Table 2.
Commonly encountered examples of analytical controls
| Control type | Purpose |
|---|---|
| QCs | Qualitative QCs typically indicate whether specific aspects of the experimental and/or analytical procedure work in the intended ways, and are often included in the same analytical run used to collect study data. For example, a negative control may be a sample or unit that is known to be negative for the outcome and, hence, should assign a negative measurement in the assay. In contrast, a positive control would be expected to assign a positive result. |
| Quantitative QCs are used to monitor the performance of a quantitative measurement system and ensure that it is performing within acceptable limits. Typically quantitative QC samples are run at two or more concentrations across the range of the assay and interpreted using graphical and statistical techniques, such as Levy-Jennings plots and Westgard rules. QC materials are generally not used for calibration in the same process in which they are used as controls. | |
| In instances where any QC checks fail, certain aspects of the experimental procedure may have to be altered in order to remedy the problem or one or more units associated with the violation may have to be reprocessed until satisfactory checks are achieved. | |
| Comparative/normalisation controls | These can be alternative physical or biochemical parameters measured alongside the analyte of interest usually within the same sample, for the purposes of normalisation and/or correction. For example, in RT-PCR housekeeping genes are usually amplified as well as targets of interest, with the final output expressed as a ratio between the target and the housekeeping gene. |