Control laboratory
Introduction
Quality control in the laboratory is a mechanism designed to detect, reduce, and correct possible internal analytical deficiencies, before issuing a result. It is intended to increase the quality and reliability of the reported results.
Quality control is basically a measure of precision, or how well a measurement system reproduces the same result over time under different operating conditions.
To do this, use is made of a "control material" on which a series of determinations are made at the beginning of each analytical run, after an instrument receives technical service, every time a batch of reagents is changed, after each calibration, and whenever a result seems inappropriate.[1].
The control material should reproduce, as closely as possible, the same matrix as the samples analyzed, taking into consideration properties such as viscosity, turbidity, composition and color. It should be simple to use, and should have minimal variation between vials since excessive variability can be misinterpreted as random error in the method or instrument. It must be stable over time and must be available in quantities large enough for a single batch to last at least a year. Liquid controls are more convenient than lyophilized ones because variations due to pipetting errors during reconstitution are minimized.
Interpretation
Interpretation of quality control data involves both graphical and statistical methods. Being much more easily interpretable visually, using, for example, Levey-Jennings graphs. In these graphs, the result data obtained when analyzing the control material are recorded on the Y axis, while the X axis indicates the number of the control run; A series of lines representing the mean of the measurement and limits for one, two or three standard deviations are also plotted on the Y axis. By inspecting the pattern of plotted points, a simple way is obtained to detect increases in the associated random error, and displacements or trends associable to systematic errors in the calibrations.[2].
Purpose of Statistical Quality Control
Statistical quality control procedures are designed to monitor the uncertainty of a measurement procedure and alert analysts to problems that could limit the usefulness of a test result for its intended medical purposes. The level of quality required for a clinical laboratory test is based on the medical application. The laboratory must design quality control systems that verify that the desired quality of the results was achieved. The requirement for clinical quality can be established based on the actual performance of a method through the selection of quality objectives.