From the Guidelines
Measles can be identified through various tests, including a blood test that detects measles-specific IgM antibodies, which is the most common diagnostic method. These tests are crucial for confirming the diagnosis, especially in patients presenting with characteristic symptoms like high fever, cough, runny nose, red eyes, and the distinctive rash that starts on the face and spreads downward. According to the study by 1, serologic diagnosis of measles can also be confirmed by a significant rise in antibody titer between acute- and convalescent-phase serum specimens, although this method has been largely supplanted by IgM assays. Some of the key tests for identifying measles include:
- Blood tests to detect measles-specific IgM antibodies
- PCR (polymerase chain reaction) testing on respiratory specimens, urine, or blood to detect measles virus RNA
- Viral culture from throat swabs, nasal specimens, or urine samples, though this takes longer to yield results
- Comparison of antibody levels from acute and convalescent phase serum samples to confirm recent infection by showing a rise in measles-specific antibodies. Early diagnosis through these tests is vital for implementing appropriate isolation measures, given that measles is highly contagious and can spread rapidly among unvaccinated individuals, as noted in the context of vaccine use and strategies for disease control 1.
From the Research
Laboratory Diagnostic Methods for Measles
There are several laboratory diagnostic methods that can be used to identify measles, including:
- Indirect detection via antibody (IgM and IgG) detection methods 2
- Direct detection by viral culture or viral genome detection 2
- Reverse transcription polymerase chain reaction (RT-PCR) methodologies 2, 3
- Enzyme-linked immunosorbent assay (ELISA) kits 4, 5
Sensitivity and Specificity of Diagnostic Methods
The sensitivity and specificity of these diagnostic methods can vary, with:
- IgM detection showing highest sensitivity when serum samples are collected ≥5 days after rash onset 3
- Virus isolation giving the highest sensitivity when samples are collected ≤3 days after rash onset 3
- RT-PCR showing a high positive rate with serum samples collected ≤3 days after rash onset 3
- Pooled sensitivity and specificity of all measles IgM detection methods being 0.94 (CI: 0.90-0.97) and 0.94 (CI: 0.91-0.97), respectively 5
Challenges and Considerations
There are challenges and considerations when using these diagnostic methods, including:
- Reduced positive predictive value of routine serological methods in areas with low prevalence due to high vaccine uptake 2
- Need for confirmation by other methods in areas with low prevalence 2
- Potential for false-positive and false-negative results with ELISA kits 4
- Importance of selecting an assay with high sensitivity and specificity for measles surveillance 4