5 Blood Tests That Are Worth the Prick

The Blood Test for the Vitamin Most of Us Lack

What it does: A 25-hydroxy vitamin D blood test is used to determine how much vitamin D is in your body.

Why this matters: As well as helping your bones absorb calcium and keeping your muscles strong, vitamin D provides crucial support for your immune system and may lower your risk of developing cancer and depression.

Who should get it: Anyone who worries they might not be getting the right amount of D should consider this test, and that covers an awful lot of us: 53 percent of women, 41 percent of men, and 61 percent of kids have insufficient levels.

What else you should know: The daily dietary allowance recommended by the Institute of Medicine is around 600 IU for most adults. Fryhofer likes for her patients take a vitamin D1000 IU supplement. She usually checks on them once a year to make sure their levels are balanced (the test isn't always covered by insurance, but it's not expensive, she says). Other doctors don't do this as part of a routine visit, so you'll need to ask.

The Blood Test That Can Save Your Liver (And Your Life)

What it does: The Hepatitis C test detects a liver disease that results from infection with the Hepatitis C virus.

Why this matters: While the Centers for Disease Control and Prevention (CDC) data shows that more than 3 million Americans are living with the virus, 75 percent don't know that they're infected. Over time, untreated Hepatitis C can lead to liver damage, cirrhosis and cancer.

Who should get it: The CDC guidelines are still new, so you may need to prompt your doc, says Pregler. Hepatitis C can affect anyone, but those born between 1945 and 1965 have the highest rates of infection, and younger people may want to talk to their doctor about risk factors to see if the test makes sense for them, too, says Pregler.

What else you should know: Treatment for Hepatitis C used to involve a grueling regimen of drugs with unpleasant and sometimes dangerous side effects. But late last year, the FDA approved two drugs that make treatment not only easier but also faster and more effective.