Just Because You Can Screen For Serious Diseases, Should You?

Just Because You Can Screen For Serious Diseases, Should You?


Leonard Zwelling


In The New York Times Science section on March 5, Paula Span reports from the front lines of Alzheimer’s diagnosis and treatment that a blood test may be able to identify someone likely to develop Alzheimer’s Disease prior to the patient displaying any symptoms.

Then what?

This is not like breast cancer, prostate cancer, high cholesterol, or glaucoma. There’s not a whole lot a doctor can do about someone who’s serum markers indicate the likelihood of Alzheimer’s. Even if you believe the wisdom of the FDA’s approval of a few amyloid-targeted drugs (I do not), they are pricey and have never been shown to suppress the development of clinically-significant dementia in the asymptomatic population.

I think the criteria for screening ought to be whether or not the identification of a susceptibility to a disease leads to a meaningful intervention to prevent or delay the development of the disease. Can the natural history be altered?

Mammograms, colonoscopy, PSA, Pap smears, and a host of blood screening done during routine annual physical exams may do just that—identify unsuspected disease and open a window for intervention to alter the natural history of the disease for the patient’s benefit. This is clearly not the case with Alzheimer’s quite yet.

This also causes one to examine a new trend for asking doctors to order full body scans (CTs, MRIs) looking for unsuspected cancers. The Galleri Grail blood test that detects methylated circulating cancer DNA as a screen for latent malignancy is right on the edge of being useful. It appears to be effective. My own physician has used it to diagnose an unsuspected stage 2 pancreatic cancer in one of his patients, but the cost is significant with this blood test (about $800), so like the full body scanning, this may be for the rich only.

When to do what in the way of screening is usually decided by the US Preventive Services Task Force. This group weighs the evidence for or against screening tests and makes recommendations that influence practice like the CT screening of former smokers for lung cancer.

Yet, in the end, the real determinative factors are a doctor’s beliefs, a patient’s

desires, and the finances.

For myself, I make my own choices.

I continue to screen myself with PSA test although I may be beyond the age where the USPSTF thinks I need it. I still get annual blood work and a physical exam as well as an EKG, eye tests, hearing tests (I wear hearing aids), and office-based cognitive testing. I have elected to do this with a concierge doctor as I felt when I did not have someone in this position, I was managing my own care in a way that was probably detrimental to my health.

Screening is tricky. When to do what and in what population is always up for grabs, although it is studied carefully.

I think I will forego any measurement of my blood amyloid given there isn’t much to be done if it is a positive test and a positive test is not definitively predictive of my clinical course. And that ought to be the criterion.

If the screening leads to a meaningful intervention, I’m for it. If not, I’ll pass. When it’s in between, (e.g., PSA in older men), I’ll have made my decisions on what to do if the PSA rises with my urologist. It’s best to have a plan before doing the screening. It tends to deplete emotion from the equation.

2 thoughts on “Just Because You Can Screen For Serious Diseases, Should You?”

  1. Excellent discussion! Thank you.
    Let’s add screening for an abdominal aortic aneurysm with ultrasound at age 65 in ALL males who have smoked more than 100 cigarettes in their lifetime. At least ten percent will have a AAA. A British study showed that this recommendation decreased significantly death from rupture. (Medicare now covers this screening.)
    Also, atrial fibrillation is so common and so related to embolism and stroke that regular monitoring of heart rhythm, especially by a smart phone, is also a reasonable expenditure.

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