Tube Colors And What They Mean
In this section, we run through the various tube colors phlebotomists use to denote specific types of draws. The tube color refers to the color of the stopper used to cap the tube, not the color of the cylindrical tube material itself.
A gray stopper indicates a tube that contains any of the following chemicals:
- Potassium oxalate
- Sodium fluoride
- Na2 EDTA
Labs typically use gray lids for glycolic inhibition of draws. Gray tops are common when phlebotomists expect there to be a delay in glucose level test results.
Gray tubes are used to test blood levels for various compounds. These include:
- Blood alcohol levels
- Glucose levels
- Bicarbonate levels
- Lactate level
Medics may also use them for lipid panels (to determine a patient’s risk of heart disease), liver function tests, electrolyte analysis and monitoring of therapeutic drugs.
PhlebotomyU offers several courses. In our CPT I classes, students will receive hands on experience and practice this procedure in clinical and classroom settings. Contact PhlebotomyU today to learn which course is best for you.
Lavender/purple-topped tubes are for draws that require the use of ethylenediaminetetraacetic acid (EDTA) to bind calcium ions and block coagulation.
The tubes come pre-lined with various types of EDTA depending on the application. They keep white blood cells, platelets and other blood constituents stable (without coagulation) for up to 24 hours.
In many cases, there is no need to open purple tubes. Manufacturers design them for direct sampling.
Phlebotomists will select lavender/purple tubes for the following test:
- White blood cell count
- Red blood cell count
- Platelet count
- Eosinophil count
- Erythrocyte sedimentation rate
- Tests for sickle cells
- Hemoglobin levels
Green-topped phlebotomy tubes have either ammonium heparin, lithium heparin, or sodium herpin coatings on their inside surfaces. These anticoagulants activate anti-clotting agents in the blood, blocking coagulation cascades. They are suitable for either plasma or whole blood.
These tubes are usually used for:
- STAT chemistry
- Clinical chemistry
However, there are certain situations in which they should not be used. They are inappropriate for any blood banking procedures. Furthermore, ammonium heparin tubes should not be used for ammonia determinations, lithium heparin for lithium measurements and so on.
Red stoppers denote draws for serology and immunohematology. Plastic red-topped tubes typically have clot activators on their interior surfaces, while glass versions don’t.
To activate red-topped tubes, phlebotomists must invert them several times to mix the solution. Clotting usually occurs within around 30 minutes.
Red-topped tubes have multiple serology applications including:
- Strep testing
- Cold agglutinins
- C-reactive protein
- Rubella titer
Phlebotomists will also use red stoppers for immunotherapy applications to check for patient compatibility before a transfusion.
Light Blue Top
Light blue-topped tubes come with two main additives: CTAD (Citrate, theophylline, adenosine, dipyridamole) and sodium citrate at concentrations of 3.2 or 3.8 percent.
The calcium citrate is a powerful anticoagulant that binds to the calcium in the blood required for clotting. How much of the chemical the tubes contain is very much a function of the specifications of the manufacturer. Some are more liable to increase calcium citrate levels than others.
Light blue-topped tubes are used in a variety of tests. These include:
- Fibrin degradation products
- Thrombin time
- Prothrombin time
Phlebotomists use yellow-topped tubes for DNA studies – such as paternity tests – and HIV cultures. The solution typically consists of a combination of citric acid, dextrose and trisodium citrate.
Tan-colored tubes are used in tests for lead levels. The tubes are coated in K2 EDTA .
Sometimes, phlebotomists will use multiple different colors of vials for the same tests. Blue, purple and pink-topped tubes are sometimes interchangeable with yellow.
Pink, for instance, is commonly used for:
- HIV viral load tests
- Compatibility studies
- Blood type and screening
Royal Blue Top
Royal blue-capped tubes have no additives and are usually made of special glass or plastic that will not contaminate the specimen. Phlebotomists use royal blue tubes to test:
- Drug levels
- Concentration of trace elements in the bloo
Royal blue tubes are ideal for tests that do not require either coagulation or anticoagulation to generate reliable results.
Phlebotomists use pearl tubes for HHV-6, adenovirus and toxoplasma PCRs. Typically they contain a separating gel and EDTA. Pearl tubes typically draw 6 ml, with a minimum of 4 ml
Lastly, gold-topped tubes contain a separating (serum separator – SST) gel and clot-activation compounds. Phlebotomists use them for a broad array of tests, including hepatitis, HIV, serology and endocrinology testing. Vials usually have a capacity of 6 ml making them considerably larger than yellow vials, which have a maximum capacity of 2 ml.
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