When blood leaves the body and enters a syringe, its stability becomes a significant concern. Understanding how long blood remains viable in this environment is important for various applications, ranging from diagnostic testing to medical research. Blood’s intricate biological composition means it changes immediately upon collection, impacting its integrity for analysis or use. This understanding helps establish practical guidelines for handling and storage.
Immediate Changes to Blood
Once blood is drawn into a syringe, intrinsic biological processes begin. The coagulation cascade activates rapidly, leading to clotting within minutes if no anticoagulant is present. For instance, blood without an anticoagulant can coagulate in as little as 11 seconds and solidify within two minutes. This clotting process involves platelets and plasma proteins forming a mesh-like structure.
Beyond clotting, blood cells undergo changes. Red blood cells can experience hemolysis, where their membranes rupture and release hemoglobin into the surrounding fluid, which can interfere with certain tests. Additionally, the metabolic activity of blood cells continues, consuming nutrients like glucose and producing waste products, altering the sample’s chemical composition over time.
External Factors Affecting Stability
External factors significantly influence blood degradation within a syringe. Temperature plays a primary role; colder temperatures slow metabolic processes and preserve sample integrity. Blood samples kept at refrigerator temperatures, typically between 2°C and 8°C (35.6°F to 46.4°F), maintain stability for longer than those stored at room temperature.
Anticoagulants are another crucial factor. Anticoagulants like EDTA, heparin, or citrate prevent blood from clotting, which is often necessary for specific diagnostic tests. Different anticoagulants preserve blood components for varying durations; for example, blood in an EDTA tube can remain stable for a complete blood count (CBC) for up to 24 hours. Air exposure can also contribute to changes in the sample through gas exchange and oxidation, further affecting stability.
Risks of Prolonged Storage
Prolonged storage of blood in a syringe introduces several hazards. One significant risk is bacterial contamination, as blood provides a rich growth medium. Injecting old blood, even if it appears visually unchanged, can lead to serious infections like septicemia.
Prolonged storage also compromises the integrity of analytes, substances measured in diagnostic tests. This degradation can lead to inaccurate test results, affecting patient diagnoses and treatment decisions. For instance, certain comprehensive metabolic panel (CMP) parameters can become unreliable after just 12 hours of storage at 4°C. Loss of cellular viability also makes blood unsuitable for medical applications, such as transfusions or certain research studies requiring living cells.
Standard Handling Guidelines
To ensure sample integrity and accurate results, standard guidelines emphasize prompt processing. For most diagnostic tests, blood should be processed rapidly, often within minutes to a few hours of collection. This involves transferring blood from the syringe into appropriate collection tubes, which may contain additives or anticoagulants, then processing it further, such as by centrifugation to separate plasma or serum.
Specific guidelines vary depending on the intended test. For instance, while complete blood count (CBC) parameters can be stable for up to 24 hours at room temperature, comprehensive metabolic panel (CMP) tests require processing within 12 hours for reliable results, especially when refrigerated. Blood collected for serum separation can be stored at 4–8°C for up to 24 hours before serum is separated, but it must not be frozen as whole blood. Generally, keeping blood in a syringe for extended durations without proper anticoagulants and temperature control is not recommended due to the rapid onset of degradation and the risks involved.