Effect of blood collection tubes on total triiodothyronine and other laboratory assays

Background: Increased total triiodothyronine (TT3) assay results in apparently euthyroid patients triggered an investigation of the effect of blood collection tubes on serum TT3 and other laboratory assays. Methods: We examined potential assay interference for three types of tubes: plastic Greiner Bio-One(TM) Vacuette(TM); glass Becton Dickinson (BD) Vacutainer(TM); and plastic BD Vacutainer SST(TM) tubes. Serum samples from apparently healthy volunteers (age range, 30-60 years; 15 males and 34 females) were collected in different tube types and analyzed in 17 immunoassays (n = 49), 30 clinical chemistry tests (n = 20), and 33 immunology assays (n = 15). Tube effects were also examined by adding pooled serum to different tube types. Results: TT3 values, when measured by the IMMULITE(TM) 2000 but not the AxSYM(TM) analyzer, were significantly higher (P < 0.0001) for SST (2.81 nmol/L) than either glass (2.15 nmol/L) or Vacuette (2.24 nmol/L) tubes. The effect was large enough to substantially shift the distribution of patient values, increasing the percentage of values above the reference interval from 11.3% to 35.8%. The degree of interference from SST tubes on TT3 differed among various tube lots and could be attributed to a tube additive shared by other plastic tubes. Results from several other tests statistically differed among tube types, but differences we're not considered to be clinically significant. Conclusions: Assay interferences from blood collection tubes represent challenges to clinical laboratories because they are not detected by the usual quality-control or proficiency testing programs. Laboratories can, however, address this problem by monitoring distribution of patients' results. (C) 2005 American Association for Clinical Chemistry.