Screening 101

Words are my friends, so it bothers me a great deal to see them abused. One word that gets beaten up a lot these days is "screening".

As we all (should) remember, "screening" means something very specific: as I describe it to patients, it means looking for a disease or condition when you don't expect to find it. If there are symptoms you're trying to explain or history that suggests the presence of a certain condition, you are not "screening" for it.

Screening tests are very carefully evaluated in terms of prevalence of the disease or condition, the ease and availability of the test, the sensitivity and specificity of the test, the costs of the testing, and perhaps most importantly, how much of a difference in the natural history of the disease can be made by earlier detection. These criteria are what have been used to determine that colonoscopy is a good idea for colon cancer and routine chest x-rays are a bad idea for lung cancer, counterintuitive as it may sound.

My problem is the confusion of screening with diagnosis. Mammography is a great screening test for breast cancer, but when you're evaluating a palpable mass you are no longer doing a screening test. You are evaluating the mass you can feel. (Actually, what you're really doing is making sure there isn't another, non-palpable abnormality in the contralateral breast, since you're obligated to further evaluate the palpable abnormality with ultrasound, biopsy or both; it still isn't "screening", though. But I digress...)

Another problem with screening is that we do a great number of things as de facto screening tests that haven't been subjected to the rigorous analyses required to determine their value. Treadmill stress tests -- especially with nuclear imaging -- on asymptomatic patients, cardiac risk factors notwithstanding, are probably the one most demanded by the non-medical public, and/or pushed on them by doctors with equipment in their offices as revenue generators. Echocardiograms on anyone with a pulse fall into the same category. Is anyone aware of a cardiologist who has not ordered an echo on any given patient? I'm not.

The real problem with this is that valuable and proven opportunities for meaningful screening fall by the wayside as we try to educate patients about why whole body CT scanning for calcified arteries doesn't mean squat, and why "Virtual Colonoscopy" -- nothing more than fancy computer processing -- isn't ready for prime time.

It all just goes to prove the Fifth Law of the Dinosaur: A patient's acceptance of any screening test is inversely proportional to its necessity for that particular patient.