Sample Collection and Handling for Chemistry Testing

Importance of correct sample collection techniques for accurate laboratory results:
Effective sample collection techniques are crucial for ensuring the integrity and reliability of laboratory results. Any deviation from established protocols can lead to erroneous test outcomes, impacting diagnosis, treatment decisions, and patient care. Understanding the nuances of sample collection, including timing, technique, and equipment, is essential for laboratory professionals and healthcare providers.

CHEMISTRY TESTING

Types of blood samples useful in tests:

  • Whole blood: Utilized for a variety of diagnostic tests, including complete blood counts (CBC) and blood culture tests, which require both cellular components and plasma. Whole blood is collected in specific tubes to preserve cellular integrity.

  • Plasma: This component is derived from whole blood through centrifugation. It consists of water, electrolytes, proteins, hormones, and waste products. Plasma is used in testing for electrolytic balance, liver function tests, and certain hormonal assays.

  • Serum: Similar to plasma but devoid of clotting factors, serum is obtained by allowing blood to clot and then centrifuging. It is commonly used in biochemical tests for metabolic panels, liver function tests, and serological assays to detect antibodies.

ANTICOAGULANTS

Common anticoagulants used in blood sample preparation:

  • Heparin: A naturally occurring anticoagulant that prevents blood clotting; suitable for plasma samples, especially in tests involving electrolytes and metabolic panels.

  • EDTA (Ethylenediaminetetraacetic acid): A potent anticoagulant that preserves blood cell morphology, making it essential for hematology tests such as CBC.

  • Oxalates: Used in specific tests where calcium binding is needed; they prevent clotting by precipitating calcium.

  • Sodium fluoride: Primarily used to inhibit glycolysis, it helps maintain glucose levels in samples for diabetes-related tests.

  • Sodium citrate: Commonly used for coagulation studies; it requires specific blood-to-additive volume ratios to be effective in preventing coagulation.

VOLUME OF SAMPLE

Factors influencing the volume of sample collected:

  • Hydration of patient: Proper hydration can influence blood volume, which in turn affects laboratory test results. Dehydrated patients may exhibit higher concentrations of certain analytes.

  • Amount required for tests: Different laboratory tests demand varying volumes of blood; therefore, it is crucial to consult specific laboratory protocols to ensure adequate sample size.

  • Fasting: For biochemical tests, fasting is essential as it can significantly influence the concentration of certain markers, such as glucose and lipids, thereby affecting interpretation.

COMMON LABORATORY ERRORS

  • Hemolysis: The breakdown of red blood cells, which can lead to interference in serum tests by causing abnormalities, particularly in potassium, lactate dehydrogenase (LDH), and other pivotal tests.

  • Lipemia: The presence of excess lipids in the serum can falsely elevate certain measurements, such as triglycerides and cholesterol, impacting the clinical interpretation of lipid profiles.

Effects of Temperature on Blood Samples:

  • Blood samples stored at inappropriate temperatures may not clot properly; refrigerated samples may yield erroneous results for serum tests.

  • Fibrin clots can occur if blood samples are centrifuged too quickly or too slowly, compromising sample integrity.

  • Samples, particularly serum, frozen at suboptimal conditions may remain stable for about 6 weeks for most constituents but should be stored correctly to ensure reliability.

  • Glucose levels in blood samples can deteriorate rapidly, decreasing approximately 7% per hour at room temperature; hence, timely processing is crucial.

  • It is imperative that samples are separated within 30 minutes of collection to preserve accuracy in test results.

ORDER TO DRAW AND FILL TUBES

The order of draw can differ based on updates in protocols and compliance; referencing specific guidelines from textbooks is recommended (e.g., Pg 40).
It is advised to invert blood collection tubes 8 times after collection to facilitate proper mixing of additives, which is critical for test validity.

PLASMA COLOR AND CLARITY

Observations required upon analysis:

  • Normal: Should present as clear and pale yellow; indicates proper collection and processing.

  • Lipemic: Indicates a cloudy appearance due to high fat levels, which may interfere with certain tests.

  • Hemolyzed: Appears pink/red due to hemolysis; it can significantly affect test results and interpretation, leading to false abnormalities.

  • Icteric: Presents a yellow hue caused by elevated bilirubin levels, often indicating liver dysfunction or certain hemolytic conditions.

  • The Visual Hemolysis Grading Chart is essential in noting transparency, with grades ranging from 1+ to 4+ depending on the severity of hemolysis, directly impacting result interpretations.

QUESTIONS?

Encourage patients to ask questions regarding preparation or procedures to ensure clarity and compliance, fostering a better understanding of their testing processes and addressing any concerns they may have regarding their health and the implications of testing outcomes.