Parameters:
(1) draw volume observed as percent of reported
(2) stopper features of a filled tube (looseness, leakage)
(3) breakage of a tube during centrifugation
(4) amount and type of additive
Testing the draw volume:
(1) A biuret with a stopcock at the bottom is connected by plastic tubing to a needle port for entry into an evacuated specimen tube.
(2) Deionized water is used to fill the tube and biuret, with removal of all air from the tubing. The stopcock is closed and the volume of the biuret is recorded.
(3) The needle is placed into an inverted vacutainer, the stopcock is opened and the tube is then allowed to fill.
(4) The meniscus in the filled (and still inverted) tube is placed at the same height as the meniscus in the biuret. The stopcock is closed and the final volume in the biuret is recorded.
fill volume of tube observed in mL =
= (original volume in mL) - (final volume in mL)
percent of predicted fill volume =
= (fill volume observed) / (fill volume claimed) * 100%.
Ideally the evacuated tube should have a fill volume +/- 10% of that claimed.
