Is there a test for diagnosing measles?

Diagnostic Testing for Measles

Yes, measles can be diagnosed through serologic testing for measles-specific IgM antibodies, which is the preferred rapid diagnostic method, along with confirmatory testing through viral isolation or PCR when available. 1

Primary Diagnostic Approach

Serologic Testing - IgM Detection

• Enzyme immunoassay (EIA) for measles-specific IgM antibodies is the most suitable test for rapid diagnosis of measles infection and can be performed on a single serum specimen obtained soon after rash onset. 1
• IgM antibodies become detectable 1-2 days after rash onset, peak at approximately 7-10 days, and typically become undetectable within 30-60 days after acute infection. 1
• The optimal timing for IgM testing is within the first few days after rash onset, though sensitivity may be lower on the day of rash onset (58.3% detection rate). 2

Important Diagnostic Caveats

• In vaccinated populations, IgM may be detected in only 66.6% of acute-phase sera, increasing to 89.2% in convalescent sera, so a negative acute-phase IgM does not rule out measles. 2
• If acute-phase IgM is negative but clinical suspicion remains high, convalescent serum should be tested 2-4 weeks later. 2
• In low-prevalence settings where measles is rare, false-positive IgM results become more likely, and confirmatory testing using a more specific direct-capture IgM EIA method should be performed when there is no epidemiologic linkage to a confirmed case. 1

Alternative Diagnostic Methods

Paired Serologic Testing

• Measles can be confirmed by demonstrating a significant (four-fold or greater) rise in measles-specific IgG antibody titers between acute-phase (collected 1-3 days after rash onset) and convalescent-phase (collected 2-4 weeks later) serum specimens. 1, 3
• This method has been largely supplanted by single-specimen IgM assays but remains useful when acute IgM testing is negative. 1

Viral Detection Methods

• Measles virus can be isolated from clinical specimens (urine or nasopharyngeal mucus) or detected by reverse transcriptase-PCR, with specimens ideally collected as close to rash onset as possible. 1, 3
• Delay in specimen collection significantly reduces the likelihood of successful viral isolation. 1
• Molecular characterization of measles virus isolates is important for epidemiologic tracking but cannot be used for acute diagnosis due to the time required. 1

Clinical Context and Coordination

Immediate Public Health Notification

• Local or state health departments should be contacted immediately when measles is suspected, as one confirmed case represents an urgent public health situation requiring prompt investigation. 1
• State public health laboratories have been trained by CDC to perform measles serologic testing. 1
• Clinicians should contact their health department for guidance on collecting and shipping specimens for viral isolation. 1

Laboratory Test Selection

• Laboratories that regularly perform measles antibody testing provide the most reliable results due to standardized reagents and procedures. 1
• Multiple assay types are available including EIA (most common), latex agglutination, immunofluorescence assay, passive hemagglutination, and virus neutralization tests. 1