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 (eg, outbreaks, international travel, etc.) in which transmission remains possible.
Quick Answers for Clinicians
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.
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 (eg, of an acute and convalescent sample) that demonstrates increased antibodies over time.
In regions where measles has been declared eliminated or is nearly eliminated, false-positive serology increases in frequency due to cross-reactivity with other more common infections that have similar symptoms (eg, rubella, parvovirus, or human herpesvirus 6). The CDC currently recommends the use of molecular detection, in addition to IgM serology, to improve diagnostic accuracy.
Indications for Testing
- Present with symptoms consistent with infection (eg, 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
Measles is primarily diagnosed using immunoglobulin M (IgM) serology and molecular detection (eg, 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 (eg, 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 (eg, within 0-2 days of rash onset) might impact serology.
The CDC recommends collecting serum and respiratory specimens (eg, 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 WHO Manual for the Laboratory-Based Surveillance of Measles, Rubella, and Congenital Rubella Syndrome for recommendations on specimen collection timing.
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
U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. For healthcare providers. [Last reviewed: Nov 2020; Accessed: Feb 2023]
U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. NNDSS: measles/rubeola 2013 case definition. [Last reviewed: Apr 2021; Accessed: Mar 2023]
Hübschen JM, Bork SM, Brown KE, et al. Challenges of measles and rubella laboratory diagnostic in the era of elimination. Clin Microbiol Infect. 2017;23(8):511-515.
World Health Organization. Measles: vaccine preventable diseases surveillance standards. [Published: Oct 2018; Accessed: Feb 2023]
U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. Genetic analysis of measles viruses. [Last reviewed: Feb 2022; Accessed: Mar 2023]