The dilution series should be made

The dilution series should be made so that at least three dilutions yield hit rates within the range of 0.10 to 0.90 and at least one dilution yields a hit rate exceeding 0.95. It is not desirable to have more than one dilution at either extreme (ie, < 0.10 and/or > 0.95), as this could unduly impact the quality of the probit model fit and resulting LoD estimate. This may require preliminary testing with a single sample to judge the dilution ratios and the number of dilutions to be made. One useful approach is to target dilutions as a geometric series about an assumed LoD level. It is assumed that the diluent used to prepare the dilution series has been shown to provide acceptable linearity over the measurand concentration range tested and that such dilutions are commutable with native patient samples. Increasing the number of dilutions beyond the required five minimum may be useful to improve the quality of the model (eg, eight dilutions with five having hit rates falling in the range of 0.10–0.90 and three with hit rates falling in the range of 0.80–0.99).