Screening Vs. Diagnosis: How Do These Two Procedures Relate to Each Other?

Doc Gumshoe on patient screening, including PSA tests and Body Mass Index

[ed. note: Michael Jorrin, who I dubbed “Doc Gumshoe” years ago, writes for us a couple times a month on medicine and health issues. He is not a physician, but explains the science and the data well, and helps provide some background understanding and perspective that often benefits both investors and folks who are attentive to their own health. He doesn’t focus on investment ideas, but follows our trading rules when investments are featured in his articles. You can see his past articles and comments here.]

What made me think about those fundamentally different procedures was Travis’s piece about the “Biggest medical breakthrough of the decade.” In case you missed that entry, this turns out to be the Trovagene (TROV) urine test that detects the specific DNA of cancer cells. From the standpoint of the patient, nothing is simpler than a urine test. From the standpoint of the technology that would identify the DNA, that screening procedure, although simple, could lead to a diagnostic process that was in fact highly complex and required the most advanced technology. Doc Gumshoe is not a stock analyst, and I would not dream of assessing the likelihood that Trovagene stock would zoom and make a bundle.

At this point, only one clinical trial seems in any way to be connected with Trovagene, and that one is an observational study looking at DNA mutations in patients already diagnosed with lung or colorectal cancer. That is probably not the cancer screening test touted as the “biggest medical breakthrough of the decade.” I pointed out in a comment on that post that identifying the cancer cell DNA would not likely point to the location of the cancer, nor the stage. To arrive at a diagnosis would likely require imaging, and perhaps biopsy or exploratory surgery. The urine test is merely a screening procedure. If it’s positive, what’s the next step?

That’s always the question with screening. When we go for a routine physical, many of the things the health-care provider/doctor carries out are screening procedures. “Screening” implies that just about every patient, or every patient in a certain group, will undergo that procedure. We get weighed and measured, and the doctor calculates our body-mass index, or BMI. That’s a screening procedure, because there’s an assumption that a BMI over a certain value predisposes us to some health problems. But it’s not a diagnosis of those health problems. Our heart rate and blood pressure are measured. We have an electrocardiogram (EKG). A blood test provides information on a great many important parameters, including lipids, blood glucose, and liver functions. Our blood-oxygen level is assayed. And those are only a few of the screening procedures we go through.

None of those procedures are diagnostic. A diagnosis presumes that the patient presents with symptoms or other indications of a disease or disorder, perhaps discovered by means of screening. The purpose of the diagnosis is to determine the cause of these indications, and – we hope! – to point the way to a treatment that cures or at least manages the un