Blood samples are a fundamental tool in healthcare, providing crucial insights into a person’s health status. They enable medical professionals to diagnose illnesses, monitor treatments, and assess overall well-being. The information derived from blood tests guides many clinical decisions, making sample integrity important for accurate medical assessments.
Key Factors Influencing Sample Stability
The viability of a blood sample for accurate testing is influenced by several conditions. Time is a significant factor, as biological samples naturally degrade over time due to metabolic processes. Temperature plays an important role, with extreme heat or cold potentially damaging cellular components and chemical substances within the blood. For instance, exposure to high temperatures can cause red blood cells to rupture, a process known as hemolysis, which can alter test results.
Anticoagulants and other additives in collection tubes are also important for preserving sample integrity. These chemicals prevent the blood from clotting or help maintain the stability of specific components required for certain tests. For example, EDTA (ethylenediaminetetraacetic acid) binds to calcium ions, preventing clotting and preserving blood cell morphology for tests like a complete blood count. Sodium fluoride is used in glucose testing tubes to inhibit glycolysis, the breakdown of glucose by blood cells, thereby helping to maintain accurate glucose levels.
Proper handling and processing techniques are equally important for sample stability. This includes gentle mixing of the sample with additives, timely centrifugation to separate plasma or serum from blood cells, and appropriate storage conditions. Delays in processing can lead to degradation of sensitive analytes, impacting the accuracy of results. Maintaining consistent temperatures during transport and storage is also important to prevent degradation and ensure reliable test outcomes.
Typical Lifespans for Common Tests
The lifespan of a blood sample varies depending on the specific diagnostic test and storage conditions. For a Complete Blood Count (CBC), which analyzes different blood cell types, samples are generally stable for up to 48 hours when refrigerated at 4°C, though some parameters may show changes after 8 hours at room temperature.
For a Basic Metabolic Panel (BMP) or Comprehensive Metabolic Panel (CMP), the stability of individual components differs significantly. Glucose, for example, is particularly sensitive and can decrease by 5-7% per hour in whole blood if not processed promptly. To ensure accurate glucose readings, samples are ideally analyzed within 1-2 hours or collected in tubes containing glycolysis inhibitors like sodium fluoride. Electrolytes and kidney function markers, however, are typically more stable and can remain viable for several days when refrigerated.
Coagulation tests, such as Prothrombin Time (PT/INR) and Activated Partial Thromboplastin Time (APTT), are time-sensitive. Plasma samples for PT and INR tests are generally stable for up to 24 hours when refrigerated, and up to 36 hours if frozen. APTT samples, however, are less stable and may deteriorate within 12 hours even when refrigerated. A lipid panel, which measures cholesterol and triglycerides, typically remains stable for several days when samples are refrigerated.
What Happens When Samples Degrade
When blood samples degrade, the accuracy of laboratory test results can be compromised. Degradation can lead to falsely high or low readings for various analytes, which can directly affect a diagnosis. For instance, hemolysis, the breakdown of red blood cells, can release intracellular components like potassium and lactate dehydrogenase into the plasma, leading to artificially elevated levels. Conversely, hemolysis can cause a decrease in values for other analytes, such as glucose and sodium.
Inaccurate results stemming from degraded samples can have serious consequences, potentially leading to misdiagnosis or delayed treatment for patients. A clinician relying on compromised data might initiate an incorrect treatment plan or miss a developing health issue. To prevent such errors, laboratories often have strict criteria for sample acceptance and may reject samples that show signs of degradation or improper handling.
Common reasons for sample rejection include clotting, hemolysis, insufficient sample volume, incorrect tube types, or improper labeling. When a sample is rejected, it necessitates a redraw, causing inconvenience for the patient and delaying crucial test results. This can prolong the diagnostic process and impact timely medical care.
Differences for Donated Blood
Blood collected for donation has different storage and lifespan requirements compared to samples used for diagnostic testing. Donated whole blood is typically separated into its components: red blood cells, plasma, and platelets, each with specific storage conditions and shelf lives to maximize their utility for transfusion.
Red blood cells are stored in specialized refrigerators at temperatures between 2°C and 6°C and can be preserved for up to 42 days with preservative solutions. In specific circumstances, red cells can be frozen below -65°C using cryoprotectants like glycerol, allowing for storage up to 10 years. Platelets, which are important for clotting, require storage at a controlled room temperature, usually between 20°C and 24°C, with continuous gentle agitation to prevent clumping and maintain functionality. Their shelf life is considerably shorter, typically around 5 to 7 days from collection.
Plasma is rapidly frozen at temperatures below -30°C to preserve clotting factors and plasma proteins. Fresh frozen plasma must be frozen within 8 hours of collection and can be stored for up to one year.