JC Polyoma Virus DNA, Quantitative, Real-Time PCR, CSF

JC Polyoma Virus DNA, Quantitative, Real-Time PCR, CSF is used for the quantification of JCV DNA. The assay is based on real-time PCR amplification and detection of JCV genomic DNA. The quantifiable reportable range is 50 to 50,000,000 IU/mL (1.70 to 7.70 Log IU/mL) and the LOD of the assay is 10 IU/mL.

The LOD and LOQ are critical elements for interpreting the performance of real-time PCR assays. LOD refers to the lowest concentration of JCV DNA in CSF that the assay can reliably detect with 95% confidence. It indicates the minimum amount of viral DNA that can be detected, even if it cannot be precisely quantified.

LOQ is the lowest concentration of JCV DNA that the assay can accurately quantify in a specimen with an acceptable level of precision and accuracy. This quantity is reported in international units per milliliter (IU/mL). The LOQ is often higher than the LOD. A result may be reported as detected but less than the LOQ (ie, for JCV it would be reported, “Detected <50 IU/mL”).

A “Not Detected” result should not be considered equivalent to absence of infection with JCV, particularly when there is high clinical suspicion. In early-stage PML, the JCV viral load in CSF may be extremely low, resulting in a false-negative PCR result.^1,2

Comparing viral load results across laboratories is not recommended. Significant variability in the following elements may result in discrepancies between laboratories:

• Calibration material may not be standardized to measure the viral load.
• Testing platforms and analytical performance may not be equivalent (including target of amplification; target recovery; amplification efficiency, stability, and analytical performance; Limit of Detection [LOD] and Limit of quantification [LOQ]; and even units of measure across different laboratories and assays).
• Units of measurement and analytical measurement range may not be equivalent.

No, cp/mL is not equivalent to IU/mL. An IU is a carefully developed unit of measurement based on World Health Organization (WHO) international standards. WHO standards allow for assays to use the same calibration material, thus using the same reference to measure a viral load. The 1st WHO International Standard for JC Polyoma Virus (JCV), is intended for the standardization of nucleic acid amplification test (NAAT)-based assays for JCV.

It should be used primarily for the calibration of secondary and/or in-house working standards. The WHO material has been evaluated in a worldwide collaborative study involving 23 laboratories using a range of JCV NAAT-based tests and was subsequently established by the WHO Expert Committee on Biological Standardization (ECBS).³

A "Not Detected" JC Polyoma virus (JCV) PCR result, particularly if clinical suspicion remains high, should be considered in the context of the clinical picture.  The presence of small progressive multifocal leukoencephalopathy (PML) lesions with a negative PCR result may be a consequence of a viral load under the Limit of Detection (LOD) and may require additional testing. All test results must be evaluated within the context of the patient's individual immunological status, treatment history, and overall clinical course. In such cases, clinicians may consider^1,2

• Repeating another collection of CSF for retesting.
• A brain biopsy if clinical and radiological suspicion remains strong