How Phlebotomy Tubes Are Used to Prevent Blood Contamination
In the field of phlebotomy, a variety of tubes are used to draw blood specimen for certain testing procedures. While the number of colors seem overwhelming to ordinary folks, health care professionals are trained to perform blood collection and differentiate one test tube from another as required by the specimen to be drawn. They are also aided by the order of draw (http://www.ncbi.nlm.nih.gov/books/NBK138665/table/ch2.t3/?report=objectonly) as recommended by the Clinical and Laboratory Standards Institute (CLSI).
Vacutainer tubes, as they are collectively called, were developed by Joseph Kleiner in 1947 and are currently being produced by Becton, Dickinson and Company, a global provider of medical supplies to the healthcare and pharmaceutical industry.
Different phlebotomy tubes are identified by the color of the stopper or shield. Specific colors indicate a presence of certain additives. They are categorized as tubes for coagulant blood tests, anticoagulant blood tests and other types of tests.
Coagulant Blood Test
Tubes under this category are often used in patients with a bleeding disorder or are using a blood thinner medication. Tests are performed to check their ability to clot properly. Some of the tubes used have the following stopper/shield colors:
- Gold or red/gray tube, also known as a tiger tube that contains a clot activator. It is used to separate blood from the serum.
- Tubes with a red stopper are used to collect serum to test for routine donor screening or infectious disease. It contains a clot activator.
- Tubes with orange or gray/yellow tops are used to test serum that is needed right away. It contains a rapid clot activator known as thrombin.
Anticoagulant Blood Test
Performing an anticoagulant blood test requires a different type of tube, one that don’t contain a clot activator. Instead, it contains an additive that binds to calcium ions, inhibiting the proteins that lead to coagulation of blood specimens. Some of the tubes used are those with light blue, green, gray, dark blue and lavender or pink stoppers.
Other Types of Test
Other tests that are not classified as anticoagulant or coagulant use different tubes that contain specific additives or no additive at all. A tube with a red stopper does not contain additives and is used for testing for antibodies and drugs. There are also tubes with light yellow, tan and white stoppers.
Phlebotomy Tubes Explained
Yellow Top Tube
Yellow top tube contains sodium polyanethol sulfonate and is used for blood culture specimens or acid-citrate-dextrose (ACD solution A or ACD Solution B). The same tubes are used for HLA phenotyping and for conducting parental tests.
Blood culture tubes and vials also come in stoppers other than yellow. Vials with blue, purple and pink top contain enriched soybean-casin broth with CO2. Aside from bacterial, they are used in fungal blood cultures.
Light Blue Top Tube
Tubes with light blue stoppers/shields contain two additives: sodium citrate (3.2% or 3.8%) and CTAD (Citrate, theophylline, adenosine, dipyridamole). As an anticoagulant, citrate binds the calcium in blood that is needed for clotting. Since the additive still results in a whole blood sample — plasma and red blood cells, the coagulation tubes also contain buffered tri-sodium citrate solution. The amount of citrate concentration depends on a laboratory’s policies.
Some of the tests performed using the light blue top tube include routine coagulation with Prothrombin Time (PT), Partial Thromboplastin Time (PTT), Thrombin Time (TT), Fibrinogen, Fibrin degradation products (FDP) and D-dimer.
Red Top Tube
Tubes with red-colored stoppers are used for serology and immunohematology. Glass tubes don’t contain additives, but those made of plastic have clot activators. Plastic tubes need to be inverted to mix the blood with the coagulant. It usually takes 30 minutes for clotting to occur. Serology is done to check infectious mononucleosis, rheumatoid arthritis, syphilis, rubella titer, strep testing, pregnancy test, cold agglutinins, haptoglobin and C-reactive protein.
In immunohematology, a patient’s blood is tested for compatibility, where the components are prepared for transfusion. Some of the requested components include packed red blood cells, platelets, cryoprecipitate and fresh frozen plasma.
Green Top Tube
Phlebotomy tubes with green top contain sodium herapin, lithium herapin and ammonium herapin, all of which are coated in the inside of the tube. The herapin anticoagulant activates antithrombins that block the coagulation cascade and produce a plasma sample or whole blood. The same tubes are used for clinical chemistry and STAT chemistry tests.
There are instances, however, where herapin-filled plasma tubes should not be used.
- TDM measurements
- Lithium heparin for lithium determinations
- Sodium heparin for sodium determinations
- Ammonium heparin for ammonia determinations
- Any type of heparin for blood banking procedures
Tubes with a green stopper with a yellow ring on top are called a Plasma Separator Tube (PST). They contain a gel that separates plasma from the cells when centrifuged, and are used for a wide range of testing. Serum separator tubes make an acceptable substitute for PST.
Purple or Lavender Top
Tubes with purple or lavender-colored stoppers contain EDTA (ethylenediaminetetraacetic acid) additive that binds calcium ions, effectively blocking coagulation cascade. Clinical laboratories use these to test for whole blood. It can come with either EDTA K2 or EDTA K3 (http://www.ncbi.nlm.nih.gov/pubmed/1794231) additive that coats the interior of the tube. The former is used to test whole blood in molecular diagnostics. EDTA tubes are used in direct sampling analyzers without the need to open them. For up to 24 hours, erythrocytes, white blood cells and platelets remain stable in blood anticoagulated with EDTA, but blood smears must be prepared 3 hours after specimen is collected.
Routine hematology tests that use EDTA tubes include hemoglobin, hematocrit, white blood cell, red blood cell, and platelet count, reticulocyte count, eosinophil count, body fluid counts, sickle cell test, and erythrocyte sedimentation rate.
Gray Top Tube
Gray-colored stoppers indicate that the tubes can contain potassium oxalate and sodium fluoride, sodium fluoride, and sodium fluoride/Na2 EDTA. These are often used for laboratory procedures where glycolytic inhibition of specimen is needed. Although red top tube can be used for a similar procedure, gray top tubes are preferred when there is a delay in having the glucose level tested. For adequate mixing of blood and additive, the tube must be inverted 4 to 5 times after specimen is collected.
Generally, phlebotomy tubes with gray stoppers are used to test glucose levels, lactate, bicarbonate and blood alcohol levels. In clinical chemistry, however, it is used for a wide range of specialized and routine procedures. These include tests for the following:
- Lipid panels
- Hepatic function tests
- Markers of cardiac damage
- Protein electrophoresis
- Evaluation of endocrine and metabolic disorders
- Therapeutic drug monitoring and toxicology
Aside from these, there are blood collection tubes with slight variations in color. Tubes with pink stoppers, for example, are used in blood banks for different procedures, such as cross-matching, screening of anti-bodies or blood typing. Those with royal blue stoppers are mainly used for toxicology, nutritional studies and analysis of trace metals as they are metal-free. Serum separator tubes also have red stoppers but with a yellow ring on top. It contains a gel that effectively separates the cells from the serum when run through centrifugation.
How these phlebotomy tubes are used follow the order of draw.
- Blood culture
- Coagulation tubes
- Non-additive tubes
- Additive tubes
The order may seem simple, but not when the color-coded tubes come into play. Nonetheless, phlebotomy technicians are trained to use each one and collect blood specimen with utmost care.