What blood tests can be used to diagnose mumps?

Blood Tests for Mumps Diagnosis

Laboratory confirmation of mumps requires mumps-specific IgM antibody testing as the primary serologic test, with viral PCR from buccal/parotid duct swabs or demonstration of a significant rise in IgG antibody titers between acute and convalescent sera as alternative confirmatory methods. 1, 2

Primary Serologic Testing

Mumps IgM Antibody

• Mumps IgM antibody testing is the preferred initial blood test for diagnosing acute mumps infection, as it indicates recent or current infection and is commercially available through immunofluorescence assays (IFA) or enzyme immunoassays (EIA). 1, 2
• IgM testing should be obtained within the first 9 days of symptom onset for optimal sensitivity, as concordance with RT-PCR is highest during days 2-5 post-onset and decreases thereafter. 3, 4
• A positive IgM result confirms acute mumps infection and does not require additional serologic testing. 5

Mumps IgG Antibody Testing

• A significant rise in mumps IgG antibody levels between acute and convalescent-phase sera (typically 2-3 weeks apart) confirms mumps infection when IgM testing is negative or unavailable. 1
• IgG testing results agree with RT-PCR/IgM results from post-onset days 3-10 onwards, making it useful for later-stage diagnosis. 4
• A single positive IgG result indicates past infection or vaccination (immunity) but does NOT diagnose acute infection—this requires either IgM testing or demonstration of rising titers. 1, 5

Alternative Laboratory Methods

Viral Detection

• Viral isolation from clinical specimens (saliva, buccal swabs, parotid duct swabs) or detection of mumps viral nucleic acid by RT-PCR provides definitive diagnosis. 1, 6
• Buccal or parotid duct swabs for PCR should be collected within 9 days of symptom onset, as viral shedding is highest during this period. 3
• Urine PCR remains positive for at least 5 days after oral detection and can serve as an alternative specimen source. 3

Neutralization Testing

• Focus reduction neutralization test (FRNT) showed 92.5% positivity in suspected mumps cases compared to 70.4% for IgM EIA and 83% for IgG EIA, with results agreeing with RT-PCR/IgM from the second week onwards. 4
• FRNT may be particularly useful in unvaccinated populations or when other serologic tests are equivocal. 4

Critical Diagnostic Considerations

Why Laboratory Confirmation is Essential

• Clinical diagnosis alone is unreliable—approximately one-third of clinically diagnosed mumps cases lack serologic evidence of actual mumps infection. 1, 2
• Parotitis has multiple infectious (EBV, CMV, HIV, influenza A, parainfluenza, adenovirus, enteroviruses) and noninfectious causes that mimic mumps. 2
• The CDC mandates laboratory confirmation for all suspected mumps cases to ensure accurate diagnosis and appropriate public health response. 2

Timing of Testing

• Collect specimens as early as possible after symptom onset—IgM sensitivity is highest in the first week, while viral detection methods are most successful within the first 3-5 days. 3, 4
• If initial IgM testing is negative but clinical suspicion remains high, repeat testing after 5-7 days or obtain convalescent IgG titers. 1

Special Populations

• In previously vaccinated individuals with breakthrough infections, viral detection methods (PCR) may be more reliable than IgM testing, as antibody responses can be attenuated. 5, 3
• Healthcare workers and outbreak settings require documented laboratory confirmation rather than clinical diagnosis alone. 1, 5

Common Pitfalls to Avoid

• Do not rely solely on clinical diagnosis—this leads to misdiagnosis in one-third of cases and prevents accurate disease surveillance. 1, 2
• Do not interpret a single positive IgG result as evidence of acute infection—this only indicates immunity from past infection or vaccination. 5
• Do not delay specimen collection—viral shedding and IgM detectability decrease significantly after the first week of illness. 3, 4
• Do not assume negative IgM rules out mumps in vaccinated individuals—consider PCR testing in these cases. 5, 3