What if you had an expiration date stamped somewhere on your body -- a little message that says exactly how much longer you might live?

Would you even want to look at it? Would you let your family see it?

Researchers say they've found just such a mark, hidden in your bloodstream -- and they'll read yours... for a price.

It's a $700 test that measures telomeres, little caps that sit on the ends of the chromosomes inside your white blood cells.

You can find a pretty good image of them here.

Every time your cells divide, the telomeres get just a little bit shorter. Since cell division is a hallmark of aging, researchers believe the length of the telomere is a better measure of your true age than birthdays.

And if your telomeres are getting short, your time may be as well.

Of course, the test can only measure telomeres -- it can't measure dumb luck, tragic endings or pure stupidity. It can't predict whether you'll drop dead after winning a hot dog eating contest, perish in a tragic bungee jumping accident or get gored while running with the bulls.

But the test may be able to offer a glimpse into the effects of your lifestyle, genes or both -- and maybe even tell you about your disease risk, since short telomeres have also been linked to dementia, cancer, heart disease and more.

In a way, maybe the test can serve as a warning for some people: make some changes, or start planning your funeral.

On the other hand, it could also cause some people to party like there's literally no tomorrow.

In reality, all the expensive test really offers is a vague and incomplete prediction -- but if you still want to take it, consider some of the other issues here... ones that go far beyond pure physical health.

Once you get the test, for example, would you be required to reveal the results to your health or life insurance companies? Your employer? On the flip side, could employers or insurance companies require you to take the test even if you don't want to?

Already, there are employers who won't hire smokers, doctors who won't treat the obese and insurers who won't give coverage to people based on certain conditions -- and the telomere test could trump all that, the granddaddy of preexisting conditions.

Personally, I find all this too frightening to contemplate -- and have no plans to get my telomeres measured anytime soon.

If you want your own test, feel free -- but don't pay $700. U.S. companies plan to offer their own version of the service soon, and you can expect it to be as low as $200.

Just remember: A little bit of knowledge can be a dangerous thing.