Bowel cancer screening test 'may be less accurate in summer'
A new study suggests that the test used in the Italian national bowel cancer screening programme may be less likely to spot cancerous changes in summer than it is in winter.
The study looked at the 'immunochemical' faecal occult blood test (iFOBT). The test detects traces of blood in participants' stool samples, which may be a sign that an individual has bowel cancer or precancerous changes in their gut.
In the UK the national bowel screening programmes use a different, older version of the test, called gFOBT (guaiac faecal occult blood test). Samples taken using gFOBT deteriorate less quickly than those taken using iFOBT.
Scientists at the Cancer Prevention and Research Institute in Florence, Italy, analysed how ambient temperatures affected the performance of the iFOBT in the Italian national screening programme in Florence.
They studied temperature variations during the time between sampling and the return of test samples to the lab - estimated to be around seven days - and the time spent in a refrigerator in the lab - about four days - for just under 200,000 iFOBT results.
Analysis revealed that levels of haemoglobin - the protein that gives blood its red colour - were significantly lower in the summer months. This is thought to be because haemoglobin degrades more quickly at higher temperatures.
The likelihood of a test being positive for signs of blood was 17 per cent lower in the summer than in the winter, dropping by 0.7 per cent for every one degree rise in temperature.
The chances of the test picking up an established cancer or precancerous changes were estimated to be about 13 per cent lower in summer than in winter.
Writing in the journal Gut, the study authors claimed that the findings could have implications for 'interval cancers' - tumours that develop between screenings.
"During the summer, significant neoplasia [cancerous changes] will be missed, which will increase the number of interval cancers," they warned.
"Our observations have important implications for the organisation of iFOBT-based screening programmes. [These] are greatest for those countries with wide seasonally related temperature variations."
Sarah Woolnough, head of policy at Cancer Research UK, said: "While this study looks at the Italian bowel screening programme, the recommendations may help improve the accuracy of the current bowel cancer screening programme.
"Earlier this year a new screening test called 'Flexi-scope' was shown to reduce the risk of developing bowel cancer by a third. We are calling on the government to add this to the current screening programme which could save thousands of lives a year."
- Grazzini, G., Ventura, L., Zappa, M., Ciatto, S., Confortini, M., Rapi, S., Rubeca, T., Visioli, C., & Halloran, S. (2010). 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 Gut DOI: 10.1136/gut.2009.200873