Genetic Testing: What You Need to Know

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What happens during genetic testing?

Genetic testing is typically done only if you and your health care team feel sure that it’s the best thing for you and your family. Usually there are several steps before the actual testing is completed. (Some genetic tests are sold as home-based kits that you can buy online. The process for these tests will vary depending on the company that offers them. For more information on these types of tests, see the section “What’s the future of genetic testing?”)

Risk assessment

The first step in genetic testing is to find out how likely you are to develop a certain disease. This risk is based on the pattern of disease in your family (called a family history) and other factors. Your risk may be looked at by a doctor, nurse, or trained genetic counselor.

You will be asked about your reasons for wanting genetic testing. Your family history (as far back as possible and up to the present day) will be reviewed in depth. The patterns of disease in your family will be identified. It’s important to confirm the illnesses in your family by medical records and/or death certificates when possible. If the genetic testing is for a certain type of cancer, you may also be asked about your own medical history. This may include early detection practices, gynecologic history (for women), lifestyle factors, and exposure to things that can cause cancer (carcinogens). You may also have a physical exam that focuses on the cancer of concern in your family.

It’s often helpful to look at your family’s attitudes about cancer and the possibility of a family member being “blamed” for the cancer. Cultural beliefs, support systems, and finances may also play a role in how your family views cancer. These topics may be discussed, too.

Genetic counseling

Genetic counselors have special training and graduate degrees in their field. Some doctors and advanced practice oncology nurses with special training may also do genetic counseling.

The purpose of genetic counseling is to give you information in an unbiased or neutral way so that you or you and your family can make your own decisions about whether to get tested. Sometimes the need for testing is clear and a doctor will recommend testing and follow-up care. But even if that’s the case, you have the right to refuse testing. You may feel more comfortable making a decision after you talk with a genetic counselor. In fact, some health insurers require you to get genetic counseling before genetic testing will be covered.

The counselor will discuss how families inherit cancers and how genes are passed on to children, as well as the types of cancer seen in the family and estimates of the person’s cancer risk. The pros and cons, cost, and limits of testing are discussed too, as well as who in the family should consider being tested. More than one family member may be offered testing.

For example, if testing shows that the person has a high cancer risk, the counselor may also talk about the best ways to manage it. These may include lifestyle changes, early detection, watching for signs and symptoms of cancer, medicines to reduce cancer risk, or even preventive surgery.

Many of these issues require an expert counselor. An increased risk of cancer, especially for children, and the potential for discrimination can be frightening. The counselor will explore ways to cope, as well as your specific fears and concerns. How to discuss the test results and what they mean with other family members is another key topic.

Your doctor can probably refer you to a genetic counselor in your area. If not, you can find a list of certified genetic counselors on the websites of the National Society of Genetic Counselors or the National Cancer Institute. (See the “To learn more” section at the end of this document for more information.)

Informed consent

After risk assessment and genetic counseling, if you decide to be tested you’ll be asked to give your informed consent in writing. The process of informing you and your family about testing should cover:

  • The purpose of the genetic test
  • The reason for offering the test to you and/or other family members
  • The type and nature of the genetic condition being tested for
  • Test accuracy
  • Pros and cons of testing (including the limits of what the results might tell you)
  • Other testing options you could use
  • Treatment options that might be available depending on the test results (if this applies to you)
  • Further decisions that may need to be made once the results are back
  • The possible consent to use the results for research purposes after the test
  • Availability of counseling and support services
  • Your right to refuse testing

For more information on this process, please see our document Informed Consent.

Specimen collection and lab testing

Once you have signed the consent form, lab tests are done on cells taken from your body. Genetic tests may be done on a sample of blood, cheek cells, urine, amniotic fluid (the fluid that surrounds a fetus during pregnancy), or other body tissues.

Genetic tests for cancer usually mean you will give several tubes of blood. A thin needle is put into a vein (usually in your arm) to get the blood.

Getting test results

Once the testing is complete, the lab reports the results in writing to the doctor or genetic counselor. You will then be given the results during another counseling session. This may not happen until several weeks after the samples are taken. The accuracy of the test and the meaning of the results will be discussed with you in detail.

If the result is positive

If the results of the test are positive, you have a mutated gene (or genes) that may place you at risk. Your risk of developing the cancer will be discussed in light of the fact that you have the mutation.

Many people are concerned or anxious after learning they are at increased risk for cancer. This is normal. The results may lead to strains in family relationships as well. Concern about being treated differently may become more real.

Even after the testing is complete there’s often a great deal of uncertainty. In most cases, there’s no way to know if the disease will even develop. And even if you were to know you will get the disease, you still wouldn’t know when it might develop. Your doctor or counselor can help you sort through your options at this point, including what you might be able to do to help lower your risk.

If the result is negative

If the test result is negative, it means the gene mutation that was tested for is not present. You will probably feel relieved that the test did not show you are at increased risk.

But it’s important to understand that genetic test results can’t always guarantee you’re not at increased risk. For example, there might still be a chance that you have a mutation that you were not tested for. (Many genes can have more than one kind of mutation that can result in higher cancer risk.) And rarely, the test result may be a “false negative.” This means the test reads negative but the mutation is actually there. But even a result that’s truly negative does not mean your risk is zero – it just means you have the same average risk as most other people.

Family members with negative test results may feel guilty if other family members test positive. Your doctor or genetic counselor can help you understand what the test results mean for you and your family and how to deal with them.

If the result is inconclusive

If there’s not enough information to know whether the genetic changes are present, the test result is said to be inconclusive. The person (and family) may still be at a higher risk of developing cancer. Taking steps to lower your risk and have some control over your health can be helpful for some people, but not having a sure result can still cause anxiety and frustration. Your doctor or genetic counselor can help you understand what the results might mean for you and your family and help you cope with them.

If the result is variance of unknown or uncertain significance

This result can happen when genetic tests show that a person has an unusual form of a gene, but its meaning is unclear. It can be a normal variant, simply a different version of gene that isn’t seen often enough to be sure, or there may be some other explanation. For some, a variance of unknown or uncertain significance (VUS) result can cause anxiety, frustration, and even anger because this result gives no information to guide future decisions. Your doctor or genetic counselor can help you understand what the results might mean for you and your family and help you cope with them.

Last Medical Review: 10/18/2013
Last Revised: 03/11/2015