How Scarlet Fever Is Diagnosed

Show Article Table of Contents

If you have concerns about scarlet fever but aren't sure how to get a diagnosis, a trip to your doctor can help. There are simple tests that a healthcare professional can do, such as a strep test or a culture, along with an examination, to determine if your symptoms are caused by scarlet fever or something else.

Scarlet fever diagnosis
© Verywell, 2018

Self-Checks/At-Home Testing

Scarlet fever is the presence of a rash on the body when you have an infection with Group A streptococcus bacteria causing a sore throat. Strep throat is the common name that is given for this infection. Scarlet fever simply means you or your child has a rash with strep throat.

Although this may seem like a simple thing that could be diagnosed at home, it is not. There is no accurate way to determine if you or your child has strep throat at home, despite claims that "white patches" in the throat indicate strep. This is simply not true.

White patches may be present in the throat with strep, but they may also be present when a sore throat is caused by other bacteria or viruses and a person can have strep with no white patches. So, it's best to visit a doctor to get a diagnosis.

Labs and Tests

A healthcare professional can perform quick, painless tests to confirm a scarlet fever diagnosis.

Rapid Strep Test

Rapid strep tests are—as the name suggests—very quick. Results are usually available in less than 10 minutes.

A swab is rubbed in the back of the oropharynx and then placed in a solution that indicates the presence, or lack of, the Group A strep bacteria. Although these tests are quick and convenient, they are not always 100 percent accurate.

Throat Cultures

Throat cultures are considered the gold standard for diagnosing scarlet fever and strep throat. The sample is obtained the same way as a rapid strep test—a swab that resembles a long Q-tip is passed over the back of the throat in the oropharynx. For this test, the sample is typically sent off to an outside lab where it is allowed to "grow" to determine if Group A streptococcus bacteria is present.

This test is more accurate but it takes longer, so many healthcare providers choose to use throat cultures as a backup diagnostic tool. Often, a throat culture will be sent off if a rapid strep test is negative or if a child has a history of many false negative or false positive strep tests.

Differential Diagnoses

A person with a sore throat and rash can have any number of illnesses. A vast majority of rashes and sore throats are caused by viruses. However, if you or your child has this combination of symptoms, it's important to see your healthcare provider for an accurate diagnosis—even more so if a fever is present as well.

The rash of scarlet fever typically begins in the creases of the body—the neck, underarms, and groin—and then spreads to the torso and the rest of the body. It may start off looking like large flat red bumps and then will change to the appearance of red sandpaper. The cheeks often have a rosy appearance as well. 

Children with scarlet fever or strep throat that are left untreated may develop rheumatic fever, but it is rare in adults. Another potential complication of these illnesses is post-streptococcal glomerulonephritis, which is a very complicated sounding name for an inflammation of the kidneys after an infection with Group A strep. Your doctor should be able to differentiate between all of these and provide appropriate treatment.

Was this page helpful?
Article Sources
  • Group A Strep | Scarlet Fever | GAS | CDC. https://www.cdc.gov/groupastrep/diseases-public/scarlet-fever.html. 
  • Group A Strep | Post-Streptococcal Glomerulonephritis | | PSGN | GAS | CDC. https://www.cdc.gov/groupastrep/diseases-public/post-streptococcal.html.