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The page below is a sample from the LabCE course PCR Fundamentals: Focus on Multiplex PCR Assay and the Advantages over Singleplex Assays. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Assay Performance

Results gathered during the development and verification of the assay must be analyzed to determine the performance of the assay. In addition, the performance must be gauged by clinical parameters. Key elements include:
Assay parameters
  • Sensitivity - The percentage of true positives that test positive. Highly sensitive tests should be used when the chance of not detecting a disease or as a test component has "significant" consequences. Many screening tests have extremely high sensitivity and results go on to become confirmatory test.
  • Specificity - The percentage of true negatives that test negative (no false positive results). Specificity indicates the correctness of the test in NOT DETECTING closely related organisms or targets.
Clinical parameters
  • Prevalence - How much of a given disease (or test component) is in the population.
  • True prevalence - The proportion of positive disease state (or test component) results divide by the total tested.
  • Predictive value positive - When the test is positive, the probably that it is a true positive.
  • Predictive value negative - When a test is negative, the probability that it is a true negative.
The table below details a standard 2 X 2 comparison, where assay results are compared to a standard or a specific disease state.
STANDARD (DISEASE STATE)
Positive
Negative
ASSAY
RESULTS
Positive
a
b
a+b
Negative
c
d
c+d
a+c
b+d
N
Calculations to assess assay performance:
  • Sensitivity %: a/(a+c) x 100
  • Specificity %: d/(d+b) x 100
  • Prevalence %: (a+b)/N x 100
  • Predictive value positive %: a/(a+b) x 100
  • Predictive value negative%: d/ (d+c) x 100