Blood preservation for scientific and medical applications involves maintaining the integrity and quality of blood samples from the moment of collection until analysis. This process is paramount because the reliability of diagnostic test results, research success, and medical assessment accuracy depend on the sample’s condition. Improper preservation can lead to degradation, rendering the sample unsuitable and potentially compromising patient care.
Understanding Blood Collection Tubes
Blood is collected into specialized vials, blood collection tubes, distinguished by stopper color. These colors signify the specific additives contained within, designed to preserve blood components for specific analytical goals. The type of additive dictates whether the blood will clot to yield serum or remain in a liquid state for plasma or whole blood analysis.
Anticoagulants are substances that prevent blood from clotting. Ethylenediaminetetraacetic acid (EDTA), found in lavender or purple-top tubes, works by binding to calcium ions, necessary for clotting. This action preserves cellular components, making EDTA tubes suitable for complete blood counts (CBC) and blood typing. Heparin, present in green-top tubes, inhibits thrombin, a clotting protein, and is used for chemistry tests. Sodium citrate, found in light blue-top tubes, also binds calcium ions, but its effect is reversible, making it suitable for coagulation studies where calcium can be added back for analysis.
Conversely, some tubes contain clot activators to promote rapid clotting for obtaining serum. Serum Separator Tubes (SSTs), with gold or mottled red and grey stoppers, contain silica particles that accelerate clotting and a gel that separates clotted blood cells from serum after centrifugation. This separation provides a clear serum sample for chemistry, immunology, and serology tests. Choosing the correct tube is the foundational step in ensuring the sample is prepared for its intended analysis.
Immediate Steps After Collection
Once blood is drawn into the collection tube, immediate handling is necessary to maintain its integrity. For tubes containing anticoagulants or clot activators, gentle mixing is important to ensure the additive is thoroughly dispersed throughout the blood. This is achieved by inverting the tube gently 8 to 10 times, rather than shaking vigorously.
Vigorous shaking can cause hemolysis, the rupture of red blood cells. Hemolysis can alter test results, leading to inaccurate diagnoses. Therefore, a smooth, controlled inversion motion is important to prevent mechanical stress on the blood cells.
Proper labeling of the collected sample is another immediate and important step. Each tube must be clearly labeled with patient identifiers (e.g., full name, date of birth, medical record number), along with the date and time of collection. This practice ensures accurate identification and traceability, preventing misidentification errors that could compromise patient safety and test reliability.
Optimizing Blood Sample Storage
Maintaining blood sample integrity over time requires specific environmental conditions, particularly regarding temperature. Short-term storage typically involves refrigeration at temperatures between 2°C and 8°C. Whole blood samples can generally be stored under these refrigerated conditions for up to 72 hours without significant degradation, which is suitable for many routine tests.
For longer-term preservation, freezing is necessary, with temperatures ranging from -20°C to -80°C, or lower, like -196°C in liquid nitrogen. Different components of blood have varying stability. When freezing, it is important to use appropriate cryovials to prevent contamination and maintain sample integrity.
An important consideration in frozen storage is avoiding repeated freeze-thaw cycles. Each cycle can cause ice crystal formation and osmotic stress, damaging cellular structures and degrading analytes, compromising the sample’s quality and leading to unreliable test results. To mitigate this, samples intended for multiple analyses should be aliquoted, or divided into smaller portions, before initial freezing. Additionally, proper sealing of vials is important to prevent evaporation and contamination during storage, regardless of the temperature.
Ensuring Sample Integrity
Even with proper collection and storage, several factors can compromise a blood sample’s quality. Hemolysis can occur due to factors like improper needle size or difficult venipuncture. Hemolysis can interfere with many laboratory tests by releasing intracellular substances like potassium and enzymes, leading to inaccurate results.
Bacterial contamination can also degrade the sample. Microorganisms can metabolize analytes, altering their concentrations and rendering the sample unsuitable for analysis. Additionally, certain analytes within the blood sample can degrade over time due to their inherent instability or enzymatic activity if not properly inhibited by additives. For instance, some analytes are only stable for a short period, such as 12 hours at 4°C, while others can remain stable for several days.
To counteract these issues, timely processing and analysis of blood samples are important. Quality control measures, including visual inspection for signs of hemolysis or clotting before testing, help ensure that only high-quality samples are analyzed. Adhering to these practices, from initial collection through storage and processing, is important for obtaining reliable and meaningful diagnostic information.