Laboratory Quality Management System 92
Control
types
Built-in
controls
Traditional
controls
8-2: Quality control materials
Qualitative and semiquantitative examinations include tests that utilize a variety of
control materials. These controls may be built-in (on-board or procedural) controls,
traditional controls that mimic patient samples, or stock cultures for use with
microbiological examinations.
Built-in controls are those that are integrated into the
design of a test system such as a test kit device. Usually, the
device is marked with designated areas where coloured
lines, bars or dots should appear to indicate success
or failure of positive and negative controls, and these
controls are performed automatically with each test. The
manufacturer’s product instructions may also refer to
these as procedural controls, on-board controls or
internal controls.
Most built-in controls monitor only a portion of the
examination phase, and they vary from one test to another as to what is being
monitored. For example, built-in controls for some kits may indicate that all the
reagents impregnated into the device are active and working properly, whereas
built-in controls for other kits may only indicate that a sample was added and
solutions fl owed through the device correctly. It is important to carefully read the
instructions provided by the manufacturer to understand what the built-in controls
monitor, and to determine whether additional controls may be needed.
Examples of test kits with built-in controls are rapid tests that detect the
presence of antigens or antibodies, such as those for infectious disease (human
immunodefi ciency virus [HIV], infl uenza, lyme disease, streptococcal infection,
infectious mononucleosis), drugs of abuse, pregnancy or faecal occult blood.
Even though these built-in controls give some degree of confi dence, they do not
monitor for all conditions that could affect test results. It is advisable to periodically
test traditional control materials that mimic patient samples, for added confi dence
in the accuracy and reliability of test results.
In some settings, these built-in controls are referred to as internal
controls.
Traditional control materials are made to mimic patient samples and they are tested
with the patient samples to evaluate the examination component. Positive controls
have known reactivity and negative controls are nonreactive for the analyte being
tested. The controls should have the same composition, or matrix, as patient
samples, including viscosity, turbidity and colour, in order to properly evaluate the
test performance. Control materials are often lyophilized when received, and
need to be carefully reconstituted before use. Some manufacturers may provide