The US Preventative Services Task Force was created in 1998 to tell you and me what medical tests we should undergo to screen for cancer, diabetes, and other diseases. The panel answers questions such as — should women over 65 who have otherwise been healthy be screened with pap smears for cervical cancer? Each recommendation receives a grade based on the level of certainty that the test is worthwhile. In the above case, pap smears for women over 65 scores a D, i.e. they should not be done.
Before the panel started releasing its reports, the maxim was to offer screening tests as widely as possible. What harm could they do, right? Problem is that not only do certain tests do some harm (e.g., radiation from X-rays), but screening tests run on patients with a low likelihood of having the disease give poor predictive values. This flows into what I consider the most important concept for a patient to understand here: Pre-test probability, the chance that you have the disease for which you are being screened.
The task force recommends that men of 35 and above be screened for elevated cholesterol levels. Why don’t they suggest 15-year-old boys be tested? The reason is that the likelihood or pre-test probability for teenagers to have elevated cholesterol is extremely low. Fats in your blood increase with age. In the US, by 40 the lifetime risk of having a heart attack is 49 percent for men and 32 percent for women. And since one-third of all heart attacks are linked to patients having elevated total cholesterol levels (greater than 200 mg/dl), screening for cholesterol should start by 35.
Preventable chronic diseases are now officially the biggest killers. Listed below are scoring definitions and some of the task force’s key screening guidelines.
Grade A: Net benefit is substantial, recommend service.
Grade B: Net benefit is moderate to substantial, recommend service.
Grade C: Net benefit is small, recommend against routinely providing service.
Grade D: No net benefit, recommend against service.
I Statement: Evidence is insufficient to assess benefits and harms.
Breast Cancer Mammography should be performed every two years in women between ages 50 and 74. Grade: B.
Colon Cancer All adults starting at 50 years until 75 should undergo screening for colon cancer by a simple examination of blood in the stool, or a colonoscopy. Grade: A.
Prostate Cancer This is controversial, but if you have faith in our cancer treatments as I do, the recommendation would be to screen men between 50- 74 years with a prostate specific antigen (PSA) test every four years. I Statement.
Heart Disease The task force did not find enough evidence to recommend adults to be screened with a treadmill test, electrocardiogram, or computerised tomography (CT) of coronary arteries though each of these are increasingly popular components of executive health checks. Grade: D.
Osteoporosis Women over and under 65 who have other risk factors for fractures should have a bone mineral density test at most every two years. Women lose the bone protective effect of estrogen after menopause and have a far higher risk of osteoporosis than men. Grade: B.
Diabetes Adults with blood pressure over 135/80 mmHg should be screened with a fasting blood sugar test. Grade: B.
So, should we all have pap smears? Well, my pre-test probability of having cervical cancer is zero. But sexually active women should have one every three years until 65. Grade: A.
Dr. Kumar, and our health team, can be contacted at email@example.com
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(This story appears in the 20 May, 2011 issue of Forbes India. To visit our Archives, click here.)