What is a Viral Load Test?

Mary McMahon

A viral load test is a medical test performed to determine how many copies of a virus are present in a patient's blood. This testing is used to collect information on the severity of an infection. Viral load testing is used in the diagnosis, treatment, and long term monitoring of patients with the human immunodeficiency virus (HIV), hepatitis B and C, and cytomegalovirus. Many labs have the capacity to process patient samples submitted for a viral load test.

The number of virus copies in a patients blood are determined through viral load tests.
The number of virus copies in a patients blood are determined through viral load tests.

Several different methods can be used to perform a viral load test. Once a method has been used, it is important to continue using the same method because readings can vary between methods. Switching back and forth between different methods will provide inconsistent results. This could endanger the patient or create false information about the patient's progress that might lead to bad medical decisions.

In the viral load test, a sample of body fluid like blood is analyzed and the number of copies of the virus are counted to return a value in terms of viral units per given unit of body fluid. High viral loads indicate more severe infections because there are more copies of the virus. Changes in the viral load can show patient progress. If the load decreases, it means that the patient is responding to medication. If it increases, the infection is growing worse and either the current treatment methods are not working or the patient is having difficulty complying with the treatment plan.

The most ideal test result is a low or undetectable result. It is important to be aware that undetectable results do not mean that the virus has been eradicated. Copies of the virus can still be present in the body, sometimes entangled in the cells instead of floating freely in body fluids like blood. Thus, a patient with an undetectable result has not been cured, but is responding very well to treatment. If the levels can be kept low or undetectable with medications and other treatments, the patient is likely to survive longer.

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When people are initially diagnosed with viral infections like HIV, a doctor will usually request a viral load count to create a baseline that will be used to monitor the patient over time. Subsequent tests will be used to monitor the course of treatment and to periodically reassess patients to confirm that their treatment is still effective. If a viral load test shows a change, doctor and patient can discuss a new course of treatment to address the change.

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