Objective: Blood collection tubes with a clot activator are widely used in clinical laboratories. Unexpectedly high results in folate assays obtained on Siemens Advia Centaur XP analyzer triggered a need for an investigation of the effects of blood collection tubes on folate measurements.

Material and Methods: We investigated the potential assay interference of three types of plastic tubes with a clot activator; Vacutest REF11030 (Group A); Becton Dickinson (BD) Vacutainer CAT REF367896 (Group B);and BD Vacutainer SSTTM II Advance REF367953 (with gel) (Group C) tubes. Blood samples from apparently healthy 13 volunteers were drawn into these different tube types and serum folate concentrations were analyzed by Siemens Advia Centaur XP, Roche E-170, and Beckmann UniCel DxI800 immunoassay analyzers. The results were compared and p values <0.05 were considered as statistically significant.

Results: Folate values measured one Siemens Advia Centaur XP, were significantly higher in Group A (13.44 ± 4.56 ng/mL) than Group B (8.82 ± 3.33 ng/mL) or Group C (8.58 ± 2.83 ng/mL) tubes (p<0.001). No difference was found between the tube groups regarding Roche E-170 and Beckmann UniCel DXI800 analyzers (p>0.05). When serum folate levels drawn into Grup A tubes were compared with different analyzers, results obtained from Siemens Advia Centaur XP (13.44 ± 4.56 ng/mL) were higher than results obtained from Roche E-170 (9.15 ± 2.25 ng/mL) or Beckmann Unicell DXI800 (8.70 ± 3.00 ng/mL) analyzers (p<0.001).

Conclusion: Siemens folate reagent was significantly influenced by the contents of the Vacutest tube with a clot activator resulting in high results. Assay interferences born from blood collection tubes represent challenges to clinical laboratories because they are not detected by the usual quality control programs. Therefore, when starting to use a new blood collection tube, assay interferences should be tested, especially for immunoassay systems.