I remember learning in medical school about what a screening test is and the factors necessary to make a 'good' screening test.
The disease in question should:
- constitute a significant public health problem, meaning that it is a common condition with significant morbidity and mortality.
- have a readily available treatment with a potential for cure that increases with early detection.
The test for the disease must:
- be capable of detecting a high proportion of disease in its preclinical state
- be safe to administer
- be reasonable in cost
- lead to demonstrated improved health outcomes
- be widely available, as must the interventions that follow a positive result
(American Medical Association Council on Scientific Affairs. Commercialized Medical Screening (Report A-03). no longer available online, but cited on Virtual Mentor)
We have obviously lost our way!!
In medical school I was excited about ensuring every patient got ALL THE SCREENING! I never thought I'd struggle to justify a screening test.
These days, I would be hard-pressed today to confidently name you one "good" screening test. Maybe paps? Maybe colonoscopies? I follow my jurisdiction's guidelines. I discuss the risks and benefits of screening with patients because I'm not certain that what we are doing is definitely "good."
It's hard to summarize it any more clearly than this:
Among currently available screening tests for diseases where death is a common outcome, reductions in disease-specific mortality are uncommon and reductions in all-cause mortality are very rare or non-existent.
A paper in the International Journal of Epidemiology from June 2014 that just came to my attention recently draws this conclusion.
The authors looked at data from 48 Randomized Controlled Trials (RCTs) and 9 meta-analysis on the subject of screening tests (39 of them) for 19 potentially deadly diseases. The studies they included regarded things like mammography for breast cancer, echocardiography for heart disease, PSAs for prostate cancer, and so on.
Some limitations are acknowledged but I also wonder if there is another. For very worthwhile "common sense" things (if these things exist, and I'm not saying they do!) there is little published data. For example, the efficacy of the newborn screening exam or GBS screening in pregnancy don't seem to have been thoroughly studied but are considered to be "law, written in stone" in practice. For the more controversial screening tests, there are more trials published, and so that might weight this meta-analysis towards saying that screening tests on the whole are not useful. I actually think the conclusion the their analysis is appropriate, as the closer we look at other "written in stone" practices, the more we realize we were wrong!
This sentence in the discussion of the article I think sums up the complex nature of the results really well:
There are many potential underlying reasons for the overall poor performance of screening in reducing mortality: the screening test may lack sufficient sensitivity and specificity to capture the disease early in its process; there are no markedly effective treatment options for the disease; treatments are available but the risk-benefit ratio of the whole screening and treatment process is unfavourable; or competing causes of death do not allow us to see a net benefit. Often, these reasons may coexist. Whether screening saves lives can only be reliably proven with RCTs.
See for yourself! Read the full article.