What Can I Do To Keep Myself Healthy?
by Alan Kronhaus, M.D.

The choices we make about the way we live are important to our health. The Health & Wellness section of Boom! is committed to becoming a source of reliable, evidence-based information that people can use to make good decisions about their healthcare services and lifestyles choices. There is no easily available source of such information in the Triangle today.

This month’s section is devoted to screening tests. Screening is a key strategy in the battle to prevent disease. Screening tests are used to find out which people in the population have a disease or condition. They get lots of media attention because they affect everyone, and because many screening tests are controversial.

Everyone knows they’re supposed to have certain tests done periodically, but there is considerable confusion about which tests are really worth doing, when to start doing them, and how often to do them. People waste time and money doing unhelpful tests, and don’t do some tests that are really worth doing.

The tests we’re talking about are the ones that screen for high blood pressure, diabetes, lipid disorders, atherosclerotic arterial disease, dementia, depression, and cancer of breast, cervix, colon, and prostate, as well as certain infectious diseases like HIV.

So, which tests are worth doing, and how often should we be doing them? Let’s start the discussion by talking about screening tests in general.

Screening tests are used to prevent disease by identifying individuals at risk for developing a disease before it becomes symptomatic. We determine who is “at risk” based primarily on their age and gender, but sometimes based on other considerations. 

By contrast, diagnostic tests are used to investigate symptoms a patient already has. Screening tests are applied to large groups of asymptomatic people. Diagnostic tests are applied to individual patients – people who see a doctor because something is bothering them.

To be considered worthwhile, screening tests must meet many important criteria. If a test fails to meet any of those criteria, it is of little value. A good screening test must:

• screen for a disease which has serious consequences, a long asymptomatic phase, and effective treatment;
  
• have high sensitivity and specificity (more on that below);
  
• be low in cost and acceptible to patients

These criteria make sense. No matter how good a test might be it is useless for screening purposes if people refuse to take it, or if it is prohibitively expensive, or if it brings to light a problem we can’t do anything about. 

“Sensitivity” and “specificity” are also important characteristics of a good screening test. Tests that are highly sensitive are used to exclude or “rule out” a diagnosis. They produce very few false negatives, meaning that if you test negative, you can be sure you don’t have the disease

Tests that are highly specific are used to establish a diagnosis. They produce few false positives, meaning that if you test positive, you can be sure you do have the disease.

To be recommended for widespread use, screening tests must be both highly sensitive and highly specific, which is a tall order. When they’re negative, you want to be able to breathe easy and go on with your life. When they’re positive, you want to be certain that further evaluation or treatment is warranted.

With all that in mind, let’s go back to our question: which tests should we be doing, and how often?  Fortunately, we can turn to real experts for advice.

The U. S. Preventive Services Task Force – we’ll call them the “Task Force” – is an independent panel of experts that systematically reviews the evidence and develops recommendations for screening tests. It evaluates the “net benefit” (benefits minus harms) of each test based on age, sex, and other risk factors for disease, and then makes recommendations about who should be getting which tests.

Although many organizations issue recommendations about screening tests within their purview, the recommendations of the Task force are considered the “gold standard” – meaning the best available. The Task Force grades its recommendations as follows:

A.  Strongly recommends that physicians provide the test, because it found good evidence that it improves important health outcomes and the benefits substantially outweigh harms.
B.  Recommends that physicians provide the test because it found at least fair evidence that the test improves important health outcomes and the benefits outweigh harms.
D.  Recommends against routinely providing the test to asymptomatic patients because it found at least fair evidence that it is ineffective or that harms outweigh benefits
C.  Too close to call -- no recommendation for or against providing the test because it found fair evidence that it can improve health outcomes but the balance of benefits and harms is too close to justify a recommendation
D.  Insufficient Evidence -- no recommendation for or against providing the test because the evidence about effectiveness is lacking, of poor quality, or conflicting, and the balance of benefits and harms cannot be determined. 

As you can see, Task Force recommendations are based largely on the “quality of the evidence.” It grades the quality of the evidence for a screening test on a 3-point scale, namely “good,” “fair,” “poor”:

• Good: Evidence includes consistent results from well-designed, well-conducted studies in representative populations that directly assess effects on health outcomes.
• Fair: Evidence is sufficient to determine effects on health outcomes, but the strength of the evidence is limited by the number, quality, or consistency of the individual studies, generalizability to routine practice, or indirect nature of the evidence on health outcomes.
• Poor: Evidence is insufficient to assess the effects on health outcomes because of limited number or power of studies, important flaws in their design or conduct, gaps in the chain of evidence, or lack of information on important health outcomes.

In many instances, screening is controversial not because the test in question doesn’t work, but because it is not clear whether early detection and treatment truly benefits people with the disease.

With all that background, we can better understand the recommendations of the Task Force. For the screening tests of greatest interest to our readers, the recommendations are summarized in this chart. We have organized the recommendations based on their strength “for” or “against” screening, and then alphabetically within each category. We have also included comments to help readers put the recommendations in perspective.

Dr. Alan Kronhaus is owner of Doctors Making Housecalls. The number is 919.932.5700 or visit www.doctorsmakinghousecalls.com

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