When a blood sample is collected, different colored tubes are used. Each color signifies the presence or absence of specific additives within the tube. These additives are crucial for preparing the blood sample for various laboratory tests, ensuring it remains in the proper state for accurate analysis.
The Purpose of Different Tube Colors
Different colored blood collection tubes are used because specific laboratory tests require blood samples in various forms. The primary reason for this color coding lies in the additives contained within each tube. These additives either prevent clotting, promote clotting, or separate blood components.
Anticoagulants stop blood from clotting, keeping the sample liquid for tests requiring whole blood or plasma. Some tubes contain clot activators, which encourage rapid clotting to yield a serum sample. Other tubes include a gel separator, creating a barrier between blood cells and the liquid portion (serum or plasma) after processing. The chosen tube color directly influences the sample type and its suitability for diagnostic assays.
Common Blood Collection Tube Colors and Their Applications
The color of a blood collection tube cap indicates its contents and intended use. This guides healthcare professionals in selecting the correct tube for each test.
Red Top Tube
Some red top tubes contain a clot activator, while others have no additives. Blood collected in these tubes clots naturally, and after centrifugation, serum is obtained. This serum is commonly used for various biochemical tests, such as liver function panels, lipid profiles, and hormone assays.
Lavender/Purple Top Tube
Lavender or purple top tubes contain Ethylenediaminetetraacetic acid (EDTA) as an anticoagulant. EDTA prevents blood clotting by binding to calcium ions. These tubes are primarily used for hematology tests requiring whole blood or plasma samples, such as complete blood counts (CBC), blood cell morphology examinations, and blood typing. EDTA also helps preserve blood cell integrity, preventing clumping or breakage.
Light Blue Top Tube
Light blue top tubes contain sodium citrate as an anticoagulant. Sodium citrate prevents blood clotting by binding to calcium ions. These tubes are used for coagulation studies, such as prothrombin time (PT) and activated partial thromboplastin time (aPTT), which assess the blood’s clotting ability. Maintaining the correct blood-to-anticoagulant ratio is important for accurate results.
Green Top Tube
Green top tubes contain heparin as an anticoagulant. Heparin prevents blood clotting by inhibiting thrombin formation. These tubes are used for plasma determinations in chemistry, including electrolyte tests and certain enzymatic assays. They are also used for immediate blood chemistry results in emergency situations.
Gray Top Tube
Gray top tubes often contain sodium fluoride and potassium oxalate. Sodium fluoride acts as an antiglycolytic agent, preserving glucose levels by inhibiting its breakdown. Potassium oxalate functions as an anticoagulant by binding to calcium ions. These tubes are primarily used for glucose testing, such as fasting blood sugar and glucose tolerance tests, and also for lactate and blood alcohol level measurements.
Gold/Tiger Top Tube (Serum Separator Tube – SST)
Gold or “tiger top” tubes, also known as Serum Separator Tubes (SST), contain a clot activator and a gel separator. The clot activator promotes rapid blood clotting. The gel forms a barrier between the serum and blood cells after centrifugation, allowing for easy serum separation. Serum from these tubes is used for a wide range of chemistry, serology, and immunology tests, including basic metabolic panels, comprehensive metabolic panels, and lipid profiles.
Yellow Top Tube
Yellow top tubes often contain acid-citrate-dextrose (ACD) as an anticoagulant. ACD prevents clotting by chelating calcium ions and helps preserve red blood cell integrity. These tubes are primarily used for specialized tests such as blood bank studies, including blood typing and crossmatching, as well as Human Leukocyte Antigen (HLA) typing and DNA analysis.
Ensuring Reliable Test Outcomes
Using the correct blood collection tube color for each test is important for reliable results. If the wrong tube is used, additives can interfere with the analytical process, leading to inaccurate outcomes. This can result in sample rejection, requiring a re-draw and delaying diagnosis.
Healthcare professionals follow a specific “order of draw” when collecting multiple blood samples. This sequence ensures additives from one tube do not cross-contaminate subsequent tubes, maintaining specimen integrity. This protocol minimizes contamination risk and helps maintain sample quality.
The Journey of Your Blood Sample
After blood is drawn and collected, tubes are labeled with patient information for accurate tracking. Samples are then transported to the laboratory, often by courier or automated systems, under specific conditions to maintain integrity.
Upon arrival, samples are logged and prepared for testing. Many tests require the blood to be spun in a centrifuge, separating it into components like plasma, serum, and blood cells, depending on the tube additive. These separated components are then analyzed by specialized machines or manual methods, providing data for diagnosis.