Thinking Beyond the Thermometer — Smart Sample Transport for ISO 15189

Ask most laboratories how they control sample transport and the answer is a temperature reading on arrival. Under ISO 15189:2022, that is no longer enough. Clause 7.2.5 treats transport as a controlled pre-examination step: appropriate time and temperature limits, documented packaging, and periodic evaluation of the adequacy of the transport system itself. A single spot check cannot demonstrate any of that.

Why a Spot Temperature Reading Isn't Enough

A thermometer that reads 5 °C on arrival tells you the temperature at one instant. It says nothing about a brief excursion two hours earlier, or how long the sample spent in a warm vehicle before pickup. The events that damage samples happen between checks. Compliance — and sample integrity — depends on what happened across the whole journey, not at its end.

Analyte Stability: Why One Rule Doesn't Fit All

Different analytes fail in different ways, which is why transport rules have to be analyte-specific. A few well-documented examples make the point:

Glucose — the glycolysis problem

In an uncentrifuged tube, blood cells keep consuming glucose. Concentrations fall measurably per hour at room temperature unless a glycolysis inhibitor is used or plasma is separated promptly. A transport delay can therefore produce a falsely low glucose.

Potassium — the refrigeration paradox

Counter-intuitively, chilling whole blood can raise measured potassium: cold inhibits the cellular pump that keeps potassium inside red cells, so it leaks out. “Keep everything cold” is the wrong rule for potassium — the right transport condition is analyte-dependent.

Coagulation (APTT) — a narrow window

Some coagulation parameters, APTT in particular, have short stability windows and must reach the analyser within a few hours. A delay that would be harmless for one test invalidates another.

These behaviours are well established in CLSI handling and transport guidance; the practical consequence is that a laboratory must define and monitor time-and-temperature windows per analyte, not apply one blanket rule.

What ISO 15189:2022 Actually Requires of Transport

• Appropriate conditions (7.2.5): time and temperature limits suited to the examinations requested, with packaging instructions.
• Adequacy evaluation (7.2.5): periodic checks that the transport arrangements actually keep samples within those limits — which implies the ability to detect and respond to excursions.
• Traceable receipt (7.2.6): recorded arrival time, condition and handler identity, with defined acceptance/rejection criteria.

Related requirements for collection and transport are set out in ISO 20658; our ISO 20658 explainer covers them.

From Spot Checks to Continuous Monitoring

Meeting these requirements means moving from a single reading to a continuous, documented record. In practice that looks like:

• Time- and temperature-logging along the whole route, tied to the sample's unique identity.
• Automatic alerts when an analyte-specific window is breached, so action can be taken before the sample is compromised.
• A complete chain of custody — who held the sample, when, and under what conditions — from collection to receipt.
• Excursion handling: a documented decision to accept, reject or re-collect, with the reasoning recorded.

This is the “beyond the thermometer” model: transport data becomes evidence, not guesswork. It is also exactly the kind of record that turns an accreditation struggle into a routine export, and it directly reduces the pre-analytical errors that unnoticed excursions cause.

Frequently Asked Questions

What does ISO 15189:2022 say about sample transport?

Clause 7.2.5 requires laboratories to transport samples within time and temperature limits appropriate to the examinations, provide packaging instructions, and periodically evaluate the adequacy of their transport arrangements. Refer to the standard for exact wording.

Why isn't a single temperature check enough?

Because damage occurs between checks. A reading on arrival cannot reveal an earlier excursion or a pre-pickup delay. Demonstrating adequacy requires monitoring across the whole journey and the ability to detect excursions.

Why shouldn't all samples just be refrigerated?

Because refrigeration harms some analytes. Chilling whole blood, for example, causes potassium to leak from red cells and read falsely high. The correct condition is analyte-specific, which is why per-analyte time and temperature windows are needed.

How long can a sample sit before it is compromised?

It depends entirely on the analyte. Some tolerate many hours at room temperature; others, such as certain coagulation tests, have windows of only a few hours. Define windows per analyte and monitor against them rather than applying one rule.

See how S4DX monitors sample transport end to end or request a demo.