Ken Berger, a San Diego geography professor, says living with the unknown was torture. "No physician could figure out what was wrong," he says. (Edna P. Berger / June 22, 2011)

A few years ago, Ken Berger noticed a small mass in one of his testicles, and scheduled a next-day appointment to get it examined. An ultrasound revealed a lump, but other tests came back negative for testicular cancer — except for one.

To his frustration, a commonly used cancer blood screening test came back with a reading outside normal range — though not enough to confirm a diagnosis.

So he visited multiple specialists, and the doctors ran more tests. The one test continued to return fluctuating results. His levels never got high enough to confirm a diagnosis — yet remained too high to completely rule out cancer. This went on for a year and a half.

"No physician could figure out what was wrong," says the 63-year-old geography professor from San Diego. Living with the unknown, he says, was torture.

"Do I have cancer, yes or no? Once the decision is made — good or bad — at least you can say OK, this is the result and now you can start planning and get on with your life. It's better to know," he says.

Missed or incorrect diagnoses plague millions of Americans like Berger each year. A recent study published in the British Journal of Medicine found that diagnostic errors affect about 12 million people in the U.S. each year.

These incorrect diagnoses — or none at all — often take a financial and emotional toll on patients as they struggle to navigate a complicated medical system to figure out what's wrong.

Here, experts offer recommendations for patients eager to unearth the source of what ails them:

Work with a primary care physician. It's important to work with a primary care physician so that all doctor visits, tests and other treatment information is being monitored by one physician overseeing your entire case.

"If you go to a pulmonologist, they'll test your lungs because that's what they know. Going to a specialist is a bad idea until you know what's wrong. That's why primary care physicians are so important, because they look at the whole person," says Dr. Leana Wen, an emergency physician at George Washington University and co-author of "When Doctors Don't Listen: How to Avoid Misdiagnoses and Unnecessary Tests."

Take an active role. "Communicate with your doctor that you want to be an active participant in your care," she advises. Just stating that can make a big difference in how your doctor treats you, she says.

Show up to your appointment prepared to discuss your condition and the medications you're taking. This gives the doctor more time to listen to you.

"On average, physicians spend eight minutes to see patients. There isn't time to go over a complex history," says Dr. Bettina Experton, chief executive of Humetrix, a healthcare information technology company based in Del Mar.

For that reason, it's a good idea to jot down notes in advance of the visit to include a brief history of your symptoms, the medications you're taking and any tests or scans you've undergone.

Also, consider keeping your own electronic personal health record, which can be a more efficient way to receive and transmit the summary of your medical care to any doctor or health system you visit.

"I can't overstate the importance of the patient history in coming to a diagnosis," says Dr. David Harrison, medical director for Best Doctors Inc., a service based in Boston offering second opinions on medical cases.

Get a second opinion. It's always a good idea to get a second opinion, especially when there is a complex set of symptoms without a clear diagnosis, Harrison says.

"Even if people go through the process and don't find new answers but confirm what their first doctor is saying, it's important to know you've left no stone unturned," he says.

Most insurers cover the cost of a second opinion. And, in California, HMOs are required to pay for a second physician consultation.

Harrison suggests that people stay within the same medical system, if possible, especially if it has a shared electronic medical record. That can reduce the chance of your medical information becoming fragmented.