2 Tube Colors and Additives

Learn what common blood collection tube colors may indicate, how additives relate to specimen types and tests, and how to follow order-of-draw and handling requirements.

Interpreting tube colors

A tube’s color is a useful clue to its additive and likely specimen type, but it is not a universal guarantee of what the tube contains. Colors and additives can vary by manufacturer, facility, and test. Check the tube label and the laboratory’s current test instructions before collecting or processing a specimen.

Common tubes and their uses

Culture and coagulation tubes

Blood culture bottles or yellow (SPS): These use sterile bottles or sodium polyanethol sulfonate (SPS) and commonly produce in culture medium. They are used for blood cultures to detect bloodstream infection.
Light blue: These contain and produce citrated . Common coagulation tests include PT/INR and aPTT.

tubes

Red: Some glass tubes have no additive, while some plastic tubes contain a clot activator. They produce and are used for selected chemistry, serology, and immunohematology tests.
Gold or tiger-top (SST): These contain a clot activator and gel separator, produce , and are used for many chemistry and serology tests.
Orange (RST): These contain a rapid clot activator, commonly thrombin, and produce for selected tests needing rapid preparation.

Other anticoagulant and specialty tubes

Green: These contain heparin, commonly lithium or sodium heparin, and produce heparinized or sometimes . They are used for selected chemistry tests; exact use depends on the test.
Lavender or purple: These commonly contain K₂ or K₃ and produce or sometimes . Common uses include CBC and other hematology tests, as well as HbA1c in many laboratories.
Pink: These contain , often in a blood-bank-specific formulation, and produce for blood-bank testing such as type and screen.
Gray: These commonly contain sodium fluoride with potassium oxalate, or another glycolysis-inhibiting formulation. They produce or , depending on processing, for glucose and selected tests requiring glycolysis inhibition.
Yellow (ACD): These contain acid citrate dextrose (ACD) and produce for selected specialized tests, such as certain cellular or genetic studies.
Royal blue: These may be plain, , or heparin tubes and are often designed to minimize trace-element contamination. They may produce , , or for trace-element and metal testing; use the exact tube specified by the test.
Black: These commonly contain in a specialized tube and produce citrated for erythrocyte sedimentation rate (ESR), where specified.

is the liquid portion collected after blood clots. is the liquid portion of anticoagulated blood after cells are separated. is unseparated blood and is generally collected in an anticoagulant tube when required.

When collecting multiple tubes during one venipuncture, the usual sequence is:

Sterile blood cultures.
Light blue — citrate.
tubes — red, gold or tiger-top, or orange, as applicable.
Green — heparin.
Lavender or purple, or pink — .
Gray — glycolysis inhibitor.

Specialty tubes, including royal blue and yellow ACD tubes, must be placed according to their additive and the laboratory’s instructions. Follow the facility’s approved ; protocols can differ for specific collection systems and tests. The sequence helps reduce additive carryover. For example, contamination can interfere with results from another tube.

Collection and handling

The requested test determines the correct additive, specimen type, tube, volume, and processing conditions. Tubes are not interchangeable just because their colors look similar. Fill each tube to the required volume; this is especially important for light-blue citrate tubes because the blood-to-additive ratio is critical for reliable coagulation results. Underfilling can invalidate a specimen.

Mix additive tubes gently and promptly, inverting them the number of times specified by the manufacturer or laboratory. Do not shake, because vigorous mixing can damage blood cells. Tubes without anticoagulant generally need time for clotting before centrifugation.

Process and transport specimens as directed. Depending on the test, a specimen may need to be centrifuged, separated from cells, protected from light, kept at a particular temperature, or delivered within a specified time. Requirements are test-specific.

Label each tube at the patient’s side according to facility policy, and check that the label and requisition match. For special testing, use the specified collection container. For example, trace-element testing may require a particular metal-free tube; a generic royal-blue tube may not be acceptable.

Applying the tube guide

A CBC commonly uses a lavender-top whole-blood specimen. A PT/INR commonly uses a light-blue sodium-citrate specimen and requires the tube to be filled correctly. A glucose test may use a gray-top tube when that is what the laboratory specifies. In each case, confirm the exact test instructions rather than relying on color alone.