Last week, Dallas Mavericks owner Mark Cuban caused quite a stir on Twitter by suggesting that people, if they could afford it, get quarterly bloodwork to establish a baseline of their own health. A big failing of medicine, he wrote, is that "we wait till we are sick to have our blood tested and compare the results to 'comparable demographics.' "

https://twitter.com/mcuban/status/583366647987093504

While that idea may seem logical, medical researchers have long cautioned that more testing is not a recipe for better health. I and others, including many doctors, countered Cuban's views, saying they could produce dangerous outcomes for patients. (You can find my summary here and here.)

Here's why: More testing leads to more false positives and incidental findings (abnormalities that don't pose a risk to your actual health). That leads to a higher probability of treatment. And treatment carries side effects.

The Society of General Internal Medicine explicitly discourages routine general health checks for adults who have no symptoms, saying they have not been shown to reduce illness, death or hospitalization, but do create "a potential for harm from unnecessary testing."

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It was an interesting discussion, and Cuban did not back down. Indeed, some doctors said that Cuban's vision may be the way of the future, particularly as medical testing improves and patients grow more accustomed to managing their own health data. "Many companies are pushing big data in healthcare," writes Dr. Michael H. Tomasson, a hematologist at Washington University in St. Louis, on his blog. "I see no reason why Cuban can't push too in his own way."

Mark Cuban, owner of the Dallas Mavericks, stirred debate last week with his suggestion that quarterly blood testing could help healthy people stay that way. (Doug Pensinger/Getty Images)

I asked Cuban to continue the discussion in a podcast and an interview. He declined, saying my position on the issue rendered me partial. But he explains more of his thinking in comments he posted on The Health Care Blog.

To get some additional perspective, I turned to Dr. H. Gilbert Welch, a professor of medicine at the Geisel School of Medicine at Dartmouth College. Welch is a leader in articulating the case against testing too much. His take on the question at hand was never in doubt, but the reasoning behind it is important.

This interview has been edited for length and clarity.

Is quarterly bloodwork for healthy people a good thing?

No. It's not. This is potentially a recipe for making all of us sick.

I guess the first thing to say is that we all harbor abnormalities, and increasingly our technologies are able to detect them — be they biochemical, be they structural. We can see things down to millimeters in size; we can measure things down to parts per billion; and we can sequence the whole genome. That's 3 billion data points.

So there's no shortage of biometric data that people could be collecting on themselves regularly, and by the way, there's a huge financial interest in having people do that. The market of the well is a huge, huge market.

The problem is you'll always be catching things out of what we would say is normal. This is anticipatory medicine at its worst, where you're really focused on what could be going wrong in the future and you're trying to pick up [a] signal.

The problem is there's so much noise — because the human body is a living organism. Variation is the very essence of life. People will start reacting to this data. I also think it's really important to label it what it is: data. To me it only becomes information to the extent that it accurately predicts something will happen in the future, and it only becomes useful knowledge — a higher level piece of information — if we can do something about it.

Cuban argues that any misdiagnoses and unnecessary treatment rests with the doctors, and not with patients owning their data. Do you agree?

I think there's a misunderstanding that diagnosis is some super clear black-white kind of distinction, when in fact there are 1,000 shades of gray in between. The time you get into that gray is when you're dealing with people who feel fine and have some detectable abnormality. That's how we get into it in cancer screening. We're looking for very early signs of disease. There's going to be great pressure to react to those abnormalities.

It's not fair to say the pathologists have misdiagnosed. Undoubtedly there is some misdiagnosis, but their standard for what constitutes cancer is the appearance of individual cells, and how they relate to one another — the architecture of the cells.

That was a perfectly good standard when you were sending them cancers that you could feel, things the size of golf balls. But when you start sending them microscopic collections of cells, expecting them to make some prediction about the dynamics of that process and how that will interact with the host — that's you – it's understandably going to be fraught with uncertainly. It's all going to be probabilistic.

Some people say that medicine needs to move away from paternalism and more toward individual ownership of health. Patients want access to their own data, how and when they want it.

I'm a great believer in having patients share in decisions. At the same time, since I've actually cared for patients, I know that many times they're sick. They actually want to know what your advice is. It's too easy for doctors to come back and say, 'What do you want to do?' Obviously we have to find a balance between something that's totally on the patient to try to decide ... and the doctor simply asserting what the patient should do.

I think most patients want to be somewhere in between. They want to participate in the decision, and when there really are close calls, they want to participate in the close calls. We should recognize that some patients will want to do that more than others, and some patients will be more capable of doing that than others.

We should also be clear that there's a lot of bad information out there.

Cuban makes a distinction between making a diagnosis, and collecting a series of data points to "benchmark" yourself.

The more tests you do, and this is only the statistical process, the more likely one of them will be falsely abnormal. And the more times you do it, the more chance that something will be falsely abnormal.

There will be great pressure to take actions and that's how people will get hurt. It's going to distract them from the more positive things that they can do now.

It gets down to what health is. What I'm worried about is allowing health to be defined as some set of biometric measurements. ... Health is about more than a bunch of physical measurements. It's about a state of mind and we have to be careful not to undermine that state of mind. Ironically, part of health is not being too focused on it. ... Much better for people to develop good relationships, have good friends, be outside, eat well — find things that produce meaning in their lives.

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This post comes to us via NPR's partnership with ProPublica.

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Tracking Your Own Health Data Too Closely Can Make You Sick