Abstract
Symonds et al 1 found that higher faecal immunochemical test (FIT) positivity was independently associated with male sex, older age and lower socioeconomic status, and negatively associated with previous screening. High temperature at sample postage was associated with reduced positivity. For all variables, positivity was explicable by the faecal haemoglobin concentrations (f-Hb), determined by quantitative FIT.
These data confirm previous studies. An evaluation of FIT in Scotland 2 found that f-Hb was higher in men than women, and increased with age in both sexes. 3 At any cut-off f-Hb, more men and older people tested positive than women and younger people. Future risk of neoplasia was higher in men and older people. In Scotland, Taiwan and Italy, 4 f-Hb varied with age and sex, (though the degree of variation was inconsistent across countries), and at any cut-off f-Hb, more men and older people were positive than women and younger individuals. A study in Barcelona confirmed that f-Hb varies with age and sex inconsistently across countries. 5 In Scotland, as deprivation increased, f-Hb increased, even after controlling for age and sex. 6 In the Netherlands, at a single f-Hb cut-off of 10 µg/g, positivity was significantly higher among men (10.7%) than women (6.3%) in the first round; at the same cut-off, 6.8% of men and 4.8% of women were positive in the second round. 7 The f-Hb distributions by sex in both screening rounds clearly demonstrated why the found positivity results were obtained.
These studies, investigating f-Hb distributions by age, sex, and deprivation,2–6 along with supportive evidence1,7 and additional information on f-Hb distributions by temperature during specimen transport 1 and by screening round, 7 have shown that positivity can be fully explained by f-Hb.
Positivity rate is a surrogate marker for f-Hb. 6 Any factor affecting positivity, including age, sex, deprivation, previous screening exposures, analytical method (as all FIT are not the same) and other factors, such as ethnic group, will be reflected in the f-Hb in the relevant group. 6
In a number of countries, including The Netherlands, colorectal cancer (CRC) screening programmes have encountered higher than expected positivity, leading to overwhelming demands on scarce colonoscopy resources and a need to increase the f-Hb cut-off to lower referrals. 8 The programme initially invited older groups: analysis of the data showed that the positivity rate was related to participants’ years of birth. 8 The f-Hb distributions in pilot studies would have shown that f-Hb was higher in older than younger people and that therefore positivity would be higher in the initially invited screening group.
Consideration should be given to the following recommendations for CRC programme organizers.
Examine the f-Hb distributions in pilot participants, or very early in the programme, by age and sex. Determine positivity at different f-Hb cut-off(s) by age and sex. Assess the characteristics of the invited population in determining the f-Hb cut-off(s) to be used to obtain the positivity required. Change the f-Hb cut-off(s) where necessary, using the f-Hb distributions to set these objectively. Use examination of the f-Hb to investigate problems. Perform this assessment regularly as the programme evolves.