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Genetic Test

Test Overview

A genetic test checks the DNA of your cells. It can find changes in your genes, or it can check the number, order, and structure of your chromosomes. Testing may be done on samples of body tissue, blood, or other body fluids such as urine or saliva.

You inherit half of your genetic information from your mother and the other half from your father. Genes determine things such as your blood type, hair color, and eye color, as well as your risk for certain diseases. Testing can find gene or chromosome changes that may cause medical problems.

Why It Is Done

This test may be done to:

  • Find out if you carry a gene for an inherited disease, such as Tay-Sachs disease or cystic fibrosis. This is called carrier identification. In families that have these diseases, some people don't get the disease, but they carry a gene change that they could pass on to their children. Finding out if you're a carrier can help you make decisions about having children.
  • Find out if your fetus has a genetic disorder or birth defect such as Down syndrome. This is called prenatal testing. It can help you make decisions about your pregnancy.
  • Check your baby for certain diseases, such as PKU. This is called newborn screening. This information can help guide treatment if your baby has a disease.
  • Find out if you carry a gene that increases your risk for a disease later in life, such as breast cancer or Huntington disease. This is called late-onset disease testing. This may be important if a close relative has such a disease. The information might help you take steps to prevent the disease. Or it can help you make decisions about having children.
  • Find out if you have an inherited heart disease called hypertrophic cardiomyopathy. You may want to have this test if a close relative has the disease.
  • Check for genetic changes that may affect your treatment. Testing may help your doctor find out if a blood thinner will work for you. Or it can help your doctor suggest the best treatment for a disease such as HIV or some cancers.

How To Prepare

You do not need to do anything special to prepare for this test.

Talk with your doctor if you have any concerns about the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form (What is a PDF document?).

The information found by a genetic test can have a huge impact on your life. So before you have the test, you may want to talk to a genetic counselor or a doctor who specializes in genetics (geneticist). Genetic counseling can help you understand your genetic risks and decide if you want testing.

How It Is Done

A genetic test can be done using almost any cell or tissue from the body.

Blood sample from a heel stick

For newborn testing, the blood sample is usually taken from the baby's heel instead of a vein. The health professional doing the heel stick will:

  • Clean your baby's heel with alcohol. Then he or she will prick the heel with a sharp tool called a lancet.
  • Collect several drops of blood inside circles on a special piece of paper.
  • Put a small bandage on the site.

Blood sample from a vein

The health professional taking a sample of your blood will:

  • Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
  • Clean the needle site with alcohol.
  • Put the needle into the vein. More than one needle stick may be needed.
  • Attach a tube to the needle to fill it with blood.
  • Remove the band from your arm when enough blood is collected.
  • Put a gauze pad or cotton ball over the needle site as the needle is removed.
  • Put pressure on the site and then put on a bandage.

Cell sample from a fetus

Cells are collected using amniocentesis or chorionic villus sampling.

To learn more, see:

How It Feels

Blood sample from a heel stick

Your baby may feel a little discomfort when the skin is pricked.

Blood sample from a vein

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

Saliva, urine, or semen sample

It is not painful to collect a saliva, urine, or semen sample.

Risks

Blood sample from a heel stick

There is very little chance of a problem from a heel stick. A small bruise may form at the site.

Blood sample from a vein

There is very little chance of a problem from having a blood sample taken from a vein.

  • You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
  • In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. You can use a warm compress several times a day to treat this.

Saliva, urine, or semen sample

Collecting a saliva, urine, or semen sample does not cause problems.

Other risks

The information from a genetic test can affect you and your family in many ways. For example, it may have an impact on:

  • Your emotions and relationships. You may feel anxious or depressed if you learn that you are likely to have a serious disease or have a child who has a disease. This news may also affect your relationship with your partner or other family members.
  • Your treatment choices. If you test positive for a disease-specific gene change (mutation), you may decide to use preventive or treatment options, if they are available. They can help to reduce the impact or severity of the disease. While many treatment options have been proven to work well, others may be harmful or may not work.
  • Your pregnancy decisions. Genetic testing can help you make decisions about your pregnancy or plan for the future. If you find out that your fetus has a genetic disease, you may decide to end the pregnancy. Or you may change your delivery plans. If your baby is likely to need special care after birth, you may need to deliver in a hospital that can provide this care.
  • Your privacy. Many people worry that their genetic information might affect their job options or their ability to get insurance. But the United States has a law called the Genetic Information Nondiscrimination Act of 2008 (GINA). GINA helps protect people who have DNA differences that may affect their health. But it has some limits. For example, this law doesn't apply to life insurance, disability insurance, or long-term care insurance. And it doesn't protect people who work for companies with fewer than 15 employees.

Genetic counseling is recommended before you have genetic testing. It can help you understand and make decisions about testing.

Results

A genetic test checks the DNA of your cells. It can find changes in your genes, or it can check the number, order, and structure of your chromosomes.

The results of genetic testing depend on the type of test done. Genetic testing may be used to:

  • Find out if your fetus has a genetic disease or birth defect.
  • Find out if you have an inherited disease.
  • Give information about how likely it is that you will have a disease in the future.
  • Find out if you are a carrier of a genetic disease.
  • Help choose the right treatment for some diseases, such as HIV infection or some types of cancer.

What Affects the Test

You may not be able to have the test, or the results may not be helpful, if you have a blood transfusion within a week before the test.

What To Think About

The information found by a genetic test can have a huge impact on your life. So before you have the test, you may want to talk to a genetic counselor or a doctor who specializes in genetics (geneticist). Genetic counseling can help you understand your genetic risks and decide if you want testing.

  • A prenatal test may find a serious inherited disease or disorder (such as Down syndrome). This would greatly impact both you and your child. You may want to think ahead to what you might do if the test finds a serious problem.
  • The results of the test are protected under the Health Insurance Portability and Accountability Act (HIPAA). HIPAA requires that providers, such as doctors, nurses, and hospitals, keep your health information private. Your privacy should be maintained, and your information should only be released to those who are authorized to have it.
  • Finding out that you have a genetic disease should not affect your ability to get a job or get health insurance. In the United States, there is a law called the Genetic Information Nondiscrimination Act of 2008 (GINA). It helps protect people who have DNA differences. But it has some limits. For example, this law doesn't apply to life insurance, disability insurance, or long-term care insurance. And it doesn't protect people who work for companies with fewer than 15 employees.
  • A genetic test can sometimes reveal information you didn't expect, such as whether a child's father is actually the biological father.

There are other types of genetic tests that you might want to think about. For example:

  • A karyotype test can be used to check the size, shape, and number of chromosomes. Extra or missing chromosomes, or abnormal positions of chromosome pieces, can cause problems with a person's growth, development, and body functions. To learn more, see the topic Karyotype Test.
  • A breast cancer (BRCA) gene test is done to check your risk of getting breast cancer. To learn more, see the topic Breast Cancer (BRCA) Gene Test.

References

Other Works Consulted

  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
  • Skirton H, Patch C (2009). Genetics for the Health Sciences: A Handbook for Clinical Healthcare, 2nd ed. Oxfordshire, UK: Scion Publishing.

Credits

ByHealthwise Staff
Primary Medical Reviewer Kathleen Romito, MD - Family Medicine
Martin J. Gabica, MD - Family Medicine
E. Gregory Thompson, MD - Internal Medicine
Elizabeth T. Russo, MD - Internal Medicine
Adam Husney, MD - Family Medicine
Specialist Medical Reviewer Siobhan M. Dolan, MD, MPH - Reproductive Genetics

Current as ofFebruary 23, 2018

Current as of: February 23, 2018

Author: Healthwise Staff

Medical Review: Kathleen Romito, MD - Family Medicine & Martin J. Gabica, MD - Family Medicine & E. Gregory Thompson, MD - Internal Medicine & Elizabeth T. Russo, MD - Internal Medicine & Adam Husney, MD - Family Medicine & Siobhan M. Dolan, MD, MPH - Reproductive Genetics