Stephen Macdonald returns with the second in a series of articles on internal quality control, specifically looking in this issue at process design and the impact of the materials used.
An appropriately designed statistical quality control (SQC) process should “verify the attainment of the intended quality of results”.1 This means measuring the performance when the process is stable, detect when it is becoming unstable, and reduce the risk of reporting patient results when the process is out of control. This a requirement of ISO 15189:2012. Compliance is reliant on the use of an appropriate control material. Irrespective of the discipline in which we work, or the nature of our assays, the control material, and what we need from it, is common to us all in pathology laboratories.
Control material characteristics
Defined as a “device, solution or lyophilised preparation intended to monitor the reliability of a test system”,2 control material is central to all SQC processes. Unfortunately, no control material can control all our assays. Many different control materials may need to be used on the same technology, and the same assays often require different control materials.
Control materials for quantitative assays are often validated by manufacturers and provided to us as users with expected values and associated ranges (assayed controls). While helpful to the medical laboratory, quantitative ranges should be verified locally to reflect precision and performance of the system being tested. The initial ranges reflect the performance across a wide range of device and reagent combinations.
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