An Update on Underfilled Tubes

Objective: Underfilled blood tubes (short draws) are often collected from children or those with poor venous access. In a pilot study, we investigated which tests among a large acute care panel could be reported on short draws.

Methods: Blood was drawn in BD vacutainers (short draw: 1 mL [33%-56% fill volume] vs complete draw: 1.8-3 mL [100% fill volume]) from 12 volunteers for 3 coagulation tests, 36 chemistry tests, and the complete blood count (CBC) with differential. Tests that were strong candidates for reporting did not have statistically significant biases between short and complete draws, whereas potential candidates had statistically significant biases that were small (<25% of total allowable error and less than desirable bias from biological variation). Biases that increased or decreased across concentration ranges invalidated reporting candidacy.

Results: Two coagulation tests, 14 chemistry tests, and 15 CBC components were strong candidates for reporting. There were 9 chemistry tests and 2 CBC components that were potential candidates for reporting.

Conclusions: Underfilled blood tubes, or short draws, may be valid collections for several coagulation, chemistry, and hematology tests-which may prevent additional unnecessary phlebotomy. Laboratories should perform their own studies to determine if short draws are acceptable for limited testing using their tube and instrument types.