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Measles - Rubeola. ARUP Consult®. Retrieved May 30, 2025, https://arupconsult.com/content/measles-virus

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Measles - Rubeola

Last Literature Review: September 2024 Last Update:

Medical Experts

Contributor

Slev

Patricia R. Slev, PhD, D(ABCC)
Patricia R. Slev, PhD, D(ABCC)
Professor of Pathology (Clinical), University of Utah
Section Chief, Immunology; Medical Director, Immunology Core Laboratory, ARUP Laboratories
Contributor

Measles is a highly communicable respiratory disease characterized by symptoms such as fever, malaise, cough, conjunctivitis, coryza, Koplik spots, and a maculopapular rash that radiates downward from the head. Although measles is currently classified as eliminated within the United States, there are certain contexts (e.g., outbreaks, international travel, etc.) in which transmission remains possible. When measles is suspected, serology and molecular detection are used for diagnosis. Serology is also useful to assess immunity. 

Quick Answers for Clinicians

Is laboratory testing required to confirm measles?

According to the CDC’s case definition for measles, a positive laboratory result in either an existing or epidemiologically linked case is required to confirm a measles diagnosis. For specific details, refer to the CDC’s case definition for measles. 

How does recent or previous vaccination affect testing for measles?

Although unlikely, it is still possible for measles-vaccinated individuals to develop infection. Measles infection in vaccinated individuals is typically milder, and immunoglobulin M (IgM) antibodies may be low or undetectable. In those who are vaccinated, suspected measles infection can be confirmed by molecular detection or paired IgG serology (e.g., of an acute and convalescent sample) that demonstrates increased antibodies over time. 

How does measles elimination affect the reliability of serology?

In regions where measles has been declared eliminated or is nearly eliminated, false-positive serologic test results increase in frequency due to cross-reactivity with other more common infections that have similar symptoms (e.g., rubella, parvovirus, or human herpesvirus 6). ,  The CDC currently recommends the use of molecular detection, in addition to immunoglobulin M (IgM) serology, to improve diagnostic accuracy. 

How can laboratory testing be used to differentiate between a measles vaccination-related rash and wild-type measles virus infection?

Following vaccination for measles, a small percentage of individuals may develop a postvaccination rash that appears similar to measles infection.  As individuals with a postvaccination rash are not infectious, being able to distinguish between vaccine reactions and infections with wild-type virus is critical. Molecular tests designed to specifically detect the vaccine strain of measles virus have been developed to help clinicians assess a patient’s risk. 

Measles virus sequencing (i.e., genotyping) can also distinguish between wild-type virus infection and a rash caused by a reaction to the measles vaccine strain virus. Genotyping may help with disease surveillance and tracking outbreaks.  These tests are available through local and state public health laboratories and the CDC.

Indications for Testing

Laboratory testing for measles is indicated in individuals who :

  • Present with symptoms consistent with infection (e.g., febrile illness culminating in a maculopapular rash), especially after international travel or exposure to measles or a measles-like illness
  • Require presumptive evidence of immunity

Laboratory Testing

Diagnosis

Measles is primarily diagnosed using immunoglobulin M (IgM) serology and molecular detection (e.g., by reverse transcription polymerase chain reaction [RT-PCR]). 

False-positive serologic results are more likely in regions where measles has been eliminated, due to cross-reactivity with other more common viruses (e.g., rubella, parvovirus, or human herpesvirus 6). ,  Molecular detection (available through many state-run laboratories and the CDC ) is useful to support diagnostic accuracy, such as when the timing of specimen collection (e.g., within 0-2 days of rash onset) might impact serology. 

Specimen Collection

The CDC recommends collecting serum and respiratory specimens (e.g., throat swab, nasopharyngeal swab/aspirates) during the first visit with any patient who has symptoms consistent with measles. When possible, a urine sample should also be collected.  Refer to the World Health Organization’s recommendations on specimen collection timing in Measles: Vaccine-Preventable Diseases—Surveillance Standards. 

Confirmation of Immunity

When vaccination status is unknown or evidence of immunity is required, IgG serology can be used to assess immunity. The CDC recommends measles vaccination for any individual with negative or equivocal test results. 

ARUP Laboratory Tests

Serology

References