Effect of microcollection tube fill volume on common acute care tests

Microcollection tubes are frequently used in pediatric phlebotomy. We performed a pilot study to determine what clinical biochemistry and hematology tests can be reported on different microcollection tube fill volumes.

Blood was collected from 11 volunteers into Becton Dickinson (BD) Vacutainers® and microcollection tubes (BD Microtainers® and the Sarstedt Microvette® 300 FH) at different fill volumes (Filled: top line; Intermediate: second line; Short: third line. If there was no second or third line, 200 µL was used for short fills) for 36 clinical biochemistry tests and the complete blood count (CBC) with differential (23 components). At each fill volume, tests were strong candidates to report if they did not have statistically significant biases compared to results in Vacutainers®. Potential candidates had statistically significant biases that were small (median absolute bias < 25 % of total allowable error and less than desirable bias from biological variation). Tests were not candidates if biases were significant and large (median absolute bias ≥ 25 % of TEa or ≥ desirable bias). Biases that increased or decreased across concentration ranges invalidated reporting candidacy.

Twenty four clinical biochemistry tests were strong or potential candidates to report on all fill volumes, 7 were strong or potential candidates to report on some fill volumes and 5 were not candidates to report on any fill volumes. Seventeen CBC components were strong or potential candidates to report on all fill volumes, 2 were strong or potential candidates to report on some fill volumes and 4 were not candidates to report on any fill volumes.

While most tests were valid to report on different fill volumes, some were not. We encourage laboratories to perform their own studies on fill volumes.