Whether blood must be refrigerated has a complex answer that depends entirely on its intended use and the duration of storage. Blood is a living, complex biological material, and its viability begins to degrade immediately upon leaving the body. Improper handling can quickly render the blood useless for transfusion or compromise the accuracy of laboratory test results. The strict temperature control protocols used in medicine are designed to slow down biological processes for clinical use.
The Biological Necessity of Temperature Control
Blood cannot be stored at room temperature for extended periods because the red blood cells remain metabolically active, even outside the body. These cells continue to consume their internal energy stores, primarily adenosine triphosphate (ATP). ATP is necessary to maintain their flexible shape and membrane integrity. As ATP is depleted, the red blood cells become stiff and lose their ability to efficiently carry oxygen.
This metabolic stress ultimately leads to cellular damage, a process known as hemolysis, where the red blood cells rupture and spill their contents. The release of free hemoglobin and other cellular components makes the blood product toxic and ineffective for a recipient. Warmer temperatures also provide an ideal environment for bacteria to multiply rapidly, creating a severe risk of life-threatening infection.
Storage Requirements for Transfusion Blood
Blood intended for life-saving transfusions is subject to stringent temperature regulations to preserve its full therapeutic potential. Stored Red Blood Cells (RBCs) and Whole Blood must be maintained within a narrow temperature range, typically between 1°C and 6°C. This cold storage dramatically slows the metabolic rate of the cells, conserving energy reserves and delaying hemolysis.
Specialized anticoagulant and preservation solutions, such as CPDA-1 or AS-1, are added to the blood upon collection. These solutions prevent clotting and provide necessary nutrients, extending the maximum shelf life of refrigerated RBCs to 42 days. Blood bank refrigerators are continuously monitored. Any temperature excursion outside the 1°C to 6°C range triggers an alarm and requires immediate investigation. Units that exceed 10°C must often be discarded because the risk of bacterial proliferation is too high.
The storage requirements for other blood components differ significantly from those for red cells. Platelets must be stored at a much warmer temperature, between 20°C and 24°C, and require continuous gentle agitation to prevent clumping. Conversely, Fresh Frozen Plasma (FFP), which contains clotting factors, must be stored at ultra-cold temperatures, typically at or below -18°C. These component-specific requirements underscore that the precise temperature is dictated by the biological properties of the component being preserved.
Handling Diagnostic Blood Samples
The temperature requirements for small blood samples drawn for laboratory testing are varied and depend on the specific analysis being performed. Most chemistry tests require the blood to be separated into serum or plasma quickly, usually within two hours. This prevents the blood cells from altering the composition of the fluid. Once separated, the serum or plasma can often be refrigerated (2°C to 8°C) for several days before analysis.
Some tests require immediate chilling to prevent the breakdown of the substance being measured. For example, blood drawn to measure ammonia levels must be placed on ice immediately. This slows down the in vitro generation of ammonia by cellular enzymes. If a sample is delayed or not chilled, the resulting ammonia measurement may be falsely high.
Conversely, chilling can interfere with the accuracy of other common tests, such as potassium levels. When whole blood is refrigerated, the red blood cell membrane’s sodium-potassium pump slows down. This causes potassium to leak out of the cells and into the surrounding fluid. This refrigeration-induced leakage creates a falsely elevated potassium result, known as pseudohyperkalemia. Unseparated whole blood samples for potassium are often best kept at room temperature until they can be processed.