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Knowledge

Quality Control in the Medical Laboratory

An introduction to internal quality control, control materials, monitoring, and investigation of analytical performance.

6 min read Laboratory Quality Assurance #time #concentration
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Learning Objectives

By the end of this resource you should be able to:

- Define internal quality control.
- Identify common components of a QC program.
- Distinguish QC from calibration.
- Explain the purpose of investigating QC failure.
- Recognize why QC acceptance criteria are method-specific.

Quality Control in the Medical Laboratory

Overview

Quality control (QC) is part of the laboratory quality-management system used to monitor examination performance and identify conditions that may affect the reliability of results.

QC is not simply a collection of control values. It is a defined process involving materials, procedures, acceptance criteria, review, documentation, and action.

Internal quality control

Internal QC uses control materials or other defined monitoring procedures to assess whether an analytical process is performing acceptably.

A QC program may specify:

  • Control materials
  • Control levels
  • Frequency of testing
  • Acceptance criteria
  • Statistical monitoring
  • Responsibilities
  • Documentation
  • Corrective action

QC and calibration are different

Calibration establishes or adjusts the relationship between a measurement system's response and assigned values according to the applicable method.

Quality control monitors performance after or during routine operation using defined control procedures.

Both can be necessary, but they answer different questions.

QC results and patient results

QC results provide evidence about analytical performance. If QC indicates an unacceptable condition, the laboratory should follow its approved procedure to determine:

  1. What failed?
  2. Is the problem random, systematic, or otherwise characterized?
  3. Are reagents, equipment, calibration, environmental conditions, and controls acceptable?
  4. Is corrective action required?
  5. Could previously produced patient results be affected?

The exact response must be defined by the laboratory's procedure and method.

Trends and shifts

Repeated QC results can show patterns such as:

  • A shift in the central tendency
  • A trend over time
  • Increased variability
  • An isolated outlier

Formal QC rules and decision limits should be established for the examination procedure rather than improvised for an individual event.

Control materials

Control materials should be appropriate for the examination and handled according to their specifications.

Important considerations can include:

  • Lot identification
  • Storage
  • Reconstitution where applicable
  • Expiry
  • Preparation
  • Assigned or expected values
  • Documentation

Quality indicators and corrective action

QC is only useful when the laboratory responds appropriately to evidence of performance problems.

Corrective-action systems may involve investigation of:

  • Reagent issues
  • Calibration problems
  • Instrument maintenance
  • Environmental conditions
  • Operator technique
  • Control preparation
  • Method changes
  • Lot changes

Key points

  • QC monitors ongoing laboratory examination performance.
  • QC and calibration have different purposes.
  • Acceptance criteria should be predefined.
  • QC failures require investigation according to documented procedures.
  • Patient-result impact should be considered when analytical performance is unacceptable.

References

  • World Health Organization. Laboratory Quality Management System: Handbook.
  • ISO 15189:2022. Medical laboratories — Requirements for quality and competence.
  • Clinical and Laboratory Standards Institute. Statistical Quality Control for Quantitative Measurement Procedures.