Understanding How Screening Recommendations Are Made

For starters, let’s discuss preventive medicine. The main purposes of preventive medicine are the following:

1. Try to prevent diseases from occurring in the first place (primary prevention). An example of this is vaccination.
2. Detect diseases early and treat them (secondary prevention). A good example of this is screening for cancer, which has the goal of detecting precursors to cancer or early cancer. This can improve the prognosis.
3. Prevent progression of the disease once it is established (tertiary prevention). An example of this would be taking certain medications after a heart attack, to prevent complications that can happen afterwards.

"A little understanding goes a long way, and the more informed patients are about their screening options, the better."

For the purposes of this article, we will be focusing on screening tests. When patients want to know about the best way to screen for diseases such as cancer, many would like a “black and white“ answer. Indeed, since the goal of screening recommendations is to improve general public health, it would be nice if there was a “one-size-fits-all“ solution to screening… but unfortunately that’s not the case. Recommendations for public health screenings are designed to make the most substantial impact for the largest number of people. Despite this, most screening recommendations still have to be catered to the individual. In order to do this properly, patients need to be actively involved in this process. A little understanding goes a long way, and the more informed patients are about their screening options, the better. 

If you envision the “perfect" cancer screening test, it would be:

1. Safe, easy, and inexpensive.
2. It would never miss detecting a cancer when you do have it.
3. It would never indicate that you have cancer when you don’t have it.
4. It would be meaningful. You would be able to treat it / do something about it if you did find it.

Unfortunately, in the real world, there is no test that meets all of these criteria. Those are nonetheless the four main factors that are considered and hopefully optimized when experts make recommendations for screening tests. The goal is to minimize the risks of screening, optimize the benefits, and keep it as simple and free from unpleasant side effects as possible. Also, the more cost-effective the better.

There ideally should be as few false negatives and false positives as possible. Let’s look into this concept a little deeper, and talk a little about sensitivity and specificity of screening tests. 

Let’s imagine there was a blood test that could detect early brain cancer. When we screen an imaginary 1000 people for the disease, we come up with these imaginary numbers:

-125 test positive for the disease. 100 actually have the disease, 25 don’t.

-875 test negative for the disease. 100 actually have the disease, 775 don’t. 

That gives us something that looks like this:

To determine the sensitivity of the test, the calculation is to divide the number of true positives by the total number of people with the disease (true positives + false negatives). In this case, it is 100 / 200, or 50%. 

To determine the specificity of the test, the calculation is to divide the number of true negatives by the total number of people without the disease (true negatives + false positives). In this case, it is 775 / 800, or 97%. 

In short, sensitivity and specificity are measures of the effectiveness of a test. These factors are strongly taken into consideration when making screening recommendations for the public. 

Lastly, the test needs to be meaningful. There’s no point in running a test if it doesn’t improve the treatment effectiveness for the condition being screened. If there’s no benefit to finding a disease early, then there’s no point in running a screening test.

All of these factors are considered in the context of their impact on public health when recommendations for screening are made. The medical societies that make these recommendations try to balance everything, to minimize risks and optimize benefits. The scientific process that takes place to evaluate screenings is meticulous and data-driven, but the art of making the actual recommendations is definitely an imperfect science. It’s a balancing act, somewhere in the gray area between benefit and risk. 

Sometimes you have to “rob Peter to pay Paul”, so to speak. These aren’t easy decisions to make, because you’re trying to balance between recommending a test that could potentially cause harm to an individual versus potentially missing a cancer in the early stages. Then to complicate things further, age, race, genetics, gender, safety, and cost must all be factored in.

As you can see, there is rarely a clear “black-and-white” answer. But the societies that make these recommendations have reasons for them, and they are usually transparent with what leads them to make their recommendations. It’s just complicated. 

That’s why this website was created. Hopefully the information provided here will clearly lay out the recommendations and options, make it easier to understand, and help patients make more educated decisions.

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