Diagnostic testing is the situation where an individual is suspected of having a particular condition and a specific gene/s is/are tested to look for disease causing mutations. This can confirm the clinical diagnosis for the patient.

Genetic testing holds great potential for the future of medical care. It offers many benefits, including providing important information that can be used when making decisions about having a family and taking care of one’s own health. However, there are also limitations. For this reason, it is important to understand the nature of genetic testing and the information that it can and can’t provide. For example:

  • Predictive tests can determine if a person has a disease causing mutation or variant which may, at a later date, cause a particular genetic condition. However, we usually cannot predict the timing of disease onset or the severity of the condition. Such results are not definitive and may leave a person wondering what to do with those results. Predictive testing should be done with advice from a clinical geneticist or a genetic counsellor familiar with the disease.

  • A particular genetic test will only provide information about the specific gene/disease being tested for. It does not provide information about other genetic diseases not being specifically looked for by that test.

  • While the test may detect a particular problem gene, it cannot predict how severely the person carrying that gene will be affected. For example, with cystic fibrosis, symptoms may range from mild bronchial abnormalities to severe lung, pancreatic, and intestinal problems.

  • Many genetic tests cannot detect all of the variations that can cause a particular disease. For instance, with genetic testing for cystic fibrosis, most genetic testing panels only look for the more common variants, not all of those that are associated with this disease. So, not finding a gene alteration may not exclude the condition. The doctor may still make the diagnosis if the clinical findings strongly indicate that the person does have the disease.

  • Many diseases are the result of an interaction between a person’s genes and their environment. The way in which these interactions cause disease is not clearly understood. Examples of these diseases include coronary heart disease, type 2 diabetes, obesity and Alzheimer's disease.

  • If a person is found to have a genetic variant that has implications for health then this may be relevant for other family members such as brothers, sisters, children and other relatives. These relatives may or may not want to know about the implications for themselves and handling the information obtained from genetic testing can be difficult and complex.

  • Legal issues, such as patient privacy, use of genetic testing to determine insurance coverage, and the use of archived patient samples are some of the broader social issues to be considered.

Because of these limitations, genetic test results can be a mixed blessing. An absolutely essential component of clinical genetics testing is giving your informed consent to do the tests and knowing what you want to do with the results of these tests. Know your legal rights as well. Make certain that your privacy is respected. Educate yourself about genetic tests, and talk to your medical provider if you think you should have genetic testing performed. This is especially important as more genetic testing becomes available directly to consumers.