Hepatitis C is a chronic liver disease caused by the hepatitis C virus.

After exposure, it takes a week or two before there are enough virus particles to be detected in your blood. Your body responds to the virus by producing antibodies, but it can take anywhere from 3 to 12 weeks for antibodies to become detectable in your blood.

The time between exposure and when antibodies can be detected is called the window period.

Your doctor might test you for hepatitis C if you have symptoms or abnormal liver test results. A test taken during the window period can produce a false-negative result because antibodies aren’t detectable yet.

If you believe you’ve been exposed to the virus, your doctor will probably recommend taking another test in a month or two.

Hepatitis C is diagnosed by testing your blood. You may need to have more than one blood test.

Your doctor will take a sample of your blood from a vein in your arm. It’ll be sent to a lab for testing, and your doctor should be able to give you the results within a few days.

The initial test is to look for hepatitis C antibodies.

If you test negative and don’t believe you’ve been exposed to the virus, you probably don’t need another test. If there’s a possibility that you were exposed to the virus, and you’re still in the window period, the test should be repeated in a few months.

A positive result requires additional testing to determine if the antibodies are due to a past infection or a current one. If it’s a current infection, another blood test can tell you how much of the virus is in your bloodstream.

In the case of a hepatitis C infection, viral genotyping can help identify the specific type of hepatitis C to help guide treatment.

When a virus enters your body, your immune system takes action. It produces antibodies to seek out and destroy the foreign invaders. Once you make antibodies, you always have them, whether you have an active hepatitis C infection or not.

That’s where the antibody screening test comes in. After your blood is tested, the results will be negative (nonreactive) or positive (reactive).

A negative result means that you aren’t infected or that it’s simply too soon after infection to detect antibodies. Tell your doctor if you think you’ve been exposed within the previous three months. If you’re still within the window period, you’ll need to repeat the test to confirm the negative result.

A positive result indicates you have hepatitis C antibodies. That doesn’t mean you necessarily have hepatitis C, but it does mean you’ve been exposed to the virus at some point. You would still have antibodies even if your immune system defeated the virus.

Next, your doctor will likely order a qualitative blood test to determine if you have an active infection.

The qualitative RNA test checks your blood for particles of the hepatitis virus itself. This test is also called the polymerase chain reaction test.

A negative result means the virus hasn’t been detected in your blood. The antibodies from the previous test were from an earlier infection that was successfully cleared. You won’t need further testing.

A positive result means the virus has been detected and you have an active hepatitis C infection. Your doctor will probably order a quantitative test.

The quantitative RNA test measures how much of the virus you have in your system.

Your test will be reported in numbers. Less than 800,000 IU/L is a low viral load, and more is a high viral load. This can be helpful in choosing treatment and to monitor how well the treatment is working. The quantitative test doesn’t provide information about the health of your liver.

Learn more: Understanding hepatitis c viral load »

If you’ve tested negative, and you’re beyond the window period, you don’t need further testing. However, you should take steps to prevent contracting the virus in the future.

If you tested positive, keep in mind that about half of the people with hepatitis C don’t have health problems due to the virus. Some manage to clear the infection without treatment, and some benefit from drug therapy. For others, it becomes a slowly progressing disease.

There are six known genotypes and many subtypes of hepatitis C. Viral genotyping can determine the type so you get the appropriate treatment. Your doctor may also want to perform liver function tests before starting treatment.

Your doctor will explain all your test results and the pros and cons of potential treatments.

Keep reading: Hepatitis C treatment options »

You get hepatitis C when you come into contact with an infected person’s blood. Screening of blood in the United States keeps it from spreading during transfusions and organ transplants.

Hepatitis C can spread from mother to baby during childbirth or from a needle stick in a medical setting. It’s not common, but it can spread when you share personal items or during sexual contact with an infected person.

Here are some ways to lower your risk of hepatitis infection:

  • Don’t share needles, syringes, or other injection equipment.
  • Don’t share razors, toothbrushes, or other personal care items.
  • When getting a tattoo or body piercing, use only licensed facilities that take infection-control practices seriously.
  • Be very careful when cleaning up blood spills, and be sure to wear gloves. The hepatitis C virus can live up to three weeks on surfaces.
  • Practice safe sex.

The virus doesn’t spread through coughing, sneezing, breastfeeding, or casual contact.