Is a blood test useful if a COVID-19 infection is suspected?

A blood test can be useful in the context of COVID-19 infection, but it is not the primary diagnostic tool. Here are some situations in which a blood test can be useful.

A blood test can be used to detect antibodies to SARS-CoV-2, which can indicate whether a person has previously been infected with the virus. This type of test is useful in determining whether a person has had COVID-19 in the past, especially if the person had no symptoms or if the infection occurred a long time ago. However, it is not suitable for diagnosing an acute (current) infection.

Blood tests can be used to assess the immune response after vaccination or infection by measuring specific antibodies or other immune markers. In patients who are severely ill with COVID-19, blood tests can be used to measure certain biomarkers that indicate inflammation, organ damage, or clotting problems. Examples of such markers include D-dimer (for clotting), C-reactive protein (for inflammation), and liver or kidney function tests.

In some cases, a blood test can be useful to rule out other causes of symptoms or to determine whether there is a co-existing infection or condition.

For the diagnosis of an acute COVID-19 infection, the PCR test or an antigen test on a sample from the respiratory tract (e.g. via a nose or throat swab) remains the gold standard. These tests detect the presence of the virus itself and quickly indicate whether someone is currently infected.

Source: https://journals.asm.org/doi/full/10.1128/jcm.00512-20

Author: Prof. Dr. Dirk Devroey - Latest update: 2022-12-01 - Copyright: Clinifacts 2025