From the Guidelines
The false negative rate for blood VZV PCR testing can be significant, and a negative test result does not exclude the diagnosis of varicella encephalitis, as stated in the management of encephalitis guidelines by the Infectious Diseases Society of America 1.
Key Considerations
- The sensitivity of blood VZV PCR varies depending on several factors, including the timing of sample collection and the presence of PCR inhibitors in the sample.
- A negative CSF varicella zoster virus PCR result does not exclude the diagnosis, as CSF varicella zoster virus IgM antibodies may still be present 1.
- The utility of PCR assays for the diagnosis of viral infections, including varicella zoster virus, has been demonstrated, but false-negative results can occur.
Diagnostic Approach
- For suspected VZV infections, particularly in immunocompromised patients, it's essential to consider combining blood PCR with direct vesicle fluid sampling for PCR testing, which has a higher sensitivity.
- If clinical suspicion for VZV infection remains high despite a negative blood PCR result, treatment should not be delayed, and additional diagnostic approaches such as direct vesicle testing or serological testing should be considered.
Limitations of Blood VZV PCR
- The false negative rate for blood VZV PCR testing can be substantial, and clinicians should be aware of the limitations of this diagnostic tool.
- Factors affecting false negative rates include low viral load, improper sample collection or handling, PCR inhibitors in the sample, and variations in test methodology between laboratories 1.
From the Research
BLOOD VZV PCR False Negative Rate
- There is limited information available on the false negative rate of BLOOD VZV PCR in the provided studies 2, 3, 4, 5, 6.
- The studies primarily focus on the diagnosis and treatment of varicella-zoster virus (VZV) infections, antiviral resistance, and the detection of VZV antibodies.
- One study discusses the prognostic value of VZV PCR in cerebrospinal fluid in neurological manifestations of varicella, but it does not provide information on the false negative rate of BLOOD VZV PCR 5.
- Another study mentions the emergence of VZV resistance to acyclovir, but it does not address the false negative rate of BLOOD VZV PCR 6.
- Overall, there is a lack of direct evidence on the false negative rate of BLOOD VZV PCR in the provided studies.