Routine Blood Collections: practice questions

Correct: A. CLSI places the coagulation tube second, straight after blood cultures. The sequence runs cultures, citrate, serum with clot activator and gel, heparin, EDTA, then fluoride-oxalate last.

• B — EDTA sits fifth. Drawing it early risks carrying potassium and EDTA into later tubes.
• C — Serum tubes with clot activator sit third, after the citrate tube, not before it.
• D — The glycolytic inhibitor tube is drawn last in the sequence, not second.

Correct: B. This is the exception CLSI spells out explicitly, and it is exactly what a colour-list recitation misses. A clot activator is the disqualifier: a plastic serum tube may precede the coagulation tube only if it has none.

• C — A clot activator is precisely what disqualifies a serum tube from preceding the coagulation tube.
• D — EDTA binds calcium and would corrupt a coagulation result; it never precedes the citrate tube.
• A — Full filling matters for the citrate ratio but does not override the carryover rule.

Correct: C. The sequence prevents cross-contamination of additives between tubes. It runs from the tube most vulnerable to contamination toward the additives most likely to interfere.

• D — Vacuum in an evacuated tube is set at manufacture and does not depend on draw order.
• A — Instruments analyse what they are given; they cannot detect the order of collection.
• B — Sequence does not change the volume required for each individual test.

Correct: D. Both EDTA and citrate work by removing calcium, so EDTA carried into a citrate tube adds an uncontrolled anticoagulant to a test that depends on a precise citrate-to-blood ratio.

• A — The contamination travels forward from the tube drawn first, so it is EDTA reaching citrate.
• B — EDTA is an anticoagulant; it prevents clotting rather than activating it.
• C — Inversion mixes the additive already present; it cannot remove contamination from another tube.

Correct: A. Prolonged tourniquet application causes haemoconcentration and alters results. WHO adds that some guidance releases it as soon as blood flow is established, and never beyond two minutes.

• B — Releasing after withdrawal risks a haematoma, because the vein is still under pressure.
• C — Ten minutes is far beyond the point at which haemoconcentration affects the specimen.
• D — Leaving it in place without a limit is what the two-minute guidance exists to prevent.

Correct: B. Anchoring below the site stabilises the vein without the phlebotomist's hand lying in the needle's path. WHO describes holding the arm and placing a thumb below the site.

• C — Anchoring above places the hand in the path of the needle and does not stabilise the vein.
• D — Pressing over the site collapses the vein and contaminates a prepared insertion point.
• A — The two-handed technique puts a finger in the needle path and risks a needlestick.