Phlebotomy tube colors and additives
What each blood collection tube color means: the additive, the tests it is used for, and where it falls in the order of draw. A study reference for the NHA CPT exam.
Each stopper color tells you what is inside the tube, which tests it is for and where it fits in the order of draw. Colors vary a little by manufacturer, so the additive is the fact to learn. The table below covers the tubes the NHA CPT exam expects you to know; the tube color guide lets you search it by test.
| Tube | Additive | Typical use | Order of draw |
|---|---|---|---|
| Blood culture bottle (yellow SPS) | Broth mixture that keeps organisms alive | Blood cultures | 1 |
| Light blue | 3.2% sodium citrate (binds calcium) | Coagulation tests such as PT/INR and aPTT | 2 |
| Red | No additive in glass; usually a clot activator in plastic | Serum tests | 3 |
| Gold or red-speckled (SST) | Clot activator plus separator gel | Serum chemistry, serology | 3 |
| Green | Heparin, with or without gel | Plasma chemistry, stat chemistry | 4 |
| Lavender | K2 EDTA (binds calcium) | Hematology such as a CBC | 5 |
| Gray | Sodium fluoride plus potassium oxalate | Glucose, lactate, blood alcohol | 6 |
| Pink | EDTA | Blood bank: type and screen, crossmatch | Follow your lab's chart |
| Yellow (ACD) | ACD solution A or B | Genetic and HLA testing | Follow your lab's chart |
| Royal blue | Certified for trace-metal testing | Trace metals | Follow your lab's chart |
| Tan | K2 EDTA | Lead testing | Follow your lab's chart |
| Black | 3.8% sodium citrate | Westergren ESR only | Follow your lab's chart |
The four additive ideas
Most of the table collapses into four kinds of additive:
- Anticoagulants that bind calcium: EDTA (lavender, pink, tan) and citrate (light blue, black). Without calcium, blood cannot clot.
- Heparin (green): blocks thrombin, so the blood stays liquid and gives plasma.
- Clot activators and gels (red, gold, orange): speed clotting so you get serum, and the gel separates the serum from the cells.
- Antiglycolytic agent (gray): fluoride stops the cells from consuming glucose after the draw, which is why glucose and lactate go here.
Common exam traps
- A light blue tube has a strict blood-to-additive ratio of 9 to 1, so a short draw ruins the result. Gray tubes also need a full draw.
- A lavender tube that is not mixed can clot or show platelet clumping, so invert it 8 to 10 times gently.
- Yellow can mean two different things: the SPS in a culture bottle, or ACD solution for genetic testing.
- Lavender EDTA carried into a serum or heparin tube can raise potassium and lower calcium, which is why the order of draw exists. See the order of draw, explained.
Learn it for the exam
Tube colors are pure recall, so they suit spaced repetition. Unit 6 of the NHA CPT phlebotomy course covers tubes, additives and the order of draw, and the order of draw quiz tests the sequence. For the whole exam, read what is on the NHA CPT exam and how to study for the NHA CPT exam.
Blood Draw Tube Color Guide
Look up a collection tube by color, additive or test, with its order-of-draw step.
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