Table 2. Correlation between TT4 and TSH.

		TSH			Log TSH
		Correlation (R)	95% CI	P	Correlation (R)	95% CI	P
TT4	ID-LC-MS/MS	−0.371	−0.516– −0.206	< 0.001	−0.743	−0.813– −0.651	< 0.001
	Abbott	−0.347	−0.496– −0.178	< 0.001	−0.777	−0.840– −0.694	< 0.001
	Autobio	−0.387	−0.530– −0.222	< 0.001	−0.778	−0.840– −0.695	< 0.001
	Beckman	−0.391	−0.534– −0.227	< 0.001	−0.738	−0.819– −0.643	< 0.001
	Mindray	−0.382	−0.524– −0.218	< 0.001	−0.771	−0.835– −0.687	< 0.001
	Roche	−0.389	−0.531– −0.226	< 0.001	−0.779	−0.841– −0.698	< 0.001
	Siemens	−0.394	−0.537– −0.229	< 0.001	−0.750	−0.820– −0.658	< 0.001

Abbreviations: TT4, total thyroxine; CI, confidence interval; ID-LC-MS/MS, isotope-diluted liquid chromatography-tandem mass spectrometry; TSH, thyroid stimulating hormone.