Platelets are tiny cell fragments in the blood that play a fundamental role in stopping bleeding and maintaining blood vessel integrity. They are a crucial part of hemostasis, the body’s natural response to injury.
The Role of Platelets
The primary function of platelets is to initiate clotting, forming a plug to seal damaged blood vessels. When injured, platelets activate and adhere to the site, changing shape and releasing chemical signals that attract more platelets. This rapid accumulation forms a temporary platelet plug, staunching blood flow.
Platelet Lifespan in the Body
Platelets have a relatively short lifespan within the circulatory system, typically 8 to 12 days. They originate in the bone marrow, produced by large cells called megakaryocytes. These megakaryocytes extend long cytoplasmic protrusions, known as proplatelets, which then fragment into thousands of individual platelets.
Once released into the bloodstream, platelets circulate. Their production is regulated by a hormone called thrombopoietin. As platelets age or become damaged, they are naturally removed from circulation, primarily by specialized cells in the spleen and liver. This continuous cycle maintains a stable platelet count in the blood.
Platelet Lifespan in Storage
Donated platelets, crucial for transfusions, have a restricted lifespan when stored outside the body, viable for only 5 to 7 days from collection. This limited shelf life stems from specific storage requirements designed to maintain their function and minimize risks. Platelets must be stored at room temperature (20-24°C / 68-75°F) and require continuous gentle agitation. This agitation ensures proper gas exchange, preventing a drop in pH and maintaining platelet viability.
The strict storage conditions are essential because platelets are susceptible to changes that can impair their effectiveness. A primary concern is bacterial contamination, as room temperature provides an ideal environment for bacterial growth. Over time, platelets also undergo metabolic changes and lose their functional capacity, a process referred to as platelet storage lesion. Regulatory bodies, such as the FDA in the U.S., stipulate a 5-day shelf life for platelets, which can be extended to 7 days if specific bacterial detection methods or pathogen reduction technologies are employed. This precision in storage is crucial for patient safety and the therapeutic efficacy of transfused platelets.
Factors Influencing Platelet Lifespan
Numerous factors can influence the lifespan and viability of platelets, both within the body and during storage. In the human body, certain medical conditions can shorten platelet lifespan or impair their function. Autoimmune disorders, such as immune thrombocytopenia, can cause the immune system to mistakenly destroy platelets. Infections, including bacterial or viral infections like HIV and hepatitis C, can also lead to decreased platelet survival.
Some medications, such as certain chemotherapy drugs, anticoagulants like heparin, or even common pain relievers like NSAIDs, can reduce platelet production or affect their function and lifespan. Nutritional deficiencies, particularly of vitamins like B12 and folate, can similarly impact platelet production. In stored platelet units, factors like the method of collection (e.g., apheresis versus whole blood derived) and processing techniques can influence their quality. Adherence to proper storage conditions, including precise temperature control and constant agitation, is essential, as deviations can lead to reduced viability and a shorter shelf life for these components.