Screen Tests: The Dilemmas of Predicting Diseases

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In 1985, the first HIV test came on the market. It was a crucial moment in the fight against AIDS, and a turning point for medicine as a whole. For the first time, doctors could tell healthy people-who weren’t showing any symptoms-if they were going to get sick. And for the first time, patients had to ask if the benefits of knowing outweighed the emotional and social risks of ignorance. That question soon grew far beyond HIV, as the Human Gen­ome Project-an international research initiative that successfully mapped out a blueprint of human DNA-increased the number of screening tests available, which now total more than 2,000. Today, people at high risk of breast and colon cancers, inherited heart disease and Huntington’s disease, among others, have the chance to glimpse their future health. But first they have to decide: do I really want to know?

The moral, ethical and legal questions surrounding screening are growing more complex as more tests become available. At-home kits that cost as little as $109 predict your likelihood of getting heart disease, cancer, arthritis and other illnesses. But studies have shown them to be unreliable. Timothy Caulfield, health law and policy professor at the University of Alberta, took one of the tests while researching a book. “I found out nothing of value,” he says. “You find out you’re at a slightly increased risk for heart disease. What do you do with that information? Get exercise, eat lots of fruits and vegetables-everything we’re supposed to do anyway.”

In most provinces, you’ll need a referral to receive a doctor-administered test. For breast cancer, the gen­etic mutation tested for causes five to 10 per cent of cases; as such, the tests are generally offered only  to people with a family history of the illness. Of the patients identified as high risk, many will opt to take the test, says Allison Hazell, genetic counsellor at Toronto’s Medcan Clinic. “If you know there’s a risk, it can be really liberating to learn you don’t carry the gene,” she says. 

Positive results mean people can take steps to protect themselves. Surgery, like a prophylactic mastectomy, is one option. Another is amped-up screening, such as mammograms starting at age 30. Results can also be useful information for siblings or children, who may have an increased risk. Last year, Angelina Jolie became a flashpoint for the process when the actor revealed she tested positive for the BRCA1 gene and had a preventative double mastectomy as a result. But for others, the fear of a positive test result will win out. “We’re told knowledge is power,” says Michael Burgess, health professor at the University of British Columbia. “It isn’t always.”

People with a family history of Huntington’s disease have a harder decision to make, since there are no effective treatments. The test is 100 per cent accurate at predicting the debilitating neurodegenerative disorder. When one University of British Columbia study asked people in the Vancouver area if they would take the test, only 20 per cent said yes. 

In the meantime, researchers continue to seek biomarkers for individual diseases. In March, scientists published a study identifying 10 biomarkers that could predict the onset of Alzheimer’s. Another study, published in February, found that high levels of certain molecules in your bloodstream could determine your chances of dying within the next few years. That, however, might be too much information. 

Ask an Expert: How to Prepare for a Genetic Test

Consider how your life could change. ”Think about the implications for yourself,” says Allison Hazell, genetic counsellor at Toronto’s Medcan Clinic. “Knowing this information, would you do anything differently?” Contemplate whether you’d have surgery or more frequent screenings if you’re at a higher risk.

Evaluate your capacity for bad news. Ask yourself whether you’re able to emotionally handle a positive result. For some, Hazell says, the anxiety is overwhelming. Think about how you’ll tell family members, and how it would affect planning for the future, especially if you’re a parent. “Once you have the information, you can’t go back to unknowing it,” Hazell says.

Get your insurance in order. Think about practical issues: in Canada, insurance companies can reject health, life and disability insurance because of test results. Counsellors often advise people to have insurance in place before their tests, Hazell says. 

The Breakthrough

Researchers in the United States are one step closer to a blood test that predicts Alzheimer’s disease. The scientists’ study, published in the April issue of Nature Medicine, discovered a set of biomarkers in the blood that indicates mild cognitive impairment and Alzheimer’s before symptoms appear. The hope is that it will lead to a test that can show, with more than 90 per cent accuracy, who has the disease and will experience symptoms within three years. That way, current medications will be more effective if they’re used before symptoms start to show. “It’s almost like a house on fire,” says Mark Mapstone, the lead author of the study. “We want to get to the house before it’s engulfed in flames, when the fire’s in the trash can in the kitchen, so we can put it out.”