The objective in determining reportable range is to define the highest value that can be reported without diluting the sample. This is usually done by performing a linearity type of experiment, but there is no strict requirement that the method response has to be linear. However, the readout from instrument systems often is linear in the units that are reported. No, for most tests it is sufficient to validate the reportable range using a linearity type of experiment. A more exact estimate of analytical performance around zero is needed only when there is special significance attached to low values for the test.
Drug tests are an obvious example.
Tumor markers are another example. Good planning would be to analyze the number of materials that will be used in routine quality control for that test. In US laboratories, CLIA places certain requirements on the number of materials to be used for different tests - e.g., a minimum of 2 levels or materials. Laboratory practices commonly include 3 materials for certain tests, such as blood gases and hematology. When possible, select control materials that can be continued for QC once the test is implemented in your laboratory.