What is limit of detection (LOD)?
OD is defined as the titre level where 95% of all replicates of a sample are determined positive. The LOD level is usually determined by probit analysis, resulting in a number together with a range (95% confidence interval), which should always be specified. Note: Results below LOD are still true positives, but less than 95% of all replicates may be determined positive. Example: Consider a fictive assay with LOD 200 copie/mL. At the expected titer 200 copies/mL 95% of the replicates will be reported positive. At 60copies/mL some 50% of the replicates will be reported positive. At 20 copies/mL maybe 20% of the replicates will be reported positive. The LOD of an assay depends on: – Sample preparation, input and output volumes (concentration factor) – Robustness of the PCR system. The ability to amplify one single copy of prepared DNA target. Note: Clinical material should be used, see above.
