Positive measles IgM antibody indicates a recent or current measles infection. IgM typically appears around rash onset, peaks in the first 1–3 weeks, and often declines within about a month. False positives can occur, and recent measles vaccination may also trigger IgM. Confirm with clinical findings, IgG seroconversion or PCR. Notify public health and implement isolation precautions until infection is excluded.

Measles-specific IgM is usually reported qualitatively or by an index. Typical ELISA cut-offs are: index <0.9 negative, 0.9–1.1 equivocal, >1.1 positive. IgM becomes detectable around rash onset, peaks within 1–3 weeks, and may persist 4–8 weeks. Exact numeric thresholds vary by laboratory assay, so clinical correlation and repeat testing or PCR may be needed for confirmation.

IgM and IgG serve different purposes: IgM appears early and indicates recent or acute infection, so it's better for detecting recent exposure; IgG appears later and persists, making it better for assessing past infection or longer-term immunity. Neither antibody test reliably replaces direct viral detection for acute diagnosis, and both can produce false results, so timing and clinical context matter.

Measles IgM antibodies typically become detectable about 3 days after rash onset, peak in the first week, and usually remain positive for roughly 1–2 months. In some individuals IgM can persist up to about 3 months. Prolonged or late IgM positivity may reflect a lingering immune response or false positives; PCR testing for viral RNA can help confirm recent infection.

A negative measles IgM means no detectable acute-phase measles antibody, making recent measles infection unlikely. However, testing too early (IgM often appears a few days after rash), prior vaccination, or immunosuppression can cause false negatives. If clinical suspicion persists, clinicians may repeat serology later, perform measles PCR, or check paired IgG titres to confirm diagnosis and guide management.

The best treatment for measles is supportive care: rest, fluids, fever and pain control (paracetamol/ibuprofen), and monitoring for complications. All children with acute measles should receive vitamin A supplements to reduce complications. Severe or immunocompromised cases may need hospital care and specific interventions. Isolate infected individuals and seek medical attention for breathing difficulty, high fever, or dehydration.