Diagnosis

Some children with MIS-C test negative for a current infection with the COVID-19 virus. This means they don't currently have the virus that causes COVID-19. Yet evidence indicates that many of these children were infected with the COVID-19 virus in the recent past, as shown by positive antibody test results.

An antibody test with a positive result means that the child's immune system developed blood proteins (antibodies) that fought the COVID-19 virus. Sometimes this blood test is the only indication that the child was ever infected — meaning that the child may have fought the infection without ever having signs or symptoms of COVID-19. Still, some children with MIS-C are currently infected with the virus that causes COVID-19. This is usually confirmed by detection of the virus on a swab taken from the back of the nose or throat.

In addition to doing antibody testing and a clinical assessment, doctors may order some of these tests to look for inflammation and other signs of MIS-C:

• Lab tests, such as blood and urine tests, including tests that look for an abnormal level of inflammatory markers in the blood
• Imaging tests, such as a chest X-ray, an echocardiogram, an abdominal ultrasound or a CT scan
• Other tests, depending on signs and symptoms

Inflammation can seriously affect the heart, blood vessels, kidneys, digestive system, brain, skin or eyes.

When doctors suspect MIS-C, they need to rule out active cases of COVID-19 as well as other inflammatory conditions such as Kawasaki disease, sepsis or toxic shock syndrome, for early diagnosis and proper treatment.