Tube and additive lookup
Each blood collection tube carries an additive that determines both what it can test and where it falls in the order of draw. Sodium citrate and EDTA bind calcium to stop clotting, heparin inactivates thrombin, clot activators do the opposite and make the blood clot for serum testing, and sodium fluoride with potassium oxalate preserves glucose. The closure colour is a convention, not a standard, and varies by manufacturer.
The full venipuncture set, in the order they are drawn.
Pool for this variant: 6 items. A real draw is 6.
Colour conventions vary between manufacturers; confirm against your own laboratory. Inversion counts come from the tube manufacturer, not from CLSI or WHO.
How this works
Tubes are listed in the CLSI order of draw. Additive names, mode of action and the tests each serves come from the WHO phlebotomy guidelines, whose Table 2.3 sets them out; the sequence itself follows CLSI, because WHO's table is based on the 2003 NCCLS consensus and is superseded on that point. Closure colours are given as the common conventions, and WHO instructs verifying them against your own laboratory because they vary between manufacturers. Per-tube inversion counts are not listed: neither source publishes them, and NHA task 3N refers you to the tube manufacturer.
Worked examples
A gray top tube preserves glucose because sodium fluoride inhibits glycolysis, which is why a glucose drawn into the wrong tube reads low after sitting. A light blue citrate tube must be filled completely, because the test depends on the ratio of citrate to blood rather than on the absolute amount of either.
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Primary references
- WHO Guidelines on Drawing Blood: Best Practices in Phlebotomy — World Health Organization · government · retrieved 2026-09-22, verified 2026-09-22
- Order of Blood Draw Tubes and Additives — Clinical and Laboratory Standards Institute (CLSI) · primary · retrieved 2026-09-22, verified 2026-09-22
- NHA Certified Phlebotomy Technician (CPT) — Test Plan for the CPT Exam — National Healthcareer Association (NHA) · primary · retrieved 2026-09-22, verified 2026-09-22