Diagnosis

Streptococcus rapid test

Definition - What is a rapid strep test?

Streptococci belong to the cocci family and characterize a group of gram-positive bacteria. A so-called streptococcal rapid test is used to diagnose an infection of the upper respiratory tract with streptococcal bacteria of serotype A.

The advantage of such a diagnostic procedure is that the quick test can be carried out easily and quickly by the person concerned at home.

Indications for a rapid test

If there is a suspicion of an infection with group A streptococci, a rapid test offers an initial detection of these bacteria. Group A streptococci are beta-hemolytic streptococci, which are also known as "Streptococcus pyogenes"Are designated.

These types of streptococci lead to the complete destruction of red blood cells (complete hemolysis) when infected. Typical infectious diseases caused by Streptococcus pyogenes are scarlet fever, tonsillitis or red rash.

What can I not test with the rapid test?

The test does not differentiate between streptococci that have an asymptomatic course of the disease and those with a pronounced clinical picture. In addition, the test can give false negative results if the antigen concentration is still very low in a fresh infection.

In both cases, a bacterial culture can be created from the sample. False positive results can also occur, even if this is very rarely the case. Such results come about when the throat swab is colonized with excessive amounts of the bacterial species Staphylococcus aureus.

Another aspect that the rapid test cannot detect are infections of the respiratory tract caused by other types of bacteria or other types of streptococci than type A.

Can I get it at the pharmacy without a prescription?

Rapid streptococcal tests can easily be purchased from pharmacies without a prescription. The costs here amount to 15 to 30 euros depending on the manufacturer.

Can you do this at home?

The test can be purchased at the pharmacy and simply carried out at home. If the test result is positive or symptoms persist, a doctor should be consulted at the latest.

execution

The rapid test contains a cassette with an integrated membrane. This is coated with rabbit anti-strep A antibodies in the test line area and with goat anti-rabbit antibodies in the control line area. There is also a pad with colored, gold-conjugated, polyclonal rabbit anti-Strep-A antibodies at the beginning of the membrane.

First of all, any Strep A antigens that may be present are removed from the throat swab sample using extraction reagents 1 and 2. This smear is then given on the test. In the presence of a streptococcal A infection, the sample migrates to the anti-strep A antibodies in the test line region and these turn pink.

If the test result is negative, this color reaction does not occur. The control line will also turn pink, regardless of whether there is a Strep A infection and thus Strep A antigens in the throat swab sample. The formation of this control line makes the test valid. The test result can usually be read within 8 minutes.

evaluation

A positive test result indicates an infection with beta-hemolytic streptococci type A. However, this does not yet constitute proof. For proof of an infection, a bacterial culture must be set up in which the bacteria are first multiplied and then analyzed or identified.

A negative test result usually indicates that there is no current streptococcal A infection, but an infection cannot be completely ruled out. Because a negative test result can also arise if the concentration of the bacteria is below the detection threshold of the test system.

How reliable is the test?

The streptococcal A rapid test usually has a sensitivity of 86% and a specificity of 95%. Sensitivity means the ability of the test to correctly identify sick people with an infection.

The term specificity means the ability of the test to correctly identify healthy individuals with no presence of Strep A infection. As already mentioned, a false positive result occurs when the test strip is colonized with large amounts of the bacterial species Staphylococcus aureus.

Duration

It takes a few minutes to perform a rapid test for Strep A infection. After applying the swab sample to the test cassette, the test result should be read within 8 minutes. The test should not be read after more than 10 minutes.

costs

The cost of purchasing a streptococcal A rapid test is between 15 and 30 euros.

Will the health insurance take care of that?

These tests are not a service of the statutory health insurance, so they have to be paid for privately.

What are the alternatives?

If you do not want to perform a rapid Strep-A test, you should definitely consult a doctor if you suspect an infection with the bacterium. This can create a bacterial culture, with which the bacteria can be multiplied on a special nutrient medium and then identified.

In addition, evidence of anti-streptolysin-O antibodies (ASLO) in the blood and anti-streptococcal DNAse B (antibodies against the enzyme "DNAse B" produced by Streptococcus pyogenes) can be requested from the laboratory.