Background: Increased total triiodothyronine (TT 3 ) assay results in apparently euthyroid patients triggered an investigation of the effect of blood collection tubes on serum TT 3 and other laboratory assays. Methods: We examined potential assay interference for three types of tubes: plastic Greiner Bio-One

Background: A small number of immunoassays on several different types of analyzers were recently adversely affected by tube additives in Becton Dickinson (BD) Vacutainer® SST™, SST II, and Microtainer™ blood collection tubes. We examined the effect of a commonly used tube surfactant, Silwet™ L-720, on immunoassays and the mechanism for the interference. Methods: Immunoassays were performed on serum supplemented with Silwet L-720 on the IMMULITE™ 2500 and AxSYM™ analyzers. Direct effects of the surfactant on the chemiluminescent detection step of immunoassays and on antibody immobilization on the solid phase were examined. Results: Increasing the final surfactant concentration from 0 to 400 mg/L in serum significantly increased (∼51%) the apparent total triiodothyronine (TT3) concentrations measured on the IMMULITE 2500 but not the AxSYM analyzer. Several other competitive, but not noncompetitive, assays were also significantly affected by the surfactant on the IMMULITE 2500 analyzer. The effect was independent of serum components, and the surfactant had no direct effect on chemiluminescence reactions. The capture antibody, however, was displaced from the solid phase by incubation with solutions containing surfactant under conditions similar to the IMMULITE TT3 assay. Conclusions: The Silwet L-720 surfactant, which is used to coat the inner surfaces of tubes, appears to account for previously reported immunoassay interference by BD Vacutainer SST blood collection tubes. One of the mechanisms for the interference is the desorption of antibodies from the solid phase by the surfactant. The results identify an important factor in the selection of suitable blood collection tube surfactants and provide an approach for solving similar tube-assay interference problems in the future.

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Oversulfated chrondroitin sulfate (OSCS) was recently identified as a contaminant of heparin and was associated with serious adverse events in patients treated with heparin. Because heparin is a common component of blood collection tubes, we tested the effect of OSCS on the laboratory analysis of plasma. Blood from healthy volunteers (N=50) was collected into tubes containing various mixtures of heparin and OSCS. Samples were inspected for microclots and were analyzed for a panel of 28 routine laboratory tests. No microclots were observed in tubes that contained only heparin but were detected in 18%, 88% and 76% of plasma samples containing 5%, 15%, 20% OSCS (%weight relative to heparin), respectively. OSCS at the highest dose (20%) caused a systematic bias for the following 6 tests: Lactate Dehydrogenase: 18% (12% to 24%); Triiodothyronine: -5.7% (-8.1% to -3.3%); Potassium: -2.8% (-4.2% to -1.4%); Total Protein: 2.5% (1.4% to 3.6%); Chloride: -1.4% (-1.8% to -1.0%) and Uric Acid: 1% (0.5% to 1.4%). In summary, OSCS contamination of heparin was found to potentially affect the anticoagulation of plasma and the analytical performance of several routine clinical laboratory tests.