(CNN) -

When you're a patient, you trust you're in good hands, but even the best doctor or nurse can make a mistake on you or someone you love.

"Mistakes are happening every day in every hospital in the country that we're just not catching," says Dr. Albert Wu, an internist at Johns Hopkins Hospital.

Medical errors kill more than a quarter million people every year in the United States and injure millions. Add them all up and "you have probably the third leading cause of death" in the country, says Dr. Peter Pronovost, an anesthesiologist and critical care physician at Johns Hopkins Hospital.

The harm is often avoidable, and there are strategies you can use to help doctors and nurses get things right.

Here's a list of 10 shocking medical mistakes and ways to not become a victim:

1. Mistake: Treating the wrong patient

• Cause: Hospital staff fails to verify a patient's identity.

• Consequences: Patients with similar names are confused.

• Prevention: Before every procedure in the hospital, make sure the staff checks your entire name, date of birth and barcode on your wrist band.

• Example case: Kerry Higuera

2. Mistake: Surgical souvenirs

• Cause: Surgical staff miscounts (or fails to count) equipment used inside a patient during an operation.

• Consequences: Tools get left inside the body.

• Prevention: If you have unexpected pain, fever or swelling after surgery, ask if you might have a surgical instrument inside you.

• Example case: Nelson Bailey

3. Mistake: Lost patients

• Cause: Patients with dementia are sometimes prone to wandering.

• Consequences: Patients may become trapped while wandering and die from hypothermia or dehydration.

• Prevention: If your loved one sometimes wanders, consider a GPS tracking bracelet.

• Example case: Mary Cole

4. Mistake: Fake doctors

• Cause: Con artists pretend to be doctors.

• Consequences: Medical treatments backfire. Instead of getting better, patients get sicker.

• Prevention: Confirm online that your physician is licensed.

• Example case: Sarafina Gerling