Doing any test is not better than doing no test

Murray’s letter repeats a common mistake in thinking about screening, that “doing any test is better than doing nothing at all.”1 In fact, sometimes doing nothing is better than doing something: more is not always better.2

There are risks and harms with all medical interventions including screening.3 It is imperative not only that cancer screening programs find malignancies early but also that they yield more benefit that harm: harm generally arises from false-negative results, false-positive results and overdiagnosis.4

Although the risk of a false-negative result may be mitigated by repeat screening, it may also lead to harm.4 A person falsely reassured may continue an unhealthy lifestyle and be less likely to return for repeat screening.5 A false-positive result often leads to a cascade of increasingly invasive medical interventions, as well as the psychological distress of becoming a patient and being labeled as “ill.”4^,5

Specific to colonoscopy are a number of risks. Murray correctly states that a 1:1000 risk of perforation is rare,1 but rare events add up quickly when numerous people are screened. With millions of Canadians eligible for colon cancer screening, rare risks are not negligible.6

It is true that people with “symptoms … will need to be investigated.”1 However, these people are not being screened.6 Screening is meant to catch disease early and is carried out on apparently well asymptomatic people. Though the current evidence does not support the use of colonoscopy for population-based primary screening — hence, colonoscopy is not recommended as a primary population screening test6 — colonoscopy does have other roles in health care.