Table 1 Measures of diagnostic and analytical performance

Diagnostic/clinical accuracy

The ability of a diagnostic test/assay to correctly identify those with the infection or disease of interest and those without the infection or disease.

 • Sensitivity

The ability of a test to correctly identify those with the infection or disease (i.e. true positives/true positives + false negatives).

 • Specificity

The ability of a test/ assay to correctly identify the absence of the disease (i.e. true negatives/true negatives + false positives).

 • Positive predictive value

The probability that when the test result is positive, the infection/disease is truly present (i.e. true positives/true positives + false positives). Predictive values are influenced by the prevalence of the disease in the population being tested.

 • Negative predictive value

The probability that when the test result is negative, the infection/disease is truly absent (i.e. true negatives/true negatives + false negatives).

Analytical performance

The reliability and accuracy of a test/assay for measuring what it seeks to measure.

 • Linearity

The degree to which the results of a test/assay are directly proportional to the amount of analyte.

 • Limit of detection (LoD)

The lowest amount of an analyte that a test/assay can consistently distinguish from absence of the substance.

 • Lower limit of quantification (LoQ)

The lowest amount of an analyte that a test/assay can consistently quantify.

 • Precision

The degree to which repeated measures of an analyte by a test/assay under the same conditions provide the same results.