Sigma Metrics for Assessing Accuracy of Molecular Testing

For any diagnostic testing, the bar for accuracy is high, for good reason. Disease status and therapy decisions are often defined by a single positive or negative result. In the case of molecular viral load testing of patients with hepatitis or human immunodeficiency virus infections, expensive antiviral therapies are continued or terminated based on laboratory results. If these results are not accurate, patients may be subjected to additional testing or to treatments, which can add expense, worry, and in some cases medical harms. Viral load cutoff points for therapeutic decisions have been recently lowered; therefore, test result accuracy near the assay's lower limit of quantitation is even more important today than in the past. How can molecular diagnostic laboratories improve the assessment of their viral load assay's accuracy? Answers can be found in the statistical assessment of results derived from testing quality control material. The statistical tools are collectively called Sigma metrics. This review will detail the aspects of Sigma metrics that relate to viral load testing, and also review recent literature for common viral load testing as it relates to Sigma metrics.