More accurate alternatives to serum creatinine for evaluating glomerular filtration rate.

sured FT3 by Immulite 2000 and ACS 180 plus (Bayer Corporation), as an alternative instrument, and triiodothyronine (T3) only by Immulite 2000 (Table 1). A significant group effect was shown by repeated-measures ANOVA in SST results obtained by Immulite 2000 and ACS 180 plus (F 107.25; P 0.001). T3 values gradually increased in both types of tubes with time, and repeated-measures ANOVA showed a significant time effect (F 8.450; P 0.001). Additionally, we compared two types of evacuated gel-containing tubes, Vacutainer (SST) and Vacuette (16 100 mm; Greiner) for FT3 on the Immulite 2000 (n 6). FT3 was higher in the SSTs than in the Vacuettes (Table 1). A significant group effect was shown by repeated-measures ANOVA (F 4.320; P 0.044). Finally, to determine the magnitude of the effect of relatively shortterm storage at room temperature on FT3, we measured FT3 by Immulite 2000 at 4-h intervals up to 12 h. Repeated-measures ANOVA showed a significant group effect (F 34.809; P 0.001) but not a significant time effect or group–time interaction (P 0.05). Although the mechanism of the FT3 increase remains unresolved, the following mechanisms could be envisioned: (a) in gel-containing tubes, the barrier gel could displace FT3 from binding proteins such as thyroxine-binding globulin, albumin, and transthyretin; (b) the barrier gel could enhance binding of labeled analog to binding proteins; and (c) the barrier gel could show FT3-like activity or interfere with the indicator chemiluminescent reaction under assay conditions.