(a). Sensitivity is the lowest value of analyte in assay buffer that the assay can statistically differentiate from background. It is a calculated value, determined by comparing signal from many replicates of low standard wells and zeros. It is possible for the assay’s sensitivity to be higher than the lowest standard point. Sample values found to be below the assay’s sensitivity should be considered to be too low to detect.
(b). LLD is similar to sensitivity, but determined by testing a native sample. Replicate wells of dilute samples and zeros are compared, and the lowest concentration of sample that can be statistically differentiated from zero is determined. In most cases the LLD is higher than the sensitivity.