Genetic tests are conducted for the purposes of establishing or clarifying a clinical diagnosis. An example is the use of a molecular genetic test to determine if a child with developmental delay has the diagnosis of Fragile X syndrome, the most common inherited form of mental retardation in males (Bailey, Skinner, and Sparkman 2003). This condition is caused by a mutation on the X chromosome that can be identified through molecular genetic testing. When a test is conducted for the purpose of diagnosis, family members may not complete the full informed consent process. One component of that process is to review the potential outcomes of a test. In this instance, because the test is attempting to establish the diagnosis of a condition that can be inherited within families, nurses share responsibilities with other healthcare providers to ensure that persons agreeing to the test understand its purpose and the potential implications of the result for other family members.

Genetic tests are also conducted to determine if persons who are not ill could be carriers of inherited conditions. A person consenting to a carrier test may wish to know if he or she has an increased likelihood to have a child with an inherited condition. Some conditions have an autosomal recessive pattern of inheritance, meaning that a mutation must be present in each of the two copies of the gene in order for the condition to be present. Certain inherited diseases are only manifested if the person has a mutation in each gene for an autosomal recessive disorder, or, in males, if the mutation is on the X chromosome. Carrier testing can determine if persons have only one copy of the mutation. An example of an autosomal recessive condition is cystic fibrosis (CF). In this case it is important for the individual, or couple, to understand that a carrier does not have the disease, but when they are each carriers, their children could have CF.

Genetic testing is possible for some conditions where the causative mutation is known, such as Huntington disease (HD), to determine if the person has a high likelihood of developing the condition in the future. This type of testing is referred to as presymptomatic testing (Secretary’s Advisory Committee on Genetic Testing 2000). When the purpose is to determine if a person has inherited a genetic susceptibility that increases the likelihood they will develop a disease in the future, this is referred to as predictive or susceptibility testing. When a person has a relative with a mutation in the BRCA1 or BRCA2 gene, which are associated with an increased chance to develop breast and ovarian cancer, the test could provide information about their future likelihood to develop these diseases. These testing terms may not be used consistently by healthcare providers. Thus, it is essential that people considering genetic testing to provide information about future chances of developing a disease have a clear understanding of what type of information the test can provide for them.

One aspect of answering this question is the clinical validity of a test. This refers both to the sensitivity, i.e., the proportion of people with the disease who have a positive test, and the penetrance of the gene mutation identified. Penetrance is the proportion of people who have the mutation who will also have signs and symptoms of the disease (Burke 2004). Individuals and families may need help in understanding what kind of information the test will provide. In one survey of parents of children who had a genetic test to diagnose Fragile X syndrome, the majority of parents found the test helpful because it provided a reason for their child’s problems (Bailey et al. 2003).

In other circumstances, the result of a genetic test can provide information that can be useful for making clinical decisions about a person’s health promotion or disease management. It is important to note that results from a genetic test are only one factor in clinical decisions. Usefulness of results in predicting future disease or selecting management options will vary for each test and clinical situation. One
example of use of a genetic test to guide screening decisions is familial cancer genetic testing. For those who are at risk for certain inherited forms of cancer, such as hereditary nonpolyposis colorectal carcinoma (HNPCC), persons who had a positive genetic test were found to be more likely to have colonoscopy screening, than those whose test was negative. In this situation, the gene test results were used to help determine which persons should continue this screening. It was also reported in this study that some persons who had a negative gene test continued to have colonoscopy screenings. Factors other than the actual test result also influence how people use genetic testing information. This is consistent with a holistic approach to patient care, when nurses consider the entire range of factors, including prior beliefs, advice from other family members or healthcare providers, extent of understanding of test results, and other sociocultural factors that contribute to how each person uses genetic test information.