Influence of seasonal variations in ambient temperatures on performance of immunochemical faecal occult blood test for colorectal cancer screening: observational study from the Florence district Grazia Grazzini, 1 Leonardo Ventura, 2 Marco Zappa, 2 Stefano Ciatto, 1 Massimo Confortini, 3 Stefano Rapi, 4 Tiziana Rubeca, 3 Carmen Beatriz Visioli, 2 Stephen P Halloran 5 ABSTRACT Background Faecal occult blood testing (FOBT) in population screening has proved to be effective in reducing mortality from colorectal cancer. In Italy a latex agglutination FOBT has been adopted for a single-sample screening programme. The aim of this study was to examine the performance of FOBTs in the Florence screening programme over several seasons to evaluate the impact of variations in ambient temperature on the performance of the screening test. Methods Measured haemoglobin (Hb) concentrations were aggregated into seasons with their average ambient temperature (AAT). Using logistic regression, the AAT over the period preceding the test measurement was analysed. This period included the time between faecal sampling and return of the test sample (mean 7 days) and the time in the laboratory refrigerator before analysis (mean 4 days). The AAT from days 5e11 before analysis of the test sample was considered a determinant of test positivity. The KruskaleWallis rank test was used to evaluate the significance of seasonal and/or AAT-related differences in Hb concentration. A logistic regression model adjusted for sex, age, season and screening episode (first or repeated examination) was constructed. Results 199 654 FOBT results were examined. Mean FOBT seasonal Hb concentrations (ng/ml) were: spring 27.6 (95% CI 26.2 to 29.1); summer 25.2 (95% CI 23.1 to 27.3); autumn 29.2 (95% CI 27.7 to 30.6); winter 29.5 (95% CI 27.9 to 31.1). Logistic regression showed that there was a 17% lower probability of the FOBT being positive in summer than in winter. The results of the logistic regression showed that an increase in temperature of 18C produced a 0.7% reduction in probability of a FOBT being positive. In the summer the probability of detecting a cancer or an advanced adenoma was about 13% lower than in the winter. Conclusions This study showed that there is a significant fall in Hb concentration at higher ambient temperatures. These results will have important implications for the organisation of immunochemical FOBT-based screening programmes, particularly in countries with high ambient temperatures. BACKGROUND Screening by faecal occult blood testing (FOBT) has proved to be effective in decreasing mortality from Significance of this study What is already known about this subject? < Haemoglobin (Hb) is not stable in faeces. High moisture levels can reduce stability and impair the performance of dry collection guaiac-based faecal occult blood tests (gFOBTs) such as Hemoccult. In the wet collection systems used by most immunochemical FOBTs (iFOBTs), globin (the measured component of Hb in these tests) is even more susceptible to denaturation than haem. < Although iFOBTs are gradually replacing gFOBTs as the test of choice for screening, little is known about their stability under the range of storage conditions which occurs in population- based screening programmes where environ- mental conditions cannot be easily controlled. < A recent study has described the occurrence of false negative iFOBTs with delayed return of the test sample. What are the new findings? < This study is the first to describe a relationship between the seasons and the Hb concentrations measured in faecal samples in a screening programme for colorectal cancer. < The results show a significant difference in the proportion of iFOBT positive results in the summer than in the winter, a difference which is likely to be related to ambient temperature differences. < In the summer the probability of detecting a neoplastic lesion is about 13% lower than in the winter. How might seasonal variations have an impact on clinical practice? < During the summer, significant neoplasia will be missed which will increase the number of interval cancers. < These observations have significant implications for the organisation of national screening programmes. New mechanisms will need to be considered which will minimise the effect of seasonal temperature variations on positive rates. See Commentary, p 1451 1 Screening Department, Cancer Prevention and Research Institute (ISPO), Florence, Italy 2 Clinical and Descriptive Epidemiology Department, Cancer Prevention and Research Institute (ISPO), Florence, Italy 3 Bio-molecular and Analytical Cytology Laboratory, Cancer Prevention and Research Institute (ISPO), Florence, Italy 4 General Laboratory, Careggi Hospital, Florence, Italy 5 Bowel Cancer Screening Southern Programme Hub, Postgraduate Medical School, University of Surrey, Guildford, Surrey, UK Correspondence to Grazia Grazzini, Department of Screening, ISPO Cancer Prevention and Research Institute, Viale A Volta 171, 50131 Firenze, Italy; g.grazzini@ispo.toscana.it Received 9 November 2009 Accepted 16 April 2010 Published Online First 5 July 2010 Gut 2010;59:1511e1515. doi:10.1136/gut.2009.200873 1511 Colon cancer