1 Blood Collection Tubes and Specimen Basics

Why tube choice matters

A blood collection tube is designed to produce a particular specimen—serum, plasma, or whole blood—and preserve it for specific tests. Its additive may prevent clotting, help blood clot, separate cells from liquid, or protect an analyte from change.

Choosing the wrong tube, filling it incorrectly, or mixing it improperly can alter results or make a specimen unsuitable. Use the test’s required additive and specimen type as the basis for selection, rather than relying on cap color alone. Colors and additives can vary by manufacturer and laboratory, so check the laboratory’s test directory or collection guide whenever requirements are uncertain.

Common tubes and their uses

These are common examples, not a substitute for a test-specific collection requirement. A color alone does not identify every tube’s contents or suitability.

• Blood culture bottles or designated culture tubes: Contain culture medium; some culture tubes contain SPS. Use them for blood cultures and collect using the required sterile technique.

• Light blue: Contains sodium citrate and yields citrated plasma for coagulation tests such as PT/INR, aPTT, and D-dimer. Fill to the indicated volume so the blood-to-additive ratio is correct.

• Red: May contain no additive or a clot activator, depending on the tube. Used to obtain serum for many chemistry, serology, and reference tests; check the tube type and laboratory instructions.

• Gold or tiger-top (SST): Contains a clot activator and separator gel. Used for serum in many chemistry and immunology tests. Allow clotting as directed before centrifugation.

• Green: Commonly contains lithium or sodium heparin. Used for plasma or whole blood in selected chemistry tests. The heparin salt matters for some tests; for example, a lithium-containing tube is generally unsuitable for measuring lithium.

• Light green (PST): Contains lithium heparin and separator gel and is used for heparinized plasma in selected chemistry tests.

• Lavender or purple: Commonly contains K₂EDTA or K₃EDTA. Used for whole blood in hematology tests such as a CBC; some tests use EDTA plasma.

• Pink: Commonly contains K₂EDTA and is often used for blood-bank testing, such as blood type and antibody screen. Follow the blood bank’s identification and collection rules.

• Gray: Commonly contains sodium fluoride with potassium oxalate, although formulations vary. Used for selected glucose testing and other tests specified by the laboratory. Its additives help inhibit glycolysis and/or prevent clotting.

• Yellow: May contain ACD or SPS, depending on the tube and its use. ACD tubes are used for selected genetics or special studies; SPS tubes may be used for blood cultures. Confirm the additive, not just the color.

• Royal blue: May be additive-free or contain EDTA or another additive. Used for trace-element or other specialized testing; select the version specified by the laboratory.

Order of draw

When collecting multiple tubes during one venipuncture, use the laboratory’s approved Order of draw. A commonly used sequence is:

1. Blood cultures.

2. Light blue—citrate.

3. Serum tubes—red, then gold or tiger-top as applicable.

4. Green or light green—heparin.

5. Lavender or purple, or pink—EDTA.

6. Gray—fluoride/oxalate or the laboratory’s specified gray-tube additive.

7. Yellow ACD and other special tubes, in the order specified by the laboratory.

This sequence helps reduce additive carryover from one tube into the next. Carryover can interfere with testing; for example, EDTA contamination can affect calcium or potassium measurements. Special tubes, including royal-blue tubes and some yellow tubes, may need to be placed according to their specific additive. Local procedures may differ, so follow the current facility guide.

If a winged collection set is used and a light-blue citrate tube is the first specimen, the tubing may need to be primed with a discard tube so air in the tubing does not cause the citrate tube to be underfilled. Follow local instructions; a discard tube is not automatically required for every collection method.

How additives affect specimens

Anticoagulants prevent clotting, but they work differently and are not interchangeable. Citrate binds calcium reversibly and is used for coagulation testing; EDTA binds calcium strongly and is commonly used for blood-cell analysis; heparin prevents clot formation through its effects on clotting factors.

Clot activators help blood clot so serum can be obtained. When present, separator gel forms a barrier between cells and serum or plasma after centrifugation. Fluoride-containing additives slow glycolysis, helping preserve glucose in some collection conditions; the required tube and processing time depend on the test and laboratory procedure. ACD preserves blood cells for selected specialized studies, and its use is test-specific.

For tubes with additives, gently invert each tube the number of times stated by the manufacturer or laboratory. Do not shake: vigorous mixing can damage blood cells and contribute to hemolysis. Do not pour blood from one tube into another, because this changes the additive-to-blood ratio and can contaminate the specimen.

Serum, plasma, and whole blood

• Serum: The liquid remaining after blood clots and the clot is removed. It is commonly collected in red or serum-separator tubes.

• Plasma: The liquid portion of anticoagulated blood, separated from blood cells. The anticoagulant used depends on the test.

• Whole blood: Blood cells and liquid together. It is commonly used for a CBC in an EDTA tube.

Collection, labeling, and handling

Before collection, verify the requested tests and any preparation or special-handling instructions. Identify the patient using the required identifiers, match the request to the patient, and choose the specified tube and volume. Use the approved collection procedure and infection-control precautions.

After collection, mix additive tubes gently as directed. Label each tube with the required patient identifiers and collection information before leaving the patient. Transport and process specimens as required; some tests need special timing, temperature, light protection, or other handling. Follow the laboratory’s test directory for these details.

Common specimen-quality problems

Common problems can compromise specimen quality or test results:

• Wrong tube or additive: May interfere with the test or make the specimen unacceptable.

• Underfilled tube: Can produce an incorrect blood-to-additive ratio, especially in citrate tubes.

• Clotted anticoagulated specimen: May result if the tube is not mixed promptly and gently as instructed.

• Hemolysis: Damaged red cells can release their contents and affect some test results; avoid vigorous shaking and rough handling.

• Mislabeling or delayed or inappropriate handling: Can compromise patient identification or alter the analyte being measured.

Correct tube selection, filling, gentle mixing, accurate labeling, and prompt test-appropriate handling help preserve specimen quality and support reliable results.