The question of whether blood can “go bad” is complex, depending on its state: circulating within the body, stored for medical use, or collected for laboratory analysis. While blood in a healthy individual continuously renews, blood removed from the body has a finite lifespan, undergoing changes that limit its utility. Understanding these distinctions is important for grasping blood’s properties and its handling.
Blood Within the Body
Blood circulating within a healthy body does not “go bad” like food. The body continuously produces and recycles blood components, preventing degradation and maintaining its ability to transport oxygen, nutrients, and waste products effectively.
Red blood cells, responsible for oxygen transport, have a lifespan of approximately 115 to 120 days. As they age, they undergo membrane changes and are eventually removed from circulation by organs like the spleen and liver. New red blood cells are constantly generated in the bone marrow, replacing older ones at a rate of millions per second.
Stored Blood: Why It Has a Shelf Life
Blood collected for transfusions has a limited shelf life due to changes occurring outside the body. Red blood cells, the most commonly transfused component, are typically stored for up to 42 days at 2–6°C in a preservative solution. Platelets, another important component for clotting, have a much shorter shelf life, usually 5 to 7 days, and require continuous agitation at room temperature (20–24°C). Fresh frozen plasma (FFP) can be stored for up to a year at or below -25°C.
The primary reason donated blood “goes bad” is “storage lesion.” This involves structural, metabolic, and morphological changes of the red blood cells during cold storage. Metabolic impairment occurs as glucose and other necessary substrates become depleted, while metabolic waste products like lactic acid accumulate. This leads to a reduced pH and impairs enzymes involved in energy production and antioxidant defense, affecting the red blood cells’ ability to deliver oxygen efficiently.
Additionally, red blood cells can become less deformable, meaning they lose flexibility and struggle to navigate small capillaries, impacting oxygen delivery. Oxidative damage also plays a role, with reactive oxygen species accumulating and damaging cellular components. These changes, along with the degradation of coagulation factors and potential bacterial contamination, require strict expiration dates to ensure the safety and efficacy of blood products. Anticoagulants like citrate, along with additive solutions like adenine, glucose, and mannitol, are added to donor blood to prevent clotting and extend its viability by supporting red blood cell metabolism and maintaining pH.
Blood Samples: Integrity Over Time
Blood collected for diagnostic testing, research, or forensic analysis also changes over time, affecting integrity and accuracy. While these samples do not “spoil” in the traditional sense, their analytical value degrades. Factors such as temperature, agitation, and exposure to light can compromise sample quality.
Cellular components within a blood sample can begin to break down, a process called cell lysis, releasing intracellular contents and altering biochemical measurements. Enzyme activity continues, potentially degrading specific compounds, and bacterial contamination can occur, further skewing results. Certain analytes, like glucose, can decrease as cells continue to metabolize it, while potassium levels may increase due to red blood cell breakdown.
For diagnostic purposes, the timing of analysis is important. For example, comprehensive metabolic panel (CMP) results may become unreliable after 12 hours, even when refrigerated, while some complete blood count (CBC) parameters remain stable for up to 24 hours at room temperature, or up to 3 days with refrigeration. DNA in blood samples can remain stable for up to a month at room temperature, but live blood cells lose viability within two days without specialized preservation. Proper handling, including immediate testing, appropriate refrigeration or freezing, and the use of specific additives, is necessary to maintain the integrity of blood samples for accurate results.