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Accuracy

Accuracy Reference range Analytical sensitivity Analytical specificity" Other*

Accuracy Reference range Analytical sensitivity Analytical interferences

┬░CLIA defines analytical specificity as "analytical specificity, including interfering substances." fcCLIA defines this parameter as "any other performance characteristic required for test performance."

┬░CLIA defines analytical specificity as "analytical specificity, including interfering substances." fcCLIA defines this parameter as "any other performance characteristic required for test performance."

When multiple specimen types are to be tested by the assay, the performance characteristics of the assay for each specimen type must be verified. An example is an assay that is designed to detect the presence of cytomegalovirus (CMV). Cytomegalovirus can be detected in whole blood, cerebrospinal fluid (CSF), and amniotic fluid by molecular methods (15). If the assay is to be used by the laboratory to detect CMV in any of these three specimen types, the reference range must be determined for each specimen type independently. This requirement for verification of all specimen types to be used in an assay is applicable for all other performance parameters to be verified. 4. ANALYTICAL SENSITIVITY

Analytical sensitivity refers to the lowest measurable amount of a target nucleic acid that can be detected (qualitative tests), quantified (quantitative tests), or characterized (analytical tests) reproducibly by the assay. The term "detection limit" is often used interchangeably with "analytical sensitivity." The measurement used to define the analytical sensitivity of a test will depend on the type of assay. For assays designed to detect or quantify a particular infectious pathogen in a specimen, the units of measure might be "copies/mL," "colony-forming units/mL," or "plaque-forming units/mL." For assays designed to detect a specific genetic mutation, the analytical sensitivity might be expressed as a percentage. The analytical sensitivity can be reported as 0.1% if the assay can detect one mutant allele in the presence of 999 wild-type alleles.

In each case, analytical sensitivity can be determined by testing specimens with known quantities of the nucleic acid analyte being assayed. Clinical specimens containing quantified target analyte (or a "normal" specimen spiked with a known quantity of the analyte) are serially diluted with normal specimens, or specimen matrix, and assayed to determine the detection limit of the assay. Multiples of each dilution series should be assayed to define the amount or percentage of target analyte that can be detected with 100% confidence. Laboratorians should remember that the analytical sensitivity of an assay refers to the sensitivity of the whole assay, not just the amplification and detection part of the assay. The complete assay procedure, including specimen preparation, must be performed to accurately define analytical sensitivity. For assays in which multiple specimen types can be assayed, the analytical sensitivity must be defined for each specimen matrix to be used in that assay.

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