Genetic Testing is also referred to as DNA testing (singular - a DNA test). If a doctor is ordering a DNA test, it is typically done to establish or confirm if a health condition is due to an alteration in the DNA of a patient. If a person is doing what is known as a Direct-To-Consumer (DTC) test, then most of the time it is done to get a good picture (profile) of someone’s overall health condition and if lifestyle changes should be made. A good number of people consider ancestry analysis using DNA as a genetic test as well. In our discussions here, we will not consider ancestry analysis as genetic tests but more as an application of genome analysis that is of interest to the public.
Genetic tests can also help determine if a person has a chance of developing a genetically influenced disease (some cancers like breast cancer can be genetically influenced) or is capable of passing the condition on to their children (like color blindness). Technologies for evaluating DNA have become so good that millions of tests (millions of datapoints) can be generated in one attempt. Whatever it is, it is good to keep in mind that just because someone has an altered DNA in a gene being tested or if a result shows or tells that you are pre-disposed to a disease like cancer, it does not necessarily mean that someone is going to get the disease. There are certain ways genes work within our cells and a basic understanding of Genetics is necessary before you worry about getting a disease of any type. See Genetics, DNA and Genes before you do a genetic test so that you know how different results can be understood and appreciated. Also, if questions are there, it is best to talk to your family physician or find a genetic counselor near you. Most hospitals have them, and a list of Genetic Counselors in each State in the US can be found at the National Society of Genetic Counselors (NSGC) website:
Different types of genetic tests are done for different reasons. The reasons are described along with examples so that you can know how clinicians (doctors) might use these tests. What is listed below are tests that are mostly ordered by doctors.
In 1865, Gregor Mendel, the father of modern genetics described inheritance as an observable trait through experiments done on plants. By the 1930s, DNA was confirmed as the genetic material that was responsible for the traits being observed. The first breakthrough for DNA testing came about in the 1970s in the form of DNA sequencing. Then came the discovery of restriction enzymes. These are enzymes that cut DNA at specific sites. By the 1980s, many restriction enzymes were discovered that were able to cut at specific sequences. These enzymes were quickly used in a technique called Restriction Fragment Length Polymorphism (RFLP) analysis where the ability to cut or not cut at a site allowed the mapping of mutations. So, the first set of DNA tests were all based on this method. In the 1990s, Polymerase Chain Reaction (PCR) based DNA testing was introduced which allowed the use of small amounts of DNA as well as different types of samples (blood, tissue, biopsies, swabs etc.). PCR is a method that allowed amplification of DNA (see DNA Sequencing section on how DNA is amplified). Most of the time, DNA tests with PCR included the amplification of DNA followed by RFLP analysis. With DNA sequencing and other genotyping methods becoming more established, genetic tests started becoming popular and now covers a wide range of applications. For more information see:
Most doctor’s office will collect blood or some tissue sample (cheek cells or biopsies in serious cases) and send them to a laboratory. If you use a direct to customer home test kit, most will ask you to collect a saliva sample in a special collection tube. Some companies (like GenoTypica) will ask you to swab your cheek inside your mouth with a swab and send the swab in for testing, also in a special collection tube.
There is hardly any physical risk in collecting a sample, particularly if the sample is a cheek swab and you follow instructions that come with the kit. The goal is to get a good sample.
There is emotional risk if you receive unexpected results. Even if a test is ordered by a physician, once you get an unexpected result, it could be difficult. You may feel scared, angry or anxious. Also, there are financial risks. Some tests might cost thousands of dollars. If testing is ordered by a doctor, insurance may cover the cost. If testing is done by the DTC (direct-to-consumer) route, then it may be in the hundreds of dollars. Note that all genetic conditions may not be caught in the test and not all variations for a particular genetic disease may be detected in the test that was run. No test may be 100% accurate but most genetic tests done in hospitals and reputed companies will be close to 98% accurate and that is actually, very accurate. This does not mean that sample mix-up and other unexpected errors and omissions may not happen. So, it is always best to get a second opinion if you are not sure of the results or were not expecting the results that were received.
What is mentioned below is the typical format of a result. This does not mean all labs and all companies report results this way. Generally speaking, even if millions of data points are generated in a single effort for a variety of conditions; for a single test, a simple explanation may be provided by your doctor or genetic counselor as given below.
If a genetic test is done in a hospital lab or in a well managed and professional lab of a reputable company, certain standard guidelines are followed. These are standards that most labs follow and there are Federal as well as state standards. This also may mean that the test has been validated analytically and also clinically. In such cases, analytical validity looks at how accurately the lab can detect a specific mutation. Clinical validity means this mutation has been clinically established as being related to a specific disease or condition. Most if not all DTC tests are done with established methods (provided by vendors of the instrument systems used for testing) and validated markers (published papers), that accuracy is in the 98% to 99% rate. No test is 100% accurate and one should be skeptical if anyone makes such claims. Anything at or above 98% accuracy is considered sufficient in most clinical situations. Keep in mind that some of the OTC antigen testing kits that you can find in a pharmacy are only 80% accurate but are considered acceptable. DNA testing is almost all the time more precise and reliable.
Genetic tests (DNA tests) are useful and provide a lot of different types of information depending on what you are trying to do. From single gene tests to whole genome scans, from doctor ordered test to direct-to-consumer offerings, it can help you determine if you have a specific genetic condition or if you are likely to develop a genetically influenced condition. It has its benefits and it also comes with risks and limitations. If Genetic Testing of any type is of interest to you, it is best to start first with your healthcare provider. They can refer you to a genetic counselor who can provide you with a lot more information about all types of testing and how it can benefit you. Additionally, once you receive a test result or a test report, it is best to sit down with your genetic counselor and evaluate the information. No testing company can provide you or should provide you with directions on next steps. Genetic tests provide actionable information but you will need advice from a trained professional – your doctor or your genetic counselor. Most hospitals have them, and a list of Genetic Counselors in each State in the US can be found at the National Society of Genetic Counselors (NSGC) website: