Table 3. Comparison data of four carcinoembryonic antigen (CEA) immunoassays using 355 serum samples with CEA<100 ng/mL.

Statistics	Centaur XP (y) vs i2000sr (x)	Centaur XP (y) vs E170 (x)	Centaur XP (y) vs DxI800 (x)	i2000sr (y) vs E170 (x)	i2000sr (y) vs DxI800 (x)	E170 (y) vs DxI800
Passing-Bablok regression
Regression equation	y=−0.629+0.628x	y=−0.377+0.671x	y=−0.038+0.709x	y=0.665+1.038x	y=1.214+1.114x	y=0.557+1.045x
Intercept (95% CI)	−0.910 to −0.386	−0.595 to −0.181	−0.199 to 0.104	0.269 to 1.048	0.640 to 1.727	0.240 to 0.904
Slope B (95% CI)	0.597 to 0.657	0.648 to 0.693	0.691 to 0.729	0.996 to 1.074	1.049 to 1.175	1.002 to 1.085
Cusum test for linearity	ns (P=0.97)	ns (P=0.88)	ns (P=0.20)	ns (P=0.31)	ns (P=0.46)	ns (P=0.38)
Bland-Altman analysis
Mean difference (ng/mL) (95% CI)	−8.1 (−9.1 to −7.2)	−6.5 (−7.2 to −5.7)	−5.1 (−6.0 to −4.3)	1.6 (1.1 to 2.2)	3.0 (2.2 to 3.8)	1.3 (0.6 to 2.1)
P value	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	0.0003

Abbreviations: y, y axis; x, x axis; 95% CI, 95% confidence interval.