Table 3

 Comparison of the relative performance of I-FOBT versus G-FOBT, according to the positivity level of I-FOBT

Positivity threshold (I-FOBT ng/ml)Positivity rate (%)*Adenoma ⩾10 mm or high grade dysplasia (RSN†)Colorectal cancerAdvanced neoplasia (colorectal cancer or adenoma⩾10 mm or high grade dysplasia)
G-FOBT, guaiac faecal occult blood test; I-FOBT, immunochemical faecal occult blood test; PPV, predictive positive value; RFP, ratio of false positive rate; RSN, ratio of sensitivity.
Values for RSN, RFP and FP:TP are mean [95% confidence interval].
*Patients with both analysable tests, independent of whether or not a colonoscopy was performed or not (n = 887).
†RSN>1, sensitivity of I-FOBT is greater than that of G-FOBT.
‡RFP>1, false positive rate of I-FOBT is greater than that of G-FOBT, the specificity of I-FOBT is therefore inferior to G-FOBT.
§FP:TP, number of extra false positives associated with the detection of one extra true disease case using I-FOBT instead of G-FOBT.
I-FOBT20 ng/ml6.93.56 [2.66–4.77]4.01.50 [1.11–2.03]2.88 [2.46–3.36]47.43 [22.32–100.80]30.23.02 [2.38–3.84]2.68 [2.24–3.22]2.17 [1.65–2.85]
50 ng/ml3.32.08 [1.63–2.64]7.71.36 [0.99–1.87]1.28 [1.08–1.53]10.00 [2.86–34.97]44.72.33 [1.73–3.14]0.99 [0.79-1.23]
75 ng/ml2.41.70 [1.33–2.16]8.71.14 [0.83–1.58]0.94 [0.78–1.14]49.21.90 [1.41–2.56]0.67 [0.53–0.86]