Quality Control, Documentation and Record Keeping
Quality assurance covers the whole laboratory pathway, while quality control (QC) monitors each analytical run. Candidates must understand internal QC (known control materials run with each batch, plotted on Levey-Jennings charts with mean and standard deviation limits) and external quality assessment (proficiency testing against other laboratories). Know the Westgard-style rules conceptually: a single result beyond two standard deviations warns, beyond three standard deviations rejects, and trends or shifts indicate systematic problems. Understand calibration (setting the instrument against a known standard) versus QC (verifying performance).
Traps: confusing calibration with QC; accepting a run because only one control failed when the rule requires rejection; failing to act on a trend before it breaches limits; correcting records rather than amending them. Documentation must be contemporaneous, legible, attributable, original and accurate; errors are corrected by a single line, initialled and dated, never erased or overwritten. Know the purpose of SOPs, audit trails, version control, retention periods and confidentiality of results.
Worked example: A chemistry control results at plus 2.5 standard deviations for two consecutive runs. This is a shift, not random variation. Correct action is to stop reporting, investigate (new reagent lot, calibration drift, deteriorated control material), document the investigation, and repeat QC before releasing results.
Rule of thumb: if in doubt, do not report; investigate, document and repeat.