A diagnosis of Hep C infection is not possible with a single test. Some tests are designed to be diagnostic tests to determine if a person has ever been infected with the hepatitis C virus (HCV) while others are used to monitor the status of the virus once a person has been diagnosed with HCV. These other tests are also used to monitor a person’s response to treatment. Further tests monitor how the virus is affecting the body. New tests are being developed to make the testing process faster and more accurate, but each province or territory in Canada selects the specific tests its labs will use, so there are differences across the country. Informed consent is an important part of the testing process.
Diagnostic Tests (to detect Hep C infection):
1. HCV antibody testing: These tests detect the presence of hepatitis C antibodies in the blood. A positive result indicates the person has antibodies to HCV and therefore has been exposed to the hepatitis C virus at some point in his or her life. However, the full status of hepatitis C infection cannot be known based on antibody testing alone. The person may have an active infection, meaning he or she has virus circulating in their body and are infectious, or an inactive infection, which means he or she has cleared the virus. It usually takes 6-9 weeks (but can take up to six months) after HCV infection for the body to make enough antibodies for the test to give a positive result. This time period is known as the window period. Some examples of antibody tests include enzyme linked immunoassay (EIA or ELISA) and recombinant immunoblot assay (RIBA).
2. RNA testing: These tests check for the genetic material of the virus (RNA) in the blood. They are generally used when a person has tested positive for HCV antibodies. They can measure the concentration of circulating virus in blood, like a viral load test (measured in IU/ml—international units per millilitre). This is important because some people are able to clear the HCV from their body without treatment and thus will have no detectable HCV RNA in their blood. The tests are also used to determine the genotype of the virus. This information is important when a person is thinking about starting Hep C treatment because some genotypes of the virus respond better to treatment than others.
Originally there were two versions of these tests—a quantitative one to count the amount of virus in the blood and a qualitative one to measure if the virus was detectable or undetectable. Current RNA testing is very sensitive and capable of detecting HCV RNA as low as 15 IU/ml. Although HCV RNA levels below 15 IU/ml are considered undetectable and likely mean that a person has successfully cleared the virus form their body, repeat testing in six months is important to be certain. Tests for detecting RNA in blood samples are often referred to as polymerase chain reaction (PCR) tests and are one of the most common versions of nucleic acid testing (NAT).
Monitoring Tests (to track liver damage):
1. biopsy: During a liver biopsy, a small piece of the liver is removed with a needle and then examined under a microscope. The sample is evaluated for the degree of scarring. Most systems for measuring damage use a scale from zero to four—with zero being no scarring and four being cirrhosis. Biopsy is an invasive procedure that requires a brief hospital visit (4–5 hours) and can result in severe but rare medical complications, caused by internal bleeding. A doctor will weigh the benefits and risks of this test before deciding the best course of action for the patient.
2. ultrasound: These tests measure liver scarring in a non-invasive way using sonography or elastography (which use sound waves or vibrations to create “maps” of body tissues). Though not as accurate as a biopsy these tests are faster and less painful for the patient and their popularity is growing for assessing liver damage.
3. liver enzyme tests: There are tests to measure liver enzyme levels in the blood. Liver damage leads to higher blood levels of liver enzymes (such as ALT and AST). This can be caused by any number of factors, including hepatitis viruses, chemicals, alcohol, medicines and other toxins. Sometimes, liver enzyme tests can flag that something is damaging the liver and alert a healthcare provider to do more testing, which can include testing for hepatitis C. Other liver enzymes include ALP, LDH and GGT.
4. liver function tests: The more damage the liver sustains, the less able it is to complete its 500-plus functions. There is a battery of tests that healthcare providers can use to check how well the liver is working. These include:
- prothrombin time or INR: prothrombin is a protein that is responsible for helping blood to clot
- bilirubin: this substance produces the yellow colour of jaundice and is produced when the liver breaks down old red blood cells
- albumin: a major blood protein, albumin is produced by the liver and is used in transporting some molecules through the body and maintaining fluid levels in the blood
These tests show up as abnormal only when the liver is badly damaged. Other conditions can affect these blood tests, such as diet or other viruses. A physician can interpret what the results mean.
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