Imagine being rushed to the hospital with appendicitis, but your medical records show that your appendix has already been removed. The confusion could delay proper treatment.
What if your blood type is different from what's listed in your medical file? Or maybe you have severe drug allergies, but the records have been changed and now say you don't have any.
This is what can happen to victims of medical identity theft, a rapidly growing problem that few people know about it.
Medical ID theft takes place when someone uses your name and personal identifying information to receive medical services, devices or prescription drugs.
"It's an insidious crime, and the consequences can be deadly," said Robin Slade with the Medical Identity Fraud Alliance (MIFA). "This fraud causes your medical records to get contaminated by the perpetrator's medical information, so it could literally kill you."
And this crime is on the rise—up 20 percent within the last year, according to a national survey from the Ponemon Institute, which specializes in privacy issues.
"We don't think this is an anomaly," said Dr. Larry Ponemon, the institute's chairman. "We think this crime is becoming more popular with criminals because a medical record is actually more valuable than other forms of personally identifiable information, like a credit or debit card record."
(Read more: Credit card confusion: How do I earn rewards?)
This study, which Ponemon conducted for MIFA, estimates that nearly 2 million Americans have been victims of this crime and will spend over $12 billion out of pocket this year alone to deal with the consequences of their compromised medical or insurance files.
With most forms of identity theft, you realize you've been the victim fairly quickly. It doesn't take long to discover that your credit card number was used by a thief on a shopping spree.
But medical identity theft can be perpetrated without your knowledge.
"It may be years or decades later that you find out that your medical record has changed, putting you at great peril," Poneman told me.
Such a discovery can come as quite a shock.