Reportable range studies are incorporated into the validation process for an automated cell counter. Results of linearity studies are interpreted into the reportable range for the instrument. Linearity is the ability to produce results, within a certain range, that are directly proportional to the concentration or amount of the analyte in the test sample. Each manufacturer will publish a reportable range for each specific analyzer. The linearity analysis results are the actual reportable range for the specific instrument. Commercial products are available for verification of reportable range. The levels have published expected recovery ranges for each analyte. It is important to verify that the commercial products in use extend to the highest and lowest published linearity limits. Other factors such as matrix effect may impact recovery on some of the parameters. The product's package insert should be used as a reference for these limitations.
Patient samples may be used in lieu of commercial product. The patient sample must have sufficient volume to prepare appropriate dilutions. Linear dilutions are prepared. The analyzer diluent may be used to make the dilutions. The Expected recovery may be calculated with the following formula:
Expected Recovery = (Average Undiluted value) x (Dilution Concentration)
Linearity studies are performed on the directly measured parameters, for example WBC, RBC, Hemoglobin, Hematocrit, and platelet count. Varying concentration levels of each analyte are tested over the analyzer manufacturer stated linearity range. The measured values of each analyte are plotted against the expected recovery values and compared graphically to how the plotted curve conforms to a straight line.