Virus testing explained

Blood borne viruses like hepatitis and HIV are transferred via the blood or semen, which can occur through sharing injecting equipment, razors or tattooing needles, or engaging in unprotected sex. It is crucial that those in a high risk group, such as injecting drug users, get tested regularly but anyone can contract these viruses.

Why do you need to get tested?

• If you think you may have been exposed to the virus and are concerned that you may be infected
• If you have clinical symptoms and you need to confirm or exclude infection with Hep C, Hep B or even HIV as a causative agent. This will assist future treatment.

Why do you need to find out the result?

• Responsibility. When you know that you have an active infection, it is important that you take measures to protect your family and friends.
• If you have an active infection there are treatments that can clear the virus, slow its progression or manage the symptoms.

Which tests are available for Hep C and what do the results mean?

1. Primary antibody screening test

This will determine if you have been exposed to the virus

20% of people exposed to Hep C clear the virus completely from their body, but they still have antibodies to Hep C in their system. In this case, a reactive or weak positive antibody test would mean past exposure to the virus. The antibody test can remain reactive or weak positive for years after you have cleared the virus.

If you have been recently exposed to the virus but have a negative primary antibody test, it is recommended that you get tested again after a period of time. It can take up to three months for an antibody screening test to become positive following exposure to Hep C.

A reactive or weak reactive antibody test does not mean an active infection. The results need to be confirmed by a second test, which is usually a PCR test.

2. PCR test

This test will determine if you have an active Hep C infection

A negative PCR result means that there is no active Hep C infection. The virus has probably cleared even if the primary antibody test is positive. However, it is recommended that you get tested again after a period of time.

A positive PCR result means an active Hep C infection and the virus was not cleared during the acute stage of the infection. In this case you are at risk of the disease and can transmit the virus to someone else. It is recommended that you consult with a specialist.

Which tests are available for Hep B and what do the results mean?

Hepatitis B surface antigen test (HBsAg)

A reactive test to this antigen is an earliest indication of acute Hep B and frequently identifies infected people before symptoms appear. If you have an active infection you are at risk of transmitting the virus to others. We recommend that you see a specialist.

What is an HIV test and what do the results mean?

There are two types of HIV: HIV-1 and HIV-2. Both types are transmitted by sexual contact and through blood.

HIV antibody tests are the most appropriate test for routine screening. The most widely used test is the ELISA antibody test (enzyme-linked immunoabsorbent) also known as EIA (enzyme immunoassay).  Most people recently exposed to HIV develop detectable HIV antibodies within 6 to 12 weeks after exposure.

A reactive or weak positive test is an indication of exposure to the virus. A second antibody test is usually performed on a reactive or weak positive sample for confirmation.

If you have recently been exposed to the virus but your first antibody test is negative, it is recommended that you get testing again after a period of time. It can take up to three months for an antibody screening test to become reactive.

It is recommended that if you have a reactive or weak reactive test, you consult with a specialist.

Serological testing

This process establishes the presence of antibodies and antigens in bodily fluids, such as blood and oral fluid.

Serological testing either captures the antigens produced by bacteria or viruses during their replication in the body or identifies specific antibodies raised by the immune system against invading bacteria or viruses.

• Antigens are protein molecules released by the organism during its replication in the blood.
• Antibodies are protein molecules developed by the body’s immune system specifically to bind and neutralize viruses and bacteria.

A blood sample usually contains a high concentration of antigens or antibodies which will indicate the presence of an infection.

Serological testing uses a laboratory-based test called an ELISA. Enzyme-linked immunosorbent assay (ELISA), also known as an enzyme immunoassay (EIA) is a biochemical technique developed to detect and quantify the presence of antigens or antibodies in biological samples.

How does an ELISA test work?

An Enzyme-linked immunosorbent assay (ELISA) works by placing an antigen specific to the bacteria or virus on a ‘solid-phase surface’ and adding the sample to that surface. An enzyme-labelled antibody or conjugate is then added, and finally a substrate, which changes colour if the antigen of the bacteria or virus is detected.

Molecular biology testing

This is also known as Nucleic-acid-based testing (NAT). Molecular biology testing works by multiplying the DNA of the virus itself using a technique known as polymerase chain reaction (PCR).

A PCR is conducted in three stages, shown in the points below.

• Denaturation: The first stage is to heat the sample (called template DNA) so that the DNA of the virus splits from a double helix into two separate strands.
• Annealing: The second stage is to add DNA primers specific to the virus being detected. The primers bind to the single strands of DNA where they match up (e.g. ATG will bind to TAC).
• Extension: The third stage is to add DNA polymerase - an enzyme that copies the template DNA. DNA polymerase creates new strands of DNA by adding nucleotides (dNTPs) in the gaps between the primers.

These three stages are repeated about 20 times, each time copying the target DNA sequence again and again.  Once a significant number of copies are created there is enough of the virus’s DNA visible to make a diagnosis.

The advantage of PCR-based testing is its potential to quickly amplify very tiny amounts of DNA before the onset of the symptoms. However, it is important to recognize that PCR based methods are very sensitive to contamination and need to be interpreted with extreme caution.

Other BBV testing methods

What is genotype testing?

This is a molecular biology technique used to determine the sequence of genetic material. The main benefit of this technique is to establish various genetic subtypes and investigate viral mutations, i.e. how the virus or bacteria changes once it is in the body.

Viruses like HIV replicate rapidly during the course of infection and this causes changes in their genetic material. Determining subtype and monitoring viral mutation are essential for patients who are in treatment programme.

Genotyping technology is also used in epidemiological studies (looking at patterns of health and illness and associated factors) to help control spreading of diseases by tracing the origin of outbreaks.

What is viral load testing?

Viral load testing is used to measure the severity of the infection by calculating the number of virus particles in a given amount of blood. The result is usually given as virus copies per millilitre of blood plasma.

This particular test is an important part of the process of monitoring therapy effectiveness during the chronic stages of viral infection.

Please note: genotyping and viral load testing are not currently providing by Concateno.