we asked Marielle Smith, Technical Service Scientist, to run a simple test in our lab.

How long does it take for refrigerated blood products to reach 6oC?

Blood Storage Temperature: 2°C vs. 4°C

The following table and graph show the time it takes for the core temperature of a refrigerated blood bag to warm to 6°C when removed from refrigerated conditions (2°C or 4°C) and placed on a counter-top at room temperature.1

The graph demonstrates that the lower the refrigerated storage temperature, the more time it takes for the blood bag to reach 6°C when warming at room temperature conditions. While these results are specific to the test method and setup used, they should be typical.

In terms of practical, day-to-day blood bank operations, what does this tell us?

Based on this test data, it suggests that blood bankers have over twice as much time to get blood issued and dispensed when the refrigerator setpoint is lower (2oC vs. 4oC). This represents a significant advantage for refrigerating blood at lower temperatures and longer times out of refrigeration before the blood goes out of specification.

Knowing that AABB guidelines state blood can be stored at 6oC for up to 42 days and transported between facilities below 10oC, and at the same time understanding the time pressures of busy blood banks, it would be fair to say that ANY time/temperature “advantages” such as revisiting the refrigerator setpoint might be worth consideration.

What do the blood refrigeration experts have to say?

After researching refrigerator setpoint specifications for a number of different vendors, we found that the factory setpoint is typically 4.0oC. Not being a refrigerator expert, I decided to reach out to Colleen Holtkamp Market Manager from Helmer® Scientific, to learn more. Colleen graciously provided these thorough answers to my questions, as well as thoughtful guidance for your consideration on setpoints, alarms and refrigerator specifications. (Colleen’s responses are in blue following the questions).

1. What is the typical factory setpoint temperature of your refrigerators when they go into the field? Are these setpoints easily changed, or does it have to be reset by the factory?

“The typical setpoint for Blood Bank Refrigerators is 4oC. Per AABB Standards, the acceptable temperature for storage of whole blood and most red cell components is 1oC to 6oC. Setting the temperature to 4ºC, close to the middle of the range, is standard practice for blood bank refrigeration.

It should be noted that the alarm setpoints are important, as well. AABB Standards state that alarms should be set to activate before blood components are exposed to unacceptable conditions. For example, since the lower limit for blood storage is 1oC, it makes sense to set the low alarm to 1.5oC (and since the upper limit is 6oC, a high alarm setting of 5.5oC is appropriate).

The ability to change the temperature setpoint depends on the manufacturer/brand of the refrigerator, as does the process for changing the alarm settings (instructions should be included in the refrigerator’s user manual).

Helmer Scientific Blood Bank Refrigerators enable the operating setpoint and alarm settings to be changed at the facility (they do not have to be reset by the factory). With temperature and alarm settings, it’s important to remember that while it should be reasonably convenient to modify them, it shouldn’t be so easy that they tend to be changed by mistake. A safeguard such as password protection for the refrigerator settings offers the best of both worlds – security and ease of use.”

2. Is there some type of statistic that you would use to say if the door is open for 3 minutes per hour; it will take XX minutes to get back down to the original setpoint?
As an example: If the refrigerator is set to 3.0oC and the door is open for 2 minutes, how long will it take for the refrigerator to get back down to the 3.0oC setpoint?

“There isn’t a standard method for measuring temperature recovery after a door opening. It can be impacted by variables such as ambient temperature and how much cold product is stored in the refrigerator at the time. What is important is that the unit has a heavy-duty, forced air refrigeration system and that the fan stops running while the door is open so that it does not blow out the cold air. In addition, the refrigeration system should be powerful enough to circulate the air inside the cabinet multiple times shortly after the door is closed, ensuring quick temperature recovery.

Another consideration is the importance of alarms. Having both a door open alarm and a high temperature alarm provides two layers of protection against temperature excursions due to door openings.”

3. What is the typical tolerance for blood bank refrigerators? (we found this information difficult to find in our online research).

“Blood Bank requires the tightest temperature uniformity of any cold storage application. The typical temperature uniformity specification for Blood Bank Refrigerators is +/-1oC. While not necessarily a regulatory requirement, many Blood Banks have written this specification into their internal protocols/SOPs. Therefore, it has become a community standard that drives performance expectations for Blood Bank Refrigerators.

Before a Blood Bank considers changing refrigerator setpoints from 4oC to 2oC, it is critical to think about the following information. If a blood refrigerator is set to 2oC, with uniformity of +/-1oC, the temperature inside the unit might reach the lower limit of the acceptable range (1oC). Also, if the low alarm is set to 1.5oC (which is advisable because AABB standards state that alarms should activate before blood is exposed to unacceptable conditions), it may be triggered by operation at 2oC. Helmer Scientific’s priority is to optimize the temperature of the blood bag while it is stored in our units. The setpoints and alarms are established to protect the blood while it is in the refrigerator.”

When it comes to blood bank refrigeration setpoints, what have we learned?

• The typical factory setpoint for blood bank refrigerators when delivered from the manufacturer is 4.0oC
• The ability to change the refrigerator setpoint at the blood bank varies by manufacturer
• Blood that is stored at 2oC takes over twice as long (approximate, based on our test) to reach 6oC at ambient, when compared to blood stored at 4oC
• Temperature recovery of refrigerators is affected by a number of variables (door opening, amount of stored cold product, ambient operating temperature)
• Low and high alarms, as well as open door alarms, are important and recommended by the manufacturers

If you have any recommendations, experiences, questions or ideas relative to refrigerator storage temperatures and your blood bank, we’d love to hear from you. Please POST A COMMENT or email us.

Jeffrey Gutkind

1Test Details
At each storage temperature, a total of six (6) simulated blood bags were tested. Each 600mL PVC blood bag (Charter Medical) was filled with 350mL of a mixture of 10% glycerol and 90% water, to simulate red blood cell volume. The bags were removed from refrigerated storage (at 2°C and 4°C) and then placed lying flat on a counter-top at room temperature (at approximately 21°C with 30% R.H). The temperature was measured by placing a calibrated temperature-sensing probe in the center of the simulated blood mixture inside the bag and the temperature was monitored using a calibrated Oakton Thermistor Thermometer. Temperature readings were recorded at 1 minute intervals. The data represents the time needed for the simulated blood mixture (10% glycerol with 90% water) to warm to 6°C.

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