Quality Control in Respiratory Labs: What Westgard Methods Are and How Rezibase Builds Them Into Your Workflow
Westgard rules are a set of statistical quality control criteria used in clinical laboratories to determine whether a measurement process is in control or whether results should be rejected due to error. In respiratory labs specifically, applying Westgard rules to spirometry quality control is one of the most reliable ways to catch instrument drift, calibration failures, and systematic bias before they affect patient results. Rezibase embeds this framework directly into its accreditation module, meaning labs do not have to manage QC processes manually or across disconnected spreadsheets.
TL;DR
Westgard rules are statistical criteria that flag when lab measurements fall outside acceptable limits of precision and accuracy.
Spirometry quality control depends on consistent, structured QC monitoring to meet TSANZ, NATA, and ISO 15189 standards.
Manual QC tracking in spreadsheets is error-prone and difficult to audit; purpose-built systems reduce this risk.
Rezibase integrates Westgard-based QC directly into the lab workflow, supporting accreditation requirements without added administrative burden.
Labs can centralise documents, training, non-conformances, and QC data in one cloud-based platform.
About the Author: This article was written by the Rezibase team, respiratory scientists and health technology specialists with over 37 years of combined experience building and supporting clinical respiratory and sleep reporting solutions across Australia, New Zealand, the UK, and Ireland.
What Are Westgard Rules, Explained Simply?
Westgard rules are a framework of statistical decision criteria developed to evaluate whether a quality control measurement is acceptable or indicates a problem with analytical performance. Each rule defines a specific pattern in QC data that suggests either random error or systematic error in the measurement process.
The core rules most commonly applied in clinical labs include:
Rule | What It Detects |
|---|---|
1:2s | Warning rule: one QC result exceeds 2 standard deviations |
1:3s | Rejection rule: one QC result exceeds 3 standard deviations (random error) |
2:2s | Rejection rule: two consecutive results exceed 2 SD in the same direction (systematic error) |
R:4s | Rejection rule: one result exceeds +2 SD and another exceeds -2 SD in the same run |
4:1s | Rejection rule: four consecutive results exceed 1 SD in the same direction |
10:x | Rejection rule: ten consecutive results fall on one side of the mean |
The power of using multiple Westgard rules together is that they catch different types of errors. A single rule applied in isolation will miss patterns that a multi-rule approach would catch early.
Why Does Spirometry Quality Control Matter More Than People Assume?
Spirometry quality control is often treated as a compliance checkbox rather than a genuine patient safety tool. That framing undersells its importance.
Spirometry measurements like FEV1 and FVC are used to diagnose obstructive and restrictive lung diseases, monitor disease progression, and guide treatment decisions. If a spirometer drifts by even a small margin due to a calibration issue, and that drift goes undetected, patients may be misclassified, incorrectly cleared for surgery, or have their deterioration missed entirely.
The key risks that structured QC processes are designed to catch include:
Instrument calibration drift over time, particularly in high-volume labs with daily use
Environmental changes such as temperature and humidity affecting sensor accuracy
Consumable or sensor degradation that is not visually obvious
User technique variability introducing systematic bias
Without a defined QC process using Westgard rules, these errors can accumulate silently across hundreds of patient tests before anyone notices.
How Do Westgard Rules Apply Specifically to Respiratory Labs?
The direct application of Westgard rules in respiratory and pulmonary function labs involves running biological QC material or performing calibration verification at regular intervals, then plotting those results against control limits derived from the mean and standard deviation of your expected values.
In practice, a respiratory lab applying Westgard rules would:
Establish control limits based on repeated measurements of a stable QC material (typically a calibration syringe with known volume, or a biological control subject).
Record QC results at defined intervals, often at the start of each session or daily.
Apply the multi-rule framework to each new data point, checking it against the 1:3s, 2:2s, R:4s, 4:1s, and 10:x rules simultaneously.
Flag or reject a run when any rejection rule is triggered, and investigate the cause before reporting patient results.
Document the event, the investigation, and any corrective action taken.
The documentation step is where many labs struggle. Completing the statistical analysis is one thing; creating an auditable trail that satisfies ISO 15189 requirements is another. This is the gap that software-embedded QC is designed to close.
What Do Accreditation Standards Actually Require for QC?
Meeting TSANZ and NATA accreditation standards in Australia, or equivalent standards in the UK and New Zealand, requires laboratories to demonstrate that their quality control processes are systematic, documented, and reviewed regularly.
ISO 15189, the international standard for medical laboratory quality and competence, specifically requires that laboratories:
Define QC procedures and acceptance criteria
Monitor QC data for trends and shifts over time
Document non-conformances and corrective actions
Maintain training records that demonstrate staff competency in QC procedures
Conduct internal audits against these processes
Managing these requirements across separate spreadsheets, paper forms, and email threads is technically possible but creates audit risk. When everything lives in different places, it is hard to demonstrate at a single point in time that your QC program is functioning as documented.
How Does Rezibase Build Westgard QC Into the Workflow?
Rezibase's accreditation module is designed specifically to address the documentation and workflow gap in respiratory and sleep lab QC. Rather than treating QC as a separate administrative task, the platform brings it into the same environment where patient reporting happens.
Key capabilities within the Rezibase accreditation module include:
Westgard-based QC tracking built into the platform, not bolted on as an afterthought
Document management for policies, procedures, and QC reference materials
Training records linked to individual staff members and competency requirements
Non-conformance management with structured workflows for investigation and resolution
Action plans to track corrective and preventive actions through to completion
Internal audit tools aligned to TSANZ/NATA and ISO 15189 requirements
Because Rezibase is cloud-based, all of this data is accessible from any location, relevant for multi-site labs or departments where staff rotate between sites. The platform is already trusted by over 35 sites including NHS facilities in the UK and NSW Health in Australia, meaning its QC framework has been validated in real accreditation environments.
Frequently Asked Questions
What are Westgard rules in simple terms?
They are statistical criteria that tell you whether a quality control result is acceptable or signals a problem with your measurement process. Different rules catch different types of errors, random versus systematic.
Do all respiratory labs need to apply Westgard rules?
Any lab seeking TSANZ, NATA, or ISO 15189 accreditation is expected to have a structured QC process. Westgard rules are the most widely accepted framework for meeting that expectation in clinical laboratories.
How often should spirometry QC be performed?
QC should be performed at a minimum at the start of each testing session. High-volume labs or those with older equipment may benefit from mid-session checks as well. Frequency should be defined in your written QC procedure.
Can Westgard QC be managed in a spreadsheet?
It is possible but carries audit risk. Spreadsheets lack automated rule flagging, version control, and integration with non-conformance workflows, making it harder to demonstrate a functioning QC program during accreditation.
What is the difference between calibration and quality control in spirometry?
Calibration verifies that the device measures correctly and adjusts it if needed. Quality control monitors ongoing performance over time to detect when measurements drift outside acceptable limits, even if the last calibration passed.
Does Rezibase support multiple sites under one QC program?
Yes. As a cloud-based platform, Rezibase supports multi-site deployment, allowing departments across different locations to operate within a consistent, centrally managed QC and accreditation framework.
What standards does Rezibase's accreditation module support?
The module is aligned with TSANZ/NATA accreditation standards and ISO 15189 requirements, covering QC, document management, training, non-conformances, action plans, and audits.
About Rezibase
Rezibase is Australia's most advanced cloud-based respiratory and sleep reporting platform, built by respiratory scientists for respiratory scientists. Developed over 37 years of field experience and now supported by Cardiobase, Rezibase is trusted by over 35 sites including the NHS in the UK and NSW Health in Australia. The platform covers the full lab workflow from patient administration and reporting through to accreditation management, offering vendor-neutral data import, integrated Westgard QC tools, and compliance support for TSANZ, NATA, and ISO 15189 standards. Rezibase is available as a transparent, all-inclusive SaaS solution with no lock-in contracts.
If your lab is looking to strengthen its spirometry quality control program or prepare for accreditation, Rezibase is built to make that process manageable. Visit rezibase.com to learn more or start your free 30-day trial.