ISO 15189 traceability: metrological traceability explained
Metrological traceability means that a measurement result can be linked back to a recognised reference through an unbroken chain. Under ISO 15189, your laboratory must be able to demonstrate that chain for the measurements used for patient results. The RvA , the Dutch Accreditation Council, checks this during the assessment. Without traceability, a result is hard to compare with that of another laboratory or with an earlier measurement.
This belongs to the requirements on equipment and measurement results in the requirements per chapter. For measurement uncertainty, which is closely related, see the ISO 17025 page on measurement uncertainty, because the principles are similar in both standards. To start with the context, begin with what ISO 15189 is.
Short answer: traceability is the chain from your measurement back to a recognised reference, with a measurement uncertainty at each link. You show that the chain is unbroken, using calibration certificates, reference materials and comparisons.
What does traceability mean in practice?
Imagine a glucose measurement. Your analyser gives a value. That value is only reliable if the analyser was calibrated with a calibrator, which was made according to a reference, which ultimately belongs to a national or international standard. You must be able to show every link.
That sounds abstract, but it is simply a set of documents that connect to each other. A calibration certificate for the calibrator, a reference material with a known value, and a record of the comparison between two methods.
The chain in an example
The following example is fictional. It shows how a clinical chemistry laboratory can record the chain for one measurement.
| Link | What it is | Evidence | Uncertainty |
|---|---|---|---|
| Reference | Recognised reference material with a known value | Supplier’s certificate | Stated on the certificate |
| Calibrator | Material used to set up the analyser | Certificate with value and traceability | Stated on the certificate |
| Analyser | The device that carries out the patient measurement | Calibration log, maintenance record | Calculated in your measurement uncertainty |
| Quality control | Control material measured daily | Control charts with limits | Used to monitor stability |
| Patient result | The result that goes to the doctor | Record with a reference to the calibration | Shown on the report where needed |
This table is a tool. Your own chain may be longer or shorter, depending on your methods. What matters is that each link has evidence and that the links connect to each other.
How do you record it?
Build the chain for each examination. Start with the final result and work back to the reference.
Choose the examination
Start with one examination that is in the scope. A clinical chemistry examination is a logical choice, because many reference materials exist for it.
Find the calibrator and the reference material
Note which material you use, with the lot number and shelf life. Keep the certificate in the file.
Check the calibration of the analyser
Record when the analyser was calibrated, with which calibrator and with what result. Check that the calibration is within its period.
Link the patient result to the calibration
A result must be linked to the calibration and the quality control that applied to that run. This way you can later trace which measurement was checked with what.
Monitor the chain
Check the chain regularly. A new lot number or a new analyser means a new link that you must record.
What does the assessor ask for?
An assessor often chooses one examination and asks for the whole chain. They want the calibration certificates, the record of the reference materials and the link to a patient result.
They also look at uncertainty. A chain without uncertainty is not complete. Use the outcome of the measurement uncertainty as the basis, and apply it to the clinical context. A measurement can be precise within its uncertainty and still differ in a way that matters clinically.
They also look at comparability. If you take part in proficiency testing, the results show whether your measurement agrees with those of other laboratories.
Common mistakes
Certificate present, link missing. A calibration certificate in a folder is not enough. Record which calibration affected which result.
Expired reference materials. A reference material past its shelf life breaks the chain. Check the dates.
No uncertainty for the chain. The assessor wants to see that you know how reliable the measurement is, not only that it was calibrated.
Chains that differ per analyser. If two analysers for the same test use different calibration routes, you must explain and compare them.
What do you do if a link is missing?
Sometimes a link is missing from the chain. A calibrator whose certificate can no longer be found, or a reference material whose traceability was not recorded. That is a finding, and the solution starts with an inventory.
Begin with the question of whether the measurement is still reliable. Sometimes you can show that the result is correct by comparing with another laboratory or with proficiency testing. That does not replace the chain, but it does provide support. Record the result and start a deviation with a root cause analysis.
Then plan the repair. Replace the calibrator or the reference material with an item of known traceability, and record the transition. This gives the assessor confidence that you have solved the problem, not just covered it up.
Why traceability matters for the patient too
A result that is not traceable cannot be reliably compared with the previous measurement of the same patient. A potassium value of 4.1 in January and 4.4 in June can only be interpreted if you know that both measurements were calibrated in the same way.
This makes traceability a patient safety issue. A doctor comparing two results must be able to trust the laboratory. That is why this requirement is part of the core of the standard, and not a technical detail.
See also critical results for how results reach the doctor, and the requirements per chapter for where traceability sits within the standard.
How do you start?
For each measurement procedure, choose the most important links and make an overview. Start with the tests that matter most for the patient. They are the first to be looked at during the assessment.
Also read the quality manual for where this chain sits within the system, and the audit page for what the assessor typically checks in a day.