Introduction: Lithium concentrations analyzed from blood collected in inappropriate tubes may lead to misdiagnosis and lead to unnecessary hospitalization and intervention. We sought to assess the magnitude of falsely elevated lithium levels in green top lithium heparin-containing blood tubes.
Methods: Serum lithium concentrations from two types of commonly used standard green top tubes were evaluated against a control tube. Blood samples obtained from 5 healthy volunteers who have never ingested pharmaceuticals containing lithium were aliquoted into a control serum separator tube (SST), a light green heparin-containing tube, and a dark green heparin tube at the following volumes: full draw, 2cc, and 1cc. Serum lithium levels in lithium heparin blood tubes were compared to standard blood tubes.
Results: All levels are reported as mmol/L. Mean serum lithium level for the control was 0.16 [range: 0.1-0.2]. Levels for the light-green tubes at full-draw, 2cc, and 1cc were 1.05 [1.0-1.1], 1.99 [1.68-2.3], and 3.31 [2.8-4.2] respectively. Levels for the darkgreen tubes at full-draw, 2cc, and 1cc were 1.07 [1.0-1.14], 2.35 [2.1-2.55], and 4.04 [3.8-4.4] respectively.
Conclusions: Falsely elevated lithium levels may occur when using green-top lithium containing blood tubes and may contribute as much as 4 mmol/L to the level in tubes not completely filled.