Routine Blood Collections

Why it matters on this exam

Twenty-eight items, and the domain where task statements and knowledge statements interlock most tightly. The test plan lists eighteen tasks (3A to 3R) and twenty-one knowledge statements (k54 to k74) for this domain alone.

Key concepts

• The order of draw, from CLSI's published statement of GP41:

1. Blood culture tube or bottle
2. Sodium citrate tube (blue closure)
3. Serum tubes with clot activator and gels (red, red-speckled, gold closures)
4. Heparin tube with or without gel (dark green, light green, speckled green closures)
5. EDTA tube with or without gel separator (lavender, pearl, pink closures)
6. Sodium fluoride / potassium oxalate glycolytic inhibitor (gray closure)

CLSI's exception is worth memorising in its own right: only blood culture tubes, glass nonadditive serum tubes, or plastic serum tubes without a clot activator may be collected before the coagulation tube.

• Why the order exists. Carryover of additive between tubes changes results. Drawing EDTA before a chemistry tube contaminates it with potassium and EDTA, which is why the order runs from no additive to most interfering.
• The tourniquet. Standard application and removal procedures are task 3E. WHO's guidance is to release the tourniquet before withdrawing the needle, and always before it has been in place for two minutes or more.
• Insertion. Anchor the vein by holding the arm with a thumb below the site — never above, never across. WHO describes entering the vein at 30 degrees or less.
• Complications (k68, k69): syncope, diaphoresis, nausea, seizures, hematoma, petechiae, nerve pain. Task 3L requires recognising them and responding; task 3K requires discontinuing the draw when patient signs warrant it.
• Inversions. Task 3N requires mixing additives by inversion according to manufacturer guidelines, and that is the authority — see below.
• Capillary collection is a different order (3P, k72), and blood cultures are a third (k78).

Common mistakes

• Reciting a tube colour list without the exception. The coagulation tube position is the one CLSI carves out explicitly, and that is precisely what makes it examinable.
• Treating colour as the identifier. Colour coding varies between manufacturers; the additive is what determines position. WHO says directly: verify colour codes with your local laboratory.

The numbers we do not publish

Inversion counts per tube. Knowledge statement k59 includes "number of tube inversions", but neither CLSI's published article nor WHO's guidelines state a count per tube, and CLSI GP41 itself is not free to read. WHO's instruction is to invert additive tubes "for the required number of times (as specified by the local laboratory)", and NHA's own task 3N points at manufacturer guidelines.

So the answer the exam wants is the principle — invert, do not shake, follow the manufacturer — and the counts come off the tube manufacturer's insert in your own workplace. Prep sites that publish a fixed table are quoting one manufacturer without saying so.

Worked example

A requisition asks for a coagulation panel, a CBC and a glucose. Working down the CLSI order: the light blue citrate tube comes before the lavender EDTA tube, and the gray fluoride-oxalate tube comes last. Draw the EDTA first and citrate carryover is not the problem — EDTA carryover into the citrate tube is, because EDTA binds calcium and would corrupt the coagulation result. The sequence exists to protect the tube that is most sensitive to what came before it.