Control materials are made to match patient samples in physical and chemical characteristics. Control samples are often made with biological material.

Control samples are tested in the same way as patient samples. If the results from testing a control sample are not within the acceptable ranges, we assume there has been a problem in the test procedure, equipment, or the samples themselves. There are many criteria for rejecting a test based on the control samples measurements; these criteria will be detailed further in a later section.

Patient results are not reported until the cause of the problem has been found, the problem resolved, and the controls re-run to verify that everything is working normally.