What is the difference between antigen and PCR testing for SARS-CoV2?

While a PCR test detects the genetic material of a virus, an antigen test detects the protein (the protein envelope) of the virus. However, today's topic is not concerned with the medical differentiation or processing of the procedure, but with the procedure and explanation of which test should be used and when. This blog post is about the difference between antigen testing and PCR testing and the question of when which test is appropriate in the current pandemic.

The Antigen Test

The antigen test or bedside test is a laboratory test and is performed directly on the patient in the presence of medical personnel. The antigen test is mainly used in health care settings such as hospitals, as it is helpful for a quick diagnosis and can provide meaningful results within 15 minutes. A nasopharyngeal swab is applied to a carrier medium and brought into contact with a test fluid. If the smear contains viruses, this is indicated by a line.

The best-known bedside test is used for blood grouping, but in times of the current pandemic it is used to determine the presence of a SARS-CoV2 infection.

For the use of an antigen test, it is important to show symptoms in relation to SARS-CoV2, as it is designed to confirm a clinical suspicion in a patient. Especially if no symptoms are present, this type of testing is unreliable.

Many SARS-CoV2 carriers have no detectable symptoms. In these cases, the use of an antigen test could be dangerous, as false negative results are often obtained and therefore false positives are given. This increases the risk of infecting other people despite a negative test result.

The PCR test

The PCR test (polymerase chain reaction) is a laboratory method, which is taken by nasopharyngeal swab or gargle method, but cannot be performed directly next to the patient. In this case an exact evaluation in the laboratory is necessary. This evaluation takes at least 4-5 hours (without logistics) and can also detect weakly positive, symptom-free infections. It can detect viruses in about 3 days before the outbreak of the disease and has a 99.5% certainty even in asymptomatic patients. In contrast to an antigen test, this test can also provide information about the exact viral load.

When which test?

It is important at which time and for which purpose the respective test is performed. If symptoms are present, an antigen test can be helpful, since it gives a quick result. If the test is positive, a PCR test is performed anyway to confirm the viral disease.

Example for practice

If you carry out preventive testing in your company to ensure the safety of your employees, we advise you to carry out regular PCR tests on the recommendation of our expert Assoc.-Prof.Dr.med. Christoph Steininger.

The explanation is quite simple. Ideally, only employees who feel healthy come to work. This does not mean, however, that they cannot be carriers of SARS-CoV2. If you decide to use antigen tests at your workplace, there is a risk of false negative test results, as these are very unreliable in asymptomatic infections. At the same time there is an increased risk of employees becoming infected and a corona cluster being triggered at their workplace.

A PCR test, on the other hand, can detect the virus without symptoms and much earlier than an antigen test, and offers more meaningful and reliable results.

Conclusion

Our expert Assoc.-Prof.Dr.med. Christoph Steininger sees the biggest problem in the fact that the antigen test is misused within this pandemic. It has its justification in many areas and is helpful in quickly confirming a clinical suspicion. However, it should not be used to confirm false positives by using it on asymptomatic individuals, as a PCR test is the proven safer option.

For reasons of better readability of this article, the language form of the generic masculine is used. This use of the male gender form should be understood independently of gender.