The Trouble with Infrared Thermometers
Infrared thermometers are used in many blood banks as the sole means for recording blood product temperatures when blood is returned for storage. There are several problems that affect infrared thermometers and impede technicians’ abilities to make a determination whether a blood product should be discarded or not.
Studies have shown that a blood product’s surface temperature can be several degrees higher than its true core temperature¹. Although this may seem like a small difference, this temperature delta can potentially result in a large number of “false-positive” wastage events. By monitoring core temperature, a blood product can be exposed to room temperature almost 4x longer than if surface temperature is used to trigger wastage. Given that each unit of wasted blood may cost over $30⁰², switching to core temperature monitoring could represent a significant cost savings opportunity.
When a blood product is sent to an OR there are many unpredictable factors that can contribite to how and when a product exceeds its regulated temperature guidelines. Often times blood products are left outside of their coolers in ambient conditions for extended periods of time. When measuring the temperature of blood products it is very important to have an accurate picture of what the product went through once it left the blood bank. When a product is returned to the blood bank and the technician reads the temperature, they are only seeing one split second of that product’s temperature profile.
The accuracy of the handheld IR thermometer is primarily determined by the distance-to-spot ratio (D/S Ratio). This ratio is the size of the area being evaluated by the IR thermometer as it relates to distance. In other words, the area being measured becomes larger as the distance increases. The smaller the target, the closer you should be to it. This ratio will have a significant impact on the accuracy or precision of the reading.
Most IR thermometers have accuracy specifications that range from +/- 1.0 ºC to +/- 2 ºC and their distance specifications range from 1 to 2 meters. These specifications might come as a surprise to many blood bank technicians. The variables that affect the accuracy of the temperature readings made by an infrared thermometer can often times complicate a task that should be fairly simple.