Table 1 Summary of the distribution of the ferritin levels from the Abbott ARCHITECT and Ortho-Clinical Diagnostics Vitros 7600 assay platforms, comparison for the methods by the Passing-Bablok and Deming regression procedures and assessment of the agreement between the two methods by the Bland–Altman plot analysis

Number of samples, N

N = 111

N = 68

N = 179

ABBOTT ARCHITECT i1000

 Mean ferritin level (µg/L)

1051.6

1190.3

1104.2

 Standard Deviation

734.5

641.4

702

 Skewness

0.41

-0.21

0.2

 Kurtosis

3.02

2.38

2.78

 Median Ferritin level (µg/L)

1171

1180.5

1171

 IQR

343.6–1497.8

827.5–1628.5

510–1535

ORTHO-CLINICAL DIAGNOSTICS VITROS

 Mean ferritin level (µg/L)

650.9

726.7

679.7

 Standard Deviation

469.8

385

439.9

 Skewness

0.54

-0.18

0.31

 Kurtosis

3.26

2.63

3.1

Median Ferritin level (µg/L)

705

763.5

731

 IQR

227–906

560.5–921.5

285–908

METHODS COMPARISON

 Passing-Bablok regression^a

  Intercept (95% CI)

-3.9 (9.56 to -0.18)

13.07 (-4.69 to 36.9)

-1.17 (-6.78 to 4.6)

  Slope (95% CI)

0.63 (0.61 to 0.64)

0.59 (0.56 to 0.63)

0.62 (0.60 to 0.63)

  Percentage difference ((95% CI)

37 (36 to 39)

41 (37 to 44)

38 (37 to 40)

Deming regression^a

 Intercept ((95% CI)

-17.59 (-34.64 to -0.53)

20.74 (-2.12 to 43.6)

-6.86 (-20.91 to 7.19)

 Slope (95% CI)

0.64 (0.61 to 0.66)

0.59 (0.56 to 0.62)

0.62 (0.60 to 0.64)

 Percentage difference (95% CI)

36 (34 to 39)

41 (38 to 44)

38 (36 to 40)

Bland Altman

 Lower limit of agreement (%) (95% CI)

-73.75 (-77.76 to -69.54)

-66.93 (-71 to -62.85)

-71.23(-74.19 to -68.27)

 Upper limit of agreement (%) (95% CI)

-24.21 (-28.32 to -20.1)

-28.79 (-32.87 to -24.71)

-25.82 (-28.78 to -22.86)

 Percentage bias (95% CI)

-48.9 (-51.3 to -46.6)

-47.9 (-50.21 to -45.5)

-48.5 (-50.2 to -46.8)

 Percentage Standard deviation of the bias

12.6

9.7

11.6