Investigations
1st investigations to order
measles-specific IgM and IgG serology (ELISA)
Test
Blood test identifying measles-specific IgM indicates acute infection.[34] Sensitivity is highest 3 to 14 days after rash onset.[35] Presence of IgG indicates an infection occurring sometime in the past or prior vaccination. Sensitivity is 83% to 92% and specificity is 87% to 100%.[36]
Rubella and parvovirus B19 infection may cause false-positive IgM ELISAs.
Result
positive
oral fluid
Test
In the UK, oral fluid is the preferred sample for measles surveillance and should be taken from all patients with suspected measles.[37] Oral fluid can be tested for IgM, IgG, and measles RNA.
Result
positive
Investigations to consider
acute and convalescent sera for measles-specific IgG
Test
Paired acute and convalescent sera can be used to detect a rise in IgG antibody by haemagglutination inhibition, complement fixation, ELISA, or fluorescent antibody detection. Confirmation results from detection of 4-fold rise in IgG antibody titre.[34] Useful if initial IgM test is not informative. Convalescent titres are drawn 3 to 4 weeks after acute titres.
Result
≥4-fold rise in antibody
measles RNA detection by PCR
Test
Measles RNA can be detected by polymerase chain reaction (PCR) from oral fluid, throat, or nasopharyngeal swabs or urine samples.[34] Best yield is obtained when samples are collected on days 1 to 3 of the rash, but virus still may be detected up to 10 to 14 days after rash onset.[38]
Result
positive
antigen detection by fluorescent antibody or PCR techniques
Test
Targets antigen detection. Labour-intensive; usually restricted to research laboratories.
Result
positive
isolation of virus in tissue culture system
Test
Labour-intensive; usually restricted to research laboratories.
Result
Positive
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