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A few years ago, a 21-year-old college student came to the office of Orly Avitzur, Consumer Reports’ medical director, because of intermittent pain in his right ankle. He’d had a ski accident 10 months earlier, but the discomfort lingered, and after a Lyme disease test came back negative, his primary care doctor referred him to Avitzur to investigate the possibility of nerve damage. He had also been experiencing increasingly frequent pain and numbness in his hands for several years — and the cause was unknown.

Avitzur found no nerve damage. It was not until she asked about family health problems that she determined the possible cause of his concerns. Her patient’s mother and maternal grandmother had rheumatoid arthritis (RA), an autoimmune disorder that tends to attack the joints. Having a parent, sibling or child with RA is one of the strongest risk factors for the disorder.

The patient’s subsequent RA test came back positive, which also put him at higher risk for other autoimmune diseases as well as heart attack and stroke. So knowing a bit about the patient’s family’s health history allowed his doctor to glean a great deal of information about his current health and future risks.

To get a better picture of your own risks, put together a family history, a record of health data about several generations of relatives. A history will help you gain insight into your likelihood of developing specific conditions. It can also provide your doctors with clues they may need to reach a diagnosis.

There is no better time to gather that information than at family get-togethers. So as the holiday season approaches, start the conversation.

Choose your tool

You can simply write down your family’s information, but some digital tools make it much easier to build, update and share:

•The National Society of Genetic Counselors’ page (www.nsgc.org/p/cm/ld/fid=143) shows you how to draw a family tree.

•The March of Dimes’ form (www.marchofdimes.org/materials/family-health-history-form.pdf) considers lifestyle as well as family history.

•The Office of the Surgeon General’s My Family Health Portrait (familyhistory.hhs.gov) allows you to enter, print and update your family health history.

Get the right information

Make a list of relatives to talk with. Include parents, siblings, children, aunts and uncles, cousins, nieces and nephews, and grandparents. Ask them about current and past medical and mental health conditions, and their ages at diagnosis.

Pay special attention to conditions that developed much earlier than typical or affected multiple family members. Include pregnancy complications such as miscarriage and stillbirth, and birth defects.

Ask about deceased family members’ cause of death, other health problems and age at death. Ethnicity is important, because some diseases are more common in certain groups. Sickle cell anemia, for example, is more likely to occur in those of African, African American and Mediterranean heritage.

Talk with your doctor

Share the history with relatives and your primary care doctor, who may use the information to assess your risk of certain conditions and recommend lifestyle changes. If you have a strong family history of heart disease, for example, he may suggest a healthful diet and exercise program or encourage you to stop smoking.

Doctors may also use the history to identify other family members’ risks, choose diagnostic and genetic tests, put together a treatment plan or change intervals for screening tests. The U.S. Preventive Services Task Force, for instance, notes that women with a parent, sibling or child with breast cancer may benefit more than average-risk women from starting screenings between 40 and 49, rather than at age 50.

Without some background on your family’s health, your doctor really is at a disadvantage. In fact, Avitzur says, she was startled to learn several years ago that her brother and his son had an autoimmune disease called ankylosing spondylitis. Each went undiagnosed for years by physicians who had not tied together their individual complaints of joint pain. A family history could have meant an earlier diagnosis.

Copyright 2015. Consumers Union of United States Inc.

For further guidance, go to www.ConsumerReports.org/Health, where more detailed information, including CR’s ratings of prescription drugs, treatments, hospitals and healthy-living products, is available to subscribers.