How many people have heard of the 30 minute rule for units of returned blood? If you haven’t there is folklore that says once a unit of blood leaves the blood bank it is ok to return it to inventory if they get it back before 30 minutes are up. We even have a place on the documentation that accompanies the unit of blood to write down the time that we can accept a return. It was recommended to us that we get an infrared temperature meter so we could actually take the temperature of units when they are returned. One day I decided to play with my new toy and figure out how long a unit could really be out and still be ok to return. Our policy states a unit can be returned if the temperature is 10 degrees Celsius or colder.
I split my little experiment into two parts. Using an expired unit of blood, I left the unit on the counter and took the temperature every minute for 30 minutes. For the second part, I held an expired unit in my hand (simulating a nurse or transporter carrying the unit) and took the temperature every 2 minutes. In the first experiment the unit of blood reached 10°C in 19 minutes; at 30 minutes I recorded a temperature of 14°C. As expected, holding a unit in my hand sped up the rise in temperature; it took 12 minutes for the unit to reach 10°C. After 30 minutes the same unit was 17°C. In both experiments I mixed the blood before rolling the unit of blood around the thermometer.
This very informal experiment confirmed my suspicion that the temperature of a unit of blood is environment dependent. Put the unit in a warm room and it will warm up faster than if it were in a cold room. When we dispense units we place the unit in a thin plastic bag; the plastic on the blood units themselves is thin as well. There is no insulation from the unit and our warm hands.
So what do you do with this information? If you have a policy or use the 30 minute rule, I recommend suspending it immediately. There is no way of knowing what happens to that blood once it leaves your blood bank. If you do not have an infrared temperature meter, put it on the capital wish list for 2014. They will save you from taking back blood that is not safe and it will put a finite cut off point for taking units back. Once we started using the meter we found that the majority of blood that comes back is not suitable for reissue and ends up being disposed. While we do waste blood, I feel much better knowing that the blood that we do take back is suitable for transfusion and is ultimately better for the patient.
It is performing little experiments like the one outlines above that keeps us all interested in the laboratory field. What other career can you have a question about something, know how to figure out an experiment to find the answer, and then carry it out to see if you were right or not? Now the real question I have is: when I order the pizza for lab week what are the chances it gets here in 30 minutes or less?
–Tommy Transfusion is the pseudonym of a blood bank supervisor in the midwest.