What blood work is needed to diagnose measles and rubella?

Blood Work for Diagnosing Measles and Rubella

For accurate diagnosis of measles and rubella, specific serological testing is required, with IgM antibody testing being the primary diagnostic method for both diseases.

Measles Diagnostic Testing

Primary Diagnostic Tests

• Serum measles-specific IgM antibody testing is the most appropriate first-line test for confirming measles infection 1, 2
• The direct-capture IgM EIA method is recommended for its superior sensitivity and specificity 1, 2
• Blood should be collected during the first clinical encounter with a person who has suspected measles 1

Timing of Specimen Collection

• Measles IgM may be detectable at rash onset, peaks approximately 10 days after rash onset, and remains detectable for 30-60 days 1, 2
• IgM antibody testing is most reliable when collected 6-14 days after symptom onset 2
• If measles IgM is not detected in serum obtained within the first 72 hours after rash onset, a second specimen should be collected at least 72 hours after rash onset 1, 2

Alternative Testing Methods

• Paired acute and convalescent-phase serum specimens can demonstrate a significant rise in measles antibody titer 1
  • Acute-phase specimen: collect within 1-3 days after rash onset
  • Convalescent-phase specimen: collect approximately 2-4 weeks later
• Virus isolation from clinical specimens (urine or nasopharyngeal mucus) should be collected as close to rash onset as possible 1

Interpretation Considerations

• False-negative results may occur if specimens are collected too early (within first 72 hours of rash onset) 1, 2
• False-positive results can occur with parvovirus infection and should be confirmed with more specific testing methods 1, 2
• Persons with febrile rash illnesses who test negative for measles should be tested for rubella 1

Rubella Diagnostic Testing

Primary Diagnostic Tests

• Serum rubella-specific IgM antibody testing is the most commonly used method for serologic confirmation 1
• Blood for IgM testing can be obtained as early as 1-2 days after rash onset 1

Timing of Specimen Collection

• Rubella-specific IgM antibody becomes detectable shortly after rash onset, peaks at approximately 7 days, and remains detectable for 4-12 weeks 1
• If IgM is not detectable in the first specimen, a second specimen should be collected 5 days after rash onset 1

Alternative Testing Methods

• Paired acute and convalescent-phase serum specimens can demonstrate a significant rise in rubella antibody titer 1
  • Acute-phase specimen: collect as soon as possible after rash onset, preferably within 7 days
  • Convalescent-phase specimen: collect at least 10 days after the acute-phase specimen
• Virus isolation from clinical specimens is another diagnostic option, particularly for congenital rubella syndrome (CRS) 1

Interpretation Considerations

• False-negative rubella IgM results may occur even with appropriately timed specimens 1
• False-positive IgM results may occur with certain viral infections (e.g., infectious mononucleosis, cytomegalovirus, parvovirus) and in rheumatoid factor positive individuals 1

Emerging Diagnostic Methods

• Filter paper blood spots show high concordance with serum samples for both measles and rubella IgM and IgG detection (93-98% concordance) 3
• Saliva testing using antibody capture assays can detect virus-specific IgM in 92% of measles and 100% of rubella cases during the first week of illness 4
• RT-PCR testing of oral fluid has shown superior detection of rubella cases compared to IgM testing in the first 2 days after rash onset 5

Important Clinical Considerations

• Laboratory confirmation should be attempted for every suspected case of measles and rubella 1
• Immediate notification of local health departments is essential for suspected cases 1, 2
• Control activities should not be delayed pending laboratory results 1
• For congenital rubella syndrome, serologic confirmation can be obtained by testing cord blood for rubella-specific IgM antibodies 1

Diagnostic Algorithm

1. Collect serum specimen at first clinical encounter
2. Test for disease-specific IgM antibodies using direct-capture EIA method
3. If negative and collected <72 hours after rash onset, collect a second specimen
4. Consider paired acute/convalescent specimens for IgG testing if IgM results are inconclusive
5. For virus isolation/molecular testing, collect appropriate clinical specimens (nasopharyngeal, urine) as close to rash onset as possible 1, 2