When speaking of the examination phase, where the actual testing of the patient specimens occurs, the term "control" is frequently encountered. What is a control? "Controls are substances that contain an established amount of the substance being tested—the analyte. Controls are tested at the same time and in the same way as patient samples."1
- Controls, which are often purchased from manufacturers, usually use a human base (or closely resemble human serum, plasma, blood, urine, and cerebrospinal fluid) to ensure the analytes being tested parallel human ranges. (These controls are tested as a patient specimen would be tested.)
- Controls have known parameters.
- Some controls are "built-in" to the kits. (These controls are internal to the test system. Examples might be the QC lines on a waived test device or the built-in controls that are inside a molecular test system cartridge.)
- QC programs usually require the same control sample(s) to be tested every day, or every shift that patient testing is done. Note: The QC requirements are different for each laboratory discipline.
- Manufacturers may pool together many human blood samples to create the large volume needed for a single lot number of control.
1. World Health Organization (WHO). Laboratory Quality Management Handbook. CDC and CLSI; 2011. 225.
