The lifespan of blood components varies significantly. This question needs clarification, as it depends on what aspect of blood we're considering.
Red Blood Cell Lifespan
Normal human red blood cells, responsible for oxygen transport, have an average lifespan of about 120 days within the circulatory system. After this period, they are broken down and recycled by macrophages. This process is remarkably efficient, with macrophages removing roughly 5 million red blood cells every second. [Source: Reference mentioning 120-day lifespan of red blood cells]
HIV's Survival Time Outside the Body
In contrast to red blood cells, HIV's survival outside the human body is significantly shorter. While exact durations depend on environmental factors, studies indicate that HIV doesn't survive long outside its human host. In dried blood at room temperature, it may persist for up to six days, but its concentration diminishes considerably. Other sources mention HIV surviving for a few weeks under specific conditions. [Source: References discussing HIV's limited survival outside the body]
Blood Storage and Shelf Life
Stored blood, specifically red blood cell units, has a limited shelf life under controlled conditions. Guidelines exist for managing blood storage duration, with rules like the "30-minute rule" emphasizing that units exposed to uncontrolled temperatures for longer than 30 minutes are deemed unsafe for return to storage. [Source: Reference on the 30-minute rule for stored RBC units]
Conclusion
The "lifespan" of blood is context-dependent. Red blood cells circulate for approximately 120 days. HIV, on the other hand, has a significantly shorter survival time outside of the human body. The safe storage time of blood for transfusion also differs, depending on the component and storage conditions.
