QC testing is performed within a laboratory to monitor and ensure the reliability of test results produced by the laboratory. Control materials (usually liquid controls) are used to monitor the test system and verify that quality patient test results have been attained. A control is a stabilized sample with a predetermined range of result values that simulates a patient sample.
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 retested to verify that everything is working normally.
