In a medical laboratory environment, even a small error in a temperature reading can have serious consequences — from invalidating diagnostic samples to compromising the efficacy of temperature-sensitive reagents and medicines.
ISO 15189:2022 requires laboratories to establish, apply, and document decision rules that define how results are evaluated against specified limits, including consideration of Measurement Uncertainty (MU).
For laboratories storing samples, blood products, or controlled medicines, this means that pass/fail decisions for temperature compliance must be made in a way that is both technically valid and defensible to regulators such as UKAS.
Measurement uncertainty is the quantified doubt that exists about a measurement result. No measurement is perfectly exact — MU defines the range within which the true value is expected to lie, with a stated level of confidence.
In temperature calibration, MU is expressed in degrees Celsius (°C) and includes all sources of variability, such as:
Clause 7.3.3.2 of ISO 15189 requires that:
Laboratories shall determine the measurement uncertainty for each measurand and factor this into the evaluation of conformity to specification.
In practice, this means:
In the context of laboratory temperature monitoring, there are two common approaches to applying MU in decision rules:
Guard banding reduces the acceptance limit by the MU value, meaning that any reading near the specification limit — even if within tolerance — may be considered a fail if MU pushes it over the limit.
This is the most conservative approach, providing the highest assurance of compliance.
Example: Guard Banding Applied to alarm limits:
In this example, the Sematics platform could be configured so that alarms trigger at +7.76 °C instead of +8.0 °C. This “built-in” guard band ensures that even with MU, no result above the true limit is accepted.
Advantages:
Disadvantages:
JTF Solution:
In Sematics, we can apply MU adjustments across multiple devices simultaneously using group profiles, ensuring decision rules are implemented consistently.
Shared acceptance — sometimes referred to as shared risk — is recognised under ISO 15189 and UKAS LAB 48 as an alternative to full guard banding.
It allows for a mutually agreed level of risk, where results close to the specification limit but within MU can still be accepted. This can reduce unnecessary failures, but must be formally documented and, if required, agreed with the accrediting body.
At JTF Wireless:
Important: The decision to adopt shared acceptance and define acceptable risk is the responsibility of the laboratory, not the calibration provider.
ISO 15189 and UKAS LAB 48 both recognise shared acceptance as a valid approach when documented and agreed in advance. This decision rule allows laboratories to define pass/fail criteria that account for measurement uncertainty without unnecessarily rejecting results that remain safe and compliant.
For more detail on how UKAS approaches decision rules and measurement uncertainty, see the official guidance:
UKAS LAB 48: Decision Rules and Statements of Conformity.
With JTF Wireless and Sematics, you gain a fully integrated approach to MU and decision rule application:
Measurement uncertainty is not just a regulatory requirement — it’s a critical part of ensuring your laboratory’s temperature monitoring is both accurate and defensible.
By understanding MU and applying decision rules such as guard banding or shared acceptance, laboratories can meet ISO 15189 obligations while maintaining operational efficiency.
With Sematics and JTF Wireless, you can:
Whether you choose full guard banding or shared acceptance, our goal is the same — to help you protect your results, your compliance, and your reputation.
UKAS LAB 48: Decision Rules and Statements of Conformity
United Kingdom Accreditation Service (UKAS)
Official UKAS guidance on applying decision rules and factoring measurement uncertainty into conformity statements.
Read UKAS LAB 48 on the UKAS website
ILAC G8: Guidelines on Decision Rules and Statements of Conformity
International Laboratory Accreditation Cooperation (ILAC)
Explains how decision rules are applied internationally when determining compliance with a specification, especially when measurement uncertainty is considered.
Download ILAC G8 from the ILAC website
UKAS M3003: The Expression of Uncertainty and Confidence in Measurement
United Kingdom Accreditation Service (UKAS)
Details the methodology for evaluating and expressing measurement uncertainty, widely referenced by UKAS-accredited laboratories.
View UKAS M3003 from the UKAS website
EA-4/02: Evaluation of the Uncertainty of Measurement in Calibration
European co-operation for Accreditation (EA)
Provides guidance on evaluating measurement uncertainty in calibration
Read EA-4/02 on the EA website
