Properly storing blood samples is fundamental to the diagnostic process, directly impacting the reliability of test results. Meticulous storage practices preserve sample integrity by stabilizing components like hormones, enzymes, or metabolites. If not maintained correctly, these analytes can degrade, leading to inaccurate measurements and misleading clinical interpretations. Careful maintenance prevents pre-analytical errors, which account for a large percentage of laboratory mistakes.
Immediate Handling and Sample Preparation
Immediate handling requires using the correct collection tube, which contains specific additives tailored to the test. Tubes with anticoagulants like EDTA or Heparin are used for whole blood, while plain tubes allow clotting for serum separation. After collection, tubes with additives must be gently inverted to ensure full mixing. Vigorous shaking must be avoided, as it causes hemolysis—the rupture of red blood cells—which releases intracellular components that skew results.
For many tests, cellular components must be separated from the liquid portion (serum or plasma) through centrifugation. This spinning process should occur promptly, ideally within two hours of collection, to prevent ongoing metabolic activity from altering analyte concentrations. Accurate, legible labeling is critical to maintain the chain of custody. Every tube requires a minimum of two unique identifiers, typically the patient’s full name and medical record number, along with the date and time of collection.
The Role of Temperature in Sample Preservation
Temperature is the most important factor in blood sample preservation, as it dictates the rate of chemical and biological changes. For short-term holding of certain whole blood samples, such as those for routine hematology, ambient temperature (15°C to 30°C) may be acceptable for a few hours. However, most plasma and serum samples require a cooler environment to slow enzymatic degradation. Refrigerated storage, typically 2°C to 8°C, is common for samples analyzed within a few days and is suitable for many chemistry and immunology tests. A laboratory-grade refrigerator must be used to ensure consistent temperature control.
For long-term storage or highly sensitive analytes, samples must be frozen at significantly colder temperatures, such as -20°C, -70°C, or -80°C. These deep-freeze temperatures effectively halt most enzymatic activity, preserving the sample for months or years. Samples destined for long-term banking should be transferred into specialized cryovials and stored in a consistent, monitored environment. Placing samples in a standard refrigerator freezer compartment should be avoided, as it does not reach the necessary ultra-low temperatures and can damage whole blood cells. Preventing a single freeze-thaw cycle is crucial to avoid degradation.
Understanding Sample Stability and Time Limits
Sample stability is the time period during which an analyte’s concentration remains within an acceptable range of its true value. This duration varies widely based on the specific test and storage temperature. Blood gas samples, for example, are highly time-sensitive and require immediate analysis because cellular respiration continues to alter gas concentrations. Glucose also degrades rapidly in unseparated whole blood due to glycolysis.
To stabilize glucose, a specific collection tube containing sodium fluoride is required, or the plasma must be separated from the cells quickly. Other sensitive markers, such as parathyroid hormone and homocysteine, begin to change within hours, necessitating prompt processing even if refrigerated. While many common chemistry analytes remain stable for up to 24 hours in unseparated blood at room temperature, this is not a universal rule. Even under ideal frozen conditions, some analytes, including lipids and hormones, can show measurable degradation over several years.
Safe Packaging and Transit to the Laboratory
The final phase involves packaging the specimen for safe transit to the testing facility, prioritizing temperature maintenance and preventing leaks. Samples should first be placed into a primary, leak-proof container, such as a sealed tube. They are then secured within a durable, secondary containment vessel, often a plastic bag with absorbent material. Requisition forms must accompany the package but should be kept separate from the biological material to prevent damage if a leak occurs.
For transit, the entire package must be placed in an insulated cooler or box designed to maintain the required temperature conditions. For refrigerated samples, frozen gel packs are used to keep the temperature between 2°C and 8°C throughout the journey. If the sample must remain frozen, dry ice is typically required, necessitating specialized packaging and shipping procedures due to its classification as a hazardous material. Users of at-home collection kits must follow specific shipping instructions precisely, often including a designated overnight courier service.