Ten years ago, I noticed a golf ball–sized lump on my torso. My family doctor sent me to a surgeon, who removed the lump and sent it to a lab for testing.

A few weeks later, I got the news from my doctor: “You have a very rare type of lymphoma.” I froze with fear. The second blow came when an oncologist told me that if I didn’t start chemotherapy right away, I’d be dead within months.

But I didn’t feel sick, and my intuition told me that something was off with the diagnosis. So I sought a second opinion from another oncologist, who reviewed my case and had the biopsy analyzed again. As it turned out, I didn’t have cancer. The lump was simply an inflamed bundle of fat cells. I didn’t need chemo, and 10 years later I’m fine.

So how do you make sure that you or a loved one never experiences a misdiagnosis nightmare? It happens a lot. Twelve million Americans are misdiagnosed each year.

For the past decade, I have dedicated my life to helping people become smarter patients and, in the process, avoid misdiagnoses. Some of what I’ve learned may sound a little unconventional, but I know from my experience and that of other patients that the steps below work. How to avoid a misdiagnosis…

SECRET #1: Track your symptoms. You probably know to write down your questions before seeing a doctor, but I suggest that you first spend at least a little time tracking your symptoms. Medical symptoms can be vague, inconsistent and wax and wane unexpectedly, so patients often don’t give their doctors enough facts to ensure a correct ­diagnosis. Without such details, it’s easy for physicians to jump on the most obvious—though sometimes incorrect—diagnosis.

What to do: If you’re not dealing with an emergency, keep a diary of your symptoms before you see your doctor. Include a clear description of all your symptoms and when they started. Also, be sure to include any triggers—anything that makes the symptoms worse…or better.

Of course, don’t let your symptom tracking become an excuse to delay going to the doctor. Even if your appointment is the next day or so, you can use that time to organize your notes on what you’ve observed so far. And once you’ve tracked your symptoms, you’ll be better prepared to write down your questions for the doctor.

SECRET #2: Make a list of possible diagnoses. If you’ve got an unexplained symptom, most doctors tell you to avoid the Internet. You will just confuse yourself, they reason. I disagree. If you’ve got a weird symptom, you want to know what may be causing it so that you can ask the doctor intelligent questions.

When doing research online, just make sure you don’t jump to conclusions. And skip websites that are sponsored by pharmaceutical companies or businesses trying to sell you something. Also, disregard comments and forums populated by non-health professionals. Up-to-date and reliable health information is available at such sites as MedlinePlus.govHealthFinder.gov…and UpToDate.com (it’s used by many doctors around the world—click on “Patients and Caregivers”).

In my own situation, using the Internet helped me to realize that cancer wasn’t the only possible diagnosis, and it compelled me to ask many more questions.

Important: Don’t try to diagnose yourself…and don’t talk yourself out of going to the doctor.

SECRET #3: Ask this crucial question. Your doctor has just given you a diagnosis. Now what? Rather than launching into a discussion about the best treatments for the diagnosis you’ve just received—as most often occurs—I suggest that you stop and ask the doctor, “What else could it be?”

Specifically, ask the doctor for the “differential diagnosis”—that is, the conditions he/she ruled out. Then ask how he ruled them out. Listen carefully—if there are any gaps in the case he makes for your diagnosis, they are likely to come up at this time. After this explanation, ask about anything you don’t understand. Be concise and stay focused. If you start to ramble, your doctor won’t stay engaged.

SECRET #4: Don’t be afraid of your doctor. There are ways to get what you need and ask your questions without offending anyone.

What you need to know: A good, ethical doctor won’t be upset by your desire for additional medical opinions. Getting more than one opinion is crucial, especially if your doctor has recommended any invasive type of treatment such as chemotherapy, surgery or a long-term drug prescription.

Ask for your own medical rec­ords, and take them to additional opinion appointments. Your goal is to find at least two doctors who give you the same diagnosis, maximizing your odds of getting a correct one. Let new doctors draw their own conclusions about your diagnosis rather than sharing previous opinions they can simply agree with.

If your online research doesn’t jibe with what your doctor has told you, don’t be confrontational. Instead, ask questions like, “I recently read about this (diagnosis or treatment). Can you tell me why you ruled that out?” This acknowledges your doctor’s extensive education and experience but puts him on notice that you’ve done your homework and need to know more.

Getting extra help…

If you or a loved one is dealing with a serious illness and seeing multiple doctors, hiring an independent, professional patient advocate can help you decipher a diagnosis, choose the right treatment, coordinate care and obtain the support and information you need. These advocates work directly for patients—not hospitals or insurers. Hourly rates range from $75 to $300, based on location and the advocate’s expertise. To find an advocate near you: Go to AdvoConnection.com.