Diagnostic Values of Free Triiodothyronine and Free Thyroxine and the Ratio of Free Triiodothyronine to Free Thyroxine in Thyrotoxicosis

Table 2

Diagnostic evaluation of cut-off levels of FT3, FT4, and FT3/FT4 ratio in untreated Graves’ disease.

	FT3 > 7.215 pmol/L	FT4 > 20.71 pmol/L	FT3/FT4 > 0.4056
PPV	122/140 (87.14%)	121/149 (81.21%)	109/113 (96.46%)
NPV	4/10 (10.00%)	5/31 (16.13%)	17/66 (25.76%)
Sensitivity	96.60%	96.60%	87.30%
Specificity	80.50%	72.70%	91.40%
AUC 95% CI	0.949 (0.925–0.973)	0.849 (0.852–0.935)	0.940 (0.912–0.969)

A receiver operating characteristic (ROC) curve analysis was performed to obtain the optimal cut-off values for FT3, FT4, and FT3/FT4 ratio for the diagnosis of GD. The sensitivity and specificity of FT3 and FT4 level and FT3/FT4 ratio were estimated from the ROC curves. The positive predictive values (PPVs) and negative predictive values (NPVs) from the ROC curves for FT3, FT4, and the FT3/FT4 ratio were also calculated and compared. PPV: positive predictive values; NPV: negative predictive values; AUC: area under the curve; 95% CI: 95% confidence interval.