Blood’s stability outside the body varies significantly depending on conditions and what aspect of its “lasting” is considered, such as remaining liquid, maintaining cellular viability, or retaining infectious agents. The environment blood is exposed to fundamentally alters its composition and potential.
Factors Influencing Blood’s Stability
Temperature plays a substantial role, with higher temperatures accelerating the degradation of blood components and lower temperatures promoting preservation. For instance, cold temperatures can extend the activity of HIV in a syringe for several days or even weeks. Humidity also influences blood’s drying rate; in high humidity, blood may remain moist longer, while low humidity causes it to dry more quickly.
The type of surface blood lands on also impacts its stability. Porous surfaces like fabric may absorb blood, leading to faster drying and potentially trapping components within fibers. Non-porous surfaces, such as glass or metal, allow blood to pool and dry more slowly, potentially concentrating components as it dries. Exposure to air and oxygen causes blood to undergo oxidation, a process where the iron in hemoglobin reacts, changing the blood’s color from red to brown or even black as it dries. This “rusting” process signifies the breakdown of hemoglobin.
Light exposure, particularly ultraviolet (UV) radiation, can degrade blood components. UV light can damage the viral envelope of HIV, quickly inactivating the virus. Overall, these environmental influences combine to determine the rate at which blood cells, proteins, and genetic material break down.
Blood’s Lifespan in Different Forms
When blood is exposed to air, such as in a fresh spill, it typically begins to clot within minutes. This natural process forms a solid mass, and the remaining liquid portion eventually dries.
Dried blood can persist on surfaces for extended periods, and certain components within it remain stable. Genomic DNA in dried blood spots can be stable for at least 11 years when stored on filter paper in ambient tropical conditions. Even at room temperature, DNA in dried blood can remain stable for up to a month. Pathogens, however, have varying survival rates; for example, HIV can be detected in dried blood for several days, though its infectivity significantly decreases within hours of air exposure.
In medical settings, blood is carefully stored under controlled conditions to extend its viability for transfusions. Packed red blood cells are typically stored at 2-6°C and can remain viable for up to 42 days, depending on the preservative solutions used. Platelets require storage at a controlled room temperature of 20-24°C with continuous agitation and have a shorter shelf life of 5-7 days. Fresh frozen plasma is stored at temperatures below -18°C and can be kept for up to a year, or even longer at colder temperatures. These specialized storage methods maintain the functionality of blood components for therapeutic use.
Health and Safety Considerations
Exposure to blood outside the body carries potential health risks due to disease transmission. Viruses like Hepatitis B (HBV) and Hepatitis C (HCV) can survive outside the body for considerable periods. HBV can remain infectious on surfaces for at least 7 days, even in dried blood. HCV can survive and remain infectious on environmental surfaces at room temperature for up to 6 weeks. In contrast, HIV is fragile outside the body, with 90-99% of the virus becoming inactive within hours of air exposure, though it can persist for several days under specific conditions, particularly in syringes.
General safety advice for handling blood spills involves universal precautions, treating all blood as potentially infectious. This includes wearing disposable gloves and, if splashing is possible, eye protection and a mask. Spills should be absorbed with disposable towels, and the area should then be cleaned with a hospital-grade disinfectant, such as a 1:10 bleach solution. All contaminated materials, including gloves and towels, should be placed in biohazard bags for proper disposal. Prompt and thorough cleanup helps minimize the risk of exposure to bloodborne pathogens.