Learn How Genetic Testing Works Step by Step

What Genetic Testing Is and Why People Use It

Genetic testing is a medical procedure that examines your DNA to look for specific genetic changes, mutations, or variations. DNA is the instruction manual for your body—it controls everything from your eye color to how your cells work. A genetic test can reveal information about your genes that might matter for your health, ancestry, or family planning decisions.

According to the National Human Genome Research Institute, millions of genetic tests are performed each year in the United States. People pursue genetic testing for several reasons. Some want to understand disease risk—for example, a woman in her 30s might get tested if breast cancer runs in her family. Others are pregnant or planning pregnancy and want to know if their baby might have certain genetic conditions. Some people use genetic testing to confirm a diagnosis when they already have symptoms. Others are curious about their ethnic background or family history.

Genetic testing has become more common and more affordable over the past two decades. In the early 2000s, sequencing an entire human genome cost millions of dollars. Today, certain genetic tests cost less than $200. This drop in price has made testing more available to more people, though not all tests are covered by insurance.

It's important to understand that genetic testing is not the same as a regular blood test. A regular blood test might check your cholesterol or blood sugar. A genetic test looks at the actual structure of your genes to spot differences that have existed since birth or that might run in your family.

Practical Takeaway: Genetic testing examines your DNA to find information about disease risk, ancestry, or genetic conditions. Understanding why you might want a test and what it can show is the first step in learning how the process works.

The Main Types of Genetic Tests and What Each One Does

There are several categories of genetic tests, and each one serves a different purpose. Understanding the differences helps you know what to expect and what kind of information you might receive.

Diagnostic Testing is used when someone already has symptoms of a genetic condition. A doctor might order this test to confirm or rule out a specific diagnosis. For example, if a child shows signs of cystic fibrosis, a diagnostic test can confirm whether that's actually the condition by looking for known mutations in the cystic fibrosis gene.

Predictive or Risk Testing is for people without symptoms but who want to know if they carry genes linked to future disease. These tests are common in families with a history of conditions like Huntington's disease, hereditary breast cancer (BRCA1 and BRCA2 genes), or hereditary heart disease. A person might test negative, meaning they don't carry the mutation, or positive, meaning they do. A positive result doesn't always mean you will develop the disease—it means your risk is higher than average.

Carrier Testing checks whether you carry one copy of a gene mutation that could cause disease if passed to your children. You might not have any symptoms, but if both parents carry the same recessive mutation, their child has a 25% chance of inheriting the condition. Carrier testing is common before pregnancy and is especially relevant for certain ethnic groups. For example, Ashkenazi Jewish populations have higher rates of BRCA1 and BRCA2 mutations and Tay-Sachs disease.

Newborn Screening happens in hospitals within days of birth. All 50 U.S. states screen newborns for certain genetic and metabolic conditions. The test can catch disorders like sickle cell disease, phenylketonuria (PKU), and hypothyroidism early, when treatment can prevent serious problems or even death.

Pharmacogenetic Testing looks at how your genes affect the way you respond to medications. The FDA has cleared pharmacogenetic tests for about 300 drugs. For instance, certain genetic variations affect how quickly your body breaks down warfarin (a blood thinner) or codeine (a pain medication). Knowing your genetic makeup can help doctors choose the right dose.

Ancestry and Direct-to-Consumer Testing is marketed to the general public. These tests examine your DNA to estimate your ethnic background and connect you with relatives who have also taken the test. Companies like AncestryDNA and 23andMe fall into this category. While these tests can be informative, they're not diagnostic and shouldn't be used to make health decisions without talking to a doctor.

Practical Takeaway: Different genetic tests serve different purposes—some confirm current symptoms, some predict future risk, and some provide ancestry information. Knowing which type of test you need depends on your situation and why your doctor (or you) thinks testing makes sense.

Step-by-Step: How the Genetic Testing Process Works

The genetic testing process typically follows a consistent path from start to finish. Understanding each stage helps you know what to expect and what happens to your sample along the way.

Step 1: Ordering the Test Most genetic tests require an order from a healthcare provider—a doctor, nurse practitioner, genetic counselor, or physician assistant. The provider discusses why testing is being considered, what it might show, and what limitations exist. Some direct-to-consumer tests can be ordered online without a provider's order, but this approach bypasses professional guidance about what the results mean.

Step 2: Pre-Test Counseling Before testing, particularly for predictive or carrier tests, a genetic counselor often meets with you (by phone, video, or in person). Genetic counselors have specialized training and certification. According to the National Society of Genetic Counselors, there are over 4,000 certified genetic counselors working in the United States. They explain what the test does and doesn't do, discuss possible results and what each might mean, and address concerns or questions. This step is crucial for understanding informed consent.

Step 3: Providing Your Sample For most genetic tests, you provide a saliva sample or a blood sample. Saliva collection is simple—you spit into a tube or container. Blood is drawn by a phlebotomist (a trained person who draws blood) at a clinic, doctor's office, or lab. Some tests use a cheek swab. The sample is labeled with your name and a unique identifier number. For newborn screening, blood is collected from the baby's heel and spotted onto a special paper card.

Step 4: Sample Transport and Processing Your sample is placed in a secure container and sent to a certified laboratory. The lab verifies that the sample is adequate and processes it according to the test type. This stage can take anywhere from a few days to several weeks, depending on the test complexity and lab workload.

Step 5: Laboratory Analysis The lab examines your DNA using different technologies depending on the test type. For carrier screening or single-gene tests, the lab might use a targeted approach that looks only at specific genes. For broader tests, the lab might sequence larger sections or even your entire genome. The lab looks for specific mutations, deletions, duplications, or variations that have been linked to the condition being tested.

Step 6: Quality Control and Verification Results are checked multiple times to ensure accuracy. If results are uncertain or important to a major health decision, the lab might run the test a second time or use a different method to confirm findings. Some variants require additional verification through Sanger sequencing, a more targeted and precise method.

Step 7: Results Interpretation and Report Generation The lab creates a written report that explains the findings. Reports vary in format but typically include an overview, the specific variants found (or not found), and technical explanation. The lab may classify results as "positive," "negative," "uncertain," or "variant of uncertain significance" (VUS). A VUS means the lab found a change that is rare or not fully understood yet—it doesn't clearly mean disease or health.

Step 8: Receiving Results Results are typically reported to your healthcare provider first, not directly to you. Your provider may schedule a follow-up visit or call to discuss what the results mean for your health. This is where your provider's interpretation and guidance matter greatly. For some direct-to-consumer tests, results go directly to you online, though the company may also provide access to genetic counselors or doctors for interpretation.

Step 9: Post-Test Counseling After receiving results,