Laboratory Quality Control for Clinical Laboratories

Laboratory quality control is the process of monitoring analytical performance to ensure patient results remain accurate, reliable and consistent. Quality control activities help laboratories identify analytical issues, verify system performance and support confidence in reported results.

Laboratory quality control programmes typically include internal quality control (IQC), external quality assessment (EQA), proficiency testing and calibration verification. Together, these activities help laboratories monitor day-to-day performance, benchmark results against peer laboratories and verify analytical performance over time.

Internal quality control (IQC) is performed within the laboratory to monitor routine analytical performance through regular testing of control materials. External quality assessment (EQA) compares laboratory performance with peer laboratories and provides independent benchmarking of results.

The frequency of laboratory quality control depends on the test method, laboratory procedures, risk assessment and regulatory requirements. Quality control may be performed daily, per shift, per batch or according to a laboratory's quality management plan.

The number of quality control levels used depends on assay complexity, regulatory requirements and clinical risk. Many laboratories use at least two control levels representing normal and abnormal concentrations, while additional levels may be required to assess performance across the analytical measurement range. Calibration verification protocols commonly evaluate multiple concentration levels across the reportable range.

A failed quality control result should be investigated before patient results are reported. Laboratories should review QC data, determine whether the issue reflects random or systematic error, investigate potential causes, implement corrective action and confirm that acceptable analytical performance has been restored.

Random error results from unpredictable variation within the testing process and may appear as isolated fluctuations in quality control results. Systematic error creates a consistent bias and may be associated with calibration issues, reagent changes or instrument performance problems.

Calibration verification helps confirm that an assay continues to perform accurately across its analytical measurement range. It can identify instrument or assay issues that may not be detected through routine quality control alone and supports ongoing confidence in calibration integrity.

Levey-Jennings charts provide a graphical method for monitoring quality control results over time, while Westgard multirules help laboratories identify random and systematic error patterns that may indicate out-of-control analytical performance and require investigation.

Quality control helps laboratories identify analytical issues, monitor performance trends and detect potential problems before patient results are released. Strong quality management processes, troubleshooting procedures and analytical performance monitoring contribute to reducing diagnostic risk and supporting patient safety.

Comparing results with peer laboratories can help identify systematic bias, highlight performance issues and support continual quality improvement. Peer comparison is a key benefit of EQA and proficiency testing programmes.

Inspection readiness typically includes documented standard operating procedures (SOPs), quality control records, calibration verification documentation, corrective action records and evidence of ongoing analytical performance monitoring and review.

Independent third-party quality controls provide an objective assessment of analytical performance and may help laboratories identify issues not detected by manufacturer-supplied controls. They support routine performance monitoring, troubleshooting and confidence in patient results.