Effect of season and ambient temperature on outcome of guaiac-based faecal occult blood tests performed for colorectal cancer screening

Aim Guaiac-based faecal occult blood tests (gFOBTs) are used in the colorectal cancer screening programme. Recent data suggested that the immunological faecal occult blood test illustrated a variation in positivity according to season and ambient temperature. Our aim was to assess the effect of season and ambient temperature on the positivity rates of the gFOBT during pilot screening for colorectal cancer. Method Data from the first year of round 1 of the pilot screening programme in Coventry and Warwickshire were analysed. Patients with positive and negative gFOBT samples were included. Patients with spoilt samples or incomplete data were excluded. Of the total of 59 513 patients, 30 311 were men and 29 202 women. Mean age was 56 years. Daily temperature data were provided by the meteorological office. Results Median exposure of the gFOBT test card was 6 days (range 117). Median daily maximum temperature was 14 degrees C. Spring and summer illustrated significantly decreased positivity rates compared with autumn and winter (Pearsons chi-squared test, P < 0.001). Mean daily maximum temperature for the test card exposure showed no significant difference in positivity rates (P = 0.53). Subgroup analysis revealed a significant reduction in positive samples in the > 25 degrees C subgroup (P = 0.045). Conclusions There is a seasonal variation in positivity rates of gFOBTs with increased positivity in spring and summer months. There is no difference in positivity rates in relation to ambient temperature except in subgroup analysis where there is a significant reduction in positivity rates above 25 degrees C.