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Safe transport of blood samples: UN3373 explained

Published 15 October 2026 · Reviewed against the sources below

Blood and other patient samples that go to a laboratory by road are usually classed as dangerous goods: UN3373, Biological Substance, Category B. That sounds alarming, but the rules are short and practical. Here is what clinics, mobile phlebotomists and couriers need to know.

What UN3373 covers

Infectious substances are split into two categories:

Category A (UN2814 for substances that affect humans) covers material that could cause permanent disability or life-threatening disease if exposure occurs. These consignments are rare outside specialist work and are subject to much stricter rules.
Category B (UN3373) covers infectious substances that don't meet the Category A criteria. Most routine diagnostic samples sent for testing that might contain pathogens fall here.

Specimens with only a minimal likelihood of containing pathogens may be transported as exempt specimens, but they still need suitable packaging. Decide the classification with your laboratory and record it in your procedure.

The packaging: three layers (P650)

For road transport, UN3373 must be packed in line with packing instruction P650 of ADR, the international agreement on carrying dangerous goods by road. The packaging must have at least three components:

Primary receptacle, the sample tube itself. It must be leakproof for liquids, and multiple tubes must be wrapped or separated so they can't touch.
Secondary packaging, which is leakproof, with enough absorbent material between it and the primary receptacle to soak up the entire liquid contents.
Outer packaging with cushioning. Either the secondary or the outer packaging must be rigid.

The primary receptacle or the secondary packaging must also withstand an internal pressure of 95 kPa without leaking. The completed package must be capable of passing a 1.2 m drop test. Most commercial UN3373 kits are made to meet this, so buy from a supplier who can confirm compliance and keep that confirmation on file.

The mark and the words

On the outer packaging, against a contrasting background, you need:

the UN3373 diamond, a square set at 45 degrees with sides of at least 50 mm, a line width of at least 2 mm and characters at least 6 mm high
the words "BIOLOGICAL SUBSTANCE, CATEGORY B" next to the diamond, in letters at least 6 mm high.

At least one surface of the outer packaging must measure at least 100 mm x 100 mm. If you use dry ice, extra marking and venting rules apply.

People and paperwork

Under ADR special provision 319, packages prepared and marked to P650 are exempt from most other ADR requirements. Even so, everyone who packs, carries or receives samples should be trained for their role, and you should be able to show it. A good transport procedure also covers:

an itemised list of contents between the secondary and outer packaging, plus sender and recipient details
temperature control and time limits agreed with the laboratory
chain of custody: who handed over what, when, and in what condition
spill kits in vehicles, what to do if a package is damaged, and incident reporting
vehicle cleaning and segregation from food and other goods.

Posting samples has its own, tighter rules and quantity limits, so check the postal operator's conditions before using the post.

Common failings

Absorbent material missing or too little for the volume
An outer box that is too small, or a diamond printed too small
No record of training for drivers or phlebotomists
No temperature or chain-of-custody record, so the laboratory can't show the sample's integrity

The Wardour Collect pack includes a UN3373 transport procedure, chain-of-custody and temperature logs, a spillage procedure and phlebotomy SOPs, all mapped to CQC requirements. It's a template to adapt, not a substitute for the regulations or your laboratory's requirements.