From the Guidelines
Varicella IgM testing is crucial for diagnosing recent varicella-zoster virus infection, particularly in immunocompromised patients or those with unclear clinical presentations, and should be performed within the first week of rash appearance for the most accurate results. The test detects the presence of IgM antibodies, which appear early in the infection and remain detectable for about 2-3 weeks 1. A positive result indicates current or very recent infection, while a negative result suggests either no infection or that the test was performed too early or too late in the disease course.
Key Considerations
- Varicella IgM testing is valuable in immunocompromised patients where clinical diagnosis may be challenging due to atypical presentations 1.
- False positives can occur due to cross-reactivity with other herpes viruses, and false negatives may happen if testing occurs outside the optimal window 1.
- Clinical correlation with symptoms and exposure history remains essential for proper interpretation of results.
Clinical Application
In clinical practice, varicella IgM testing can help guide management decisions, such as the use of antiviral therapy or isolation precautions, particularly in high-risk patients like pregnant women or immunocompromised individuals 1. However, the test should be used in conjunction with clinical judgment and other diagnostic tools to ensure accurate diagnosis and effective management. The most recent and highest quality study supports the use of varicella IgM testing as a valuable tool in the diagnosis of varicella-zoster virus infection 1.
From the Research
Varicella IgM
- Varicella IgM is an immunoglobulin that indicates a recent or current varicella-zoster virus (VZV) infection 2.
- The presence of Varicella IgM can be used to diagnose varicella-zoster virus infection, especially when a skin lesion is not typical or apparent 2.
- The VZV IgM-positive period after the onset of herpes zoster is estimated to be around 3.5 weeks (95% confidence interval 2.8-4.6 weeks) 2.
Diagnosis and Treatment
- A speedy and accurate diagnosis of primary varicella zoster infection is essential to prevent life-threatening sequelae, especially in adults and immunocompromised persons 3.
- Post-exposure prophylaxis (PEP) with varicella zoster immunoglobulins (VZIG) should be administered as soon as possible after exposure to the virus, but always within ten days 4.
- Varicella zoster immune globulin (VARIZIG) is recommended by the CDC for postexposure prophylaxis to prevent or attenuate varicella-zoster virus infection in high-risk individuals, such as immunocompromised people, preterm infants, and pregnant women 5.
High-Risk Individuals
- High-risk individuals, such as immunocompromised people, preterm infants, and pregnant women, are at a higher risk of developing severe or complicated varicella 5.
- Varicella incidence was 4.5% in immunocompromised participants, 7.3% in pregnant women, and 11.5% in infants who received VARIZIG 5.
- Postexposure administration of VARIZIG was associated with low rates of varicella in high-risk participants, regardless of when administered within 10 days postexposure 5.