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The lower limit of detection (LLD) is the smallest amount of an analyte that can reliably be detected. In practical terms, LLD is the lowest level of analyte that can be statistically distinguished from the blank. LLD is a function of the variability of the blank and the sensitivity of the assay. The blank is tested 20 times within the same run and the mean and standard deviation are calculated. The LLD is considered to be 3 standard deviations above the mean of the blank. Using this formula the chance of misclassification is 7%. If 2 standard deviations are used the chance of misclassification is 16%. Values below the LLD should be reported as "less than the LLD value" rather than a finite value.
