according to the Robert Koch Institute, Germany. If a patient has a fever and cough and feels exhausted, it could be COVID-19. What significance do rapid tests have? And when should doctors advise their patients about them?
When to Test
People at a higher risk for severe COVID-19 benefit from tests. This population includes the following groups:
- Older patients
- Immunocompromised patients
- Patients with respiratory diseases
- Patients with cardiovascular diseases
- Patients with liver and kidney diseases
- Patients with neurological diseases
- Patients with obesity
If doctors detect SARS-CoV-2 infection early, they can prescribe Paxlovid, for example, to reduce morbidity and mortality risks. Conversely, people without specific risks should test themselves if they plan to visit vulnerable individuals.
Detecting New Variants
A comprehensive study from the fall of 2022 provides evidence that antigen tests targeting the nucleocapsid (N) protein of SARS-CoV-2 also detect new variants.
The researchers built a library of various versions of the SARS-CoV-2 N protein. Their collection included nearly 8000 individual amino acid substitutions, representing more than 99.5% of all statistically possible mutations of the N protein.
They then examined how these N proteins interacted with 17 antibodies used in 11 commercially available antigen rapid tests.
All antibodies were able to recognize altered N proteins. Since the researchers successfully investigated diagnostic antibodies against nearly all possible N-protein mutations, rapid tests should be able to detect future virus variants. However, sensitivity and specificity may still change.
Test Timing
Uncertainty about what time of day to test can be mitigated by performing multiple COVID-19 rapid tests over time. The Food and Drug Administration (FDA) and similar organizations make this recommendation. Studies of symptomatic individuals show that serial tests increase accuracy.
In the early stages of infection, swabs may contain too little virus material because of widespread immunity against SARS-CoV-2. That is, they may contain inadequate levels of the relevant antigen. Especially in asymptomatic individuals or patients in the incubation phase, a single test may therefore yield a false-negative result. Therefore, the FDA recommends conducting at least two additional tests 48 hours apart in case of a negative test result.
Costs of Rapid Tests
The days of free tests are long gone. In Germany, the distribution of free preventive coronavirus tests was discontinued on March 1, 2023.
Test kits are still available in pharmacies or drugstores. In packages with 5-10 tests, the individual test costs between €0.90 and €1.50, depending on the provider. If a patient still has old rapid coronavirus tests in his or her medicine cabinet, are they still suitable?
Expired Tests
Properly stored tests that have not passed their expiration dates can still be used. But microbiologist and pathologist Daniel Rhoads, MD, from the Cleveland Clinic in Ohio warns against expired rapid tests.