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.