Veterinary nurses are responsible for obtaining and submitting patient blood samples for diagnostic testing, and they must be familiar with laboratory test requirements to ensure that correct sample types and amounts are collected in appropriate tubes. Improper collection and tube selection can adversely affect test results, causing potential misdiagnosis and delaying patient treatment.
Blood collection tubes are distinguished by top colour, which identifies tube additives. Tube additives prevent or activate clotting and determine the final blood product submitted for testing.
Whole Blood
Whole blood consists of plasma, red and white blood cells, and platelets and is required for complete blood counts. Whole blood is collected in lavender and green top tubes.
Lavender Top Tubes
Lavender top tubes contain EDTA, an anticoagulant. Make sure the blood sample is mixed well with the EDTA to avoid sample clotting. Do not shake the tube, as this can damage cell structure. Use lavender top tubes to submit whole blood for tests that examine red and white blood cells and platelets.
Green Top Tubes
Green top tubes contain heparin, an anticoagulant that acts by inhibiting thrombin formation.
Serum
Serum samples are required for blood chemistry panels, serology, immunology, and most endocrinology tests. Serum is the fluid portion of the blood that has had fibrinogen removed during clotting. Blood for serum testing is collected in red or red/grey top tubes.
Red & Red/Grey Top Tubes
These are serum separator tubes and are commonly used for any test requiring serum.
Plastic red top and marble top tubes contain a gel to separate serum from the clot and a clot activator but no anticoagulants or preservatives.
Plasma
Plasma is required for blood chemistry, coagulation, platelet function, and some toxicology tests. Plasma is the liquid portion of the blood from which the red and white blood cells and platelets have been removed. Plasma consists primarily of water with dissolved proteins, hormones, lipids, enzymes, salts, carbohydrates, vitamins, and waste materials. Lavender, blue, and green top tubes are used to collect samples for plasma testing.
Green Top Tubes
Green top tubes contain heparin; once centrifuged, the supernatant is considered heparinized plasma. This tube should be used for blood chemistry analysis and toxicology testing for some metals and nitrates.
Light Blue Top Tubes
Light blue top tubes contain an anticoagulant called sodium citrate, which removes calcium from the blood to prevent clotting. Use light blue top tubes for testing prothrombin time, activated partial thromboplastin time, and fibrinogen.
Conclusion
Blood samples must be properly collected, handled, and labeled to ensure accurate diagnosis and treatment of veterinary patients. Veterinary nurses must be familiar with the sample requirements (including proper tube, sample amount, and sample type) of each diagnostic test ordered by the veterinarian.
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