What Tube for a PT/INR (prothrombin time)?
Light blue-top tube with 3.2% sodium citrate, filled to the line.
- Additive
- 3.2% sodium citrate
- Inversions
- 3–4 times
- Order of draw
- #2 of 6
Collection and handling
- The tube must keep a 9:1 blood-to-anticoagulant ratio, so fill it to the etched line; underfilled tubes are rejected.
- Underfilling leaves too much citrate and gives falsely long clotting times.
- Invert 3–4 times. Keep at room temperature (ARUP: do not refrigerate). Hemolyzed or clotted samples are rejected.
Exam tip
With a butterfly set, if the light blue tube is the first tube, draw a discard tube first so tubing air does not underfill it.
Where it falls in the order of draw
- 1. Blood culture bottles (aerobic + anaerobic) (Culture media)
- 2. Light blue (3.2% sodium citrate)
- 3. Gold / red-gray (SST) or red (Clot activator (SST also has gel))
- 4. Green / light green (PST) (Lithium heparin (PST also has gel))
- 5. Lavender (or pink) (K2EDTA)
- 6. Gray (Sodium fluoride / potassium oxalate)
Full explanation in the order of draw guide.
Tube requirements differ between labs and assays. Always follow your own laboratory's collection manual.
Drill tubes and order of draw until they stick
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