Table 2. Concentrations of Triiodothyronine (T3), Thyroxine (T4), Free T3, and Free T4 Across the Study Assay Systems.
| Biotin Use | Mean of Analyte Concentrations (95% CI) | Mean of Day 7 Difference From the Mean of Baseline and Day 14 (95% CI)a | Day 7 Difference P Value | Mean of Analyte Concentrations (95% CI) | Mean of Day 7 Difference From the Mean of Baseline and Day 14 (95% CI)a | Day 7 Difference P Value | |
|---|---|---|---|---|---|---|---|
| Total T4, µg/dL | Free T4, ng/dL | ||||||
| cobas | |||||||
| Baseline | Without | 6.93 (6.19 to 7.68) | 0.19 (−0.17 to 0.55) | .32 | 1.25 (1.09 to 1.41) | 0.13 (0.05 to 0.20) | .01 |
| Day 7 | With | 7.03 (6.15 to 7.91) | 1.37 (1.24 to 1.49) | ||||
| Day 14 | Without | 6.75 (6.21 to 7.29) | 1.23 (1.09 to 1.38) | ||||
| Vitros | |||||||
| Baseline | Without | 6.88 (6.07 to 7.69) | 0.06 (−0.32 to 0.44) | .77 | 1.19 (1.09 to 1.29) | 0.04 (−0.03 to 0.10) | .29 |
| Day 7 | With | 6.85 (5.85 to 7.84) | 1.21 (1.12 to 1.30) | ||||
| Day 14 | Without | 6.69 (6.11 to 7.28) | 1.16 (1.06 to 1.25) | ||||
| Vista | |||||||
| Baseline | Without | 7.57 (6.60 to 8.54) | –0.03 (–0.44 to 0.38) | .90 | 1.00 (0.92 to 1.07) | 0.02 (–0.02 to 0.06) | .31 |
| Day 7 | With | 7.33 (6.30 to 8.35) | 1.01 (0.95 to 1.07) | ||||
| Day 14 | Without | 7.14 (6.36 to 7.91) | 0.98 (0.92 to 1.03) | ||||
| Architect | |||||||
| Baseline | Without | 5.12 (4.59 to 4.65) | 0.02 (–0.25 to 0.28) | .90 | 0.95 (0.90 to 1.0) | 0.02 (–0.02 to 0.06) | .37 |
| Day 7 | With | 5.10 (4.55 to 5.64) | 0.97 (0.92 to 1.01) | ||||
| Day 14 | Without | 5.05 (4.64 to 5.43) | 0.94 (0.90 to 0.99) | ||||
| Total T3, ng/mL | Free T3, pg/mL | ||||||
| cobas | |||||||
| Baseline | Without | 1.02 (0.88 to 1.16) | 0.85 (0.49 to 1.22) | .001 | 3.22 (2.87 to 3.56) | 0.36 (0.17 to 0.55) | .005 |
| Day 7 | With | 1.87 (1.08 to 2.65) | 3.57 (3.22 to 3.92) | ||||
| Day 14 | Without | 1.01 (0.90 to 1.12) | 3.20 (2.82 to 3.58) | ||||
| Vitros | |||||||
| Baseline | Without | 1.21 (1.14 to 1.28) | 0.04 (–0.002 to 0.08) | .10 | |||
| Day 7 | With | 1.25 (1.14 to 1.36) | |||||
| Day 14 | Without | 1.21 (1.14 to 1.28) | |||||
| Centaur | |||||||
| Baseline | Without | 1.04 (0.92 to 1.15) | 0.04 (–0.01 to 0.09) | .18 | |||
| Day 7 | With | 1.08 (0.92 to 1.25) | |||||
| Day 14 | Without | 1.05 (0.93 to 1.17) | |||||
| Architect | |||||||
| Baseline | Without | 0.96 (0.85 to 1.06) | 0.04 (–0.01 to 0.09) | .18 | |||
| Day 7 | With | 0.99 (0.87 to 1.11) | |||||
| Day 14 | Without | 0.95 (0.84 to 1.06) | |||||
| Vista | |||||||
| Baseline | Without | 2.74 (2.47 to 3.01) | 0.78 (0.50 to 1.06) | <.001 | |||
| Day 7 | With | 3.51 (2.94 to 4.07) | |||||
| Day 14 | Without | 2.71 (2.39 to 3.03) | |||||
Abbreviations: See Figure legends for full names of the assay systems.
SI conversion factors: To convert total T3 from ng/mL to nmol/L, multiply by 1.54; total T4 from µg/dL to nmol/L, multiply by 12.871; free T3 from pg/mL to pmol/L, multiply by 1.54; free T4 from ng/dL to pmol/L, multiply by 12.871.
Each analysis was a repeated measures of analysis of variance (ANOVA; mixed linear model), for which the random effect was a participant and the within-participant fixed effect was the study day. The primary comparison was study 7 vs the mean of the baseline and study day 14 measures using a contrast in the ANOVA, ie: study day 7 −(½ baseline + day 14). Data are presented as the absolute mean difference of day 7 from the mean of baseline and day 14 (95% CI). The units for the day 7 difference are the same as those of analyte concentrations.