Blog · Medical Logistics
UN3373 Explained: How Biological Samples Must Be Packed and Transported
A blood tube travelling from a clinic to a laboratory is not ordinary cargo. It is a regulated dangerous good, and the rules covering it are precise, internationally harmonised, and routinely misapplied.
If your organisation sends specimens anywhere — between clinics, to a reference lab, across emirates, or abroad — someone needs to understand this properly. This is that overview.
Step one: classify correctly
Getting the classification wrong is the actual risk. Everything else follows from it.
Category B — UN3373. Most diagnostic and clinical specimens fall here. The proper shipping name is "Biological Substance, Category B." It covers human and animal material transported for diagnosis or investigation — blood and its components, excreta, tissues and other fluids — where the material does not meet the criteria for Category A.
Category A — UN2814 or UN2900. A materially stricter regime, applying where the source is known to have a serious disease that is readily transmissible and for which effective treatment and preventive measures are not usually available. Different packaging, different documentation, different training.
Exempt material. Some specimens fall outside the dangerous goods rules altogether. But "I assumed it was exempt" is not a defence, and the assessment should be documented rather than assumed.
The rest of this article deals with Category B, UN3373.
Step two: pack to P650
UN3373 is packed under Packing Instruction 650 — written as P650 for road under ADR, and PI 650 for air under the IATA Dangerous Goods Regulations. The requirements are broadly the same across road, air and sea, with minor variations.
The core of it is a triple packaging system.
1. Primary receptacle
The tube, vial or container in direct contact with the specimen.
- Must be leak-proof for liquids, siftproof for solids
- Where multiple fragile primary receptacles go into one secondary package, they must be individually wrapped or separated so they cannot contact each other
- Under IATA, a primary receptacle for liquids must not exceed 1 litre
2. Secondary packaging
Encloses and protects the primary receptacle.
- Also leak-proof or siftproof
- Must contain absorbent material sufficient to absorb the entire contents of the primary receptacle or receptacles if they leak
- Must cushion the primary receptacle against breakage
The absorbent requirement is the one most often under-specified. It is not a token pad — it must be enough to absorb everything.
3. Outer packaging
- Rigid, with at least one surface measuring a minimum of 100 mm × 100 mm
- Under IATA, the complete package must not exceed 4 litres
The 100 mm minimum exists so the required markings physically fit and remain legible.
Performance requirements
The completed package must be capable of passing:
- A 1.2 metre drop test
- An internal pressure of 95 kPa without leakage, across a temperature range of −40°C to +55°C, applied to either the primary receptacle or the secondary packaging
The 95 kPa requirement exists because of air transport. Cargo holds are pressurised to an altitude equivalent well above sea level, and a tube sealed at ground pressure will try to vent. The test ensures the containment survives it.
Step three: mark and label correctly
The outer packaging must display:
- The UN3373 diamond mark — a square-on-point with lines at least 2 mm thick, with the text "UN 3373" in characters at least 6 mm high
- Adjacent to it, the words "BIOLOGICAL SUBSTANCE, CATEGORY B"
- The name and address of the sender and the consignee
- The name and telephone number of a responsible person
- Orientation arrows for liquids in air transport
For overpacks, mark the outside with the word "OVERPACK" and repeat all the required markings.
Carrier-specific requirements exist on top of this. Some carriers require pre-approval or a special commodities agreement for international shipments, and some prohibit Category B outright — in which case the material must be consigned as Category A. Confirm carrier acceptance before booking rather than at the counter.
Temperature control and refrigerants
You can maintain a cold chain and stay compliant, provided the triple packaging remains intact and its performance is not compromised. The rules are specific:
- The primary receptacle and secondary packaging must maintain integrity and performance at the temperature of the refrigerant used, and at the temperatures and pressures that would result if refrigeration were lost
- Ice or dry ice must be placed outside the secondary packaging — inside the outer packaging or in an overpack
- The secondary packaging must be supported internally so it stays in its original position as ice melts or dry ice sublimates
- If liquids are involved, there must still be sufficient absorbent inside the secondary
- Markings on the outer must remain visible
Dry ice brings its own regulation. It is UN1845, requires the package to be vented so pressure cannot build, and carries additional marking including net weight and a Class 9 label. Liquid nitrogen has its own requirements again.
A common and serious error is placing the refrigerant inside the secondary packaging. It defeats the containment design and can compromise the absorbent.
Training is a requirement, not a nicety
Anyone who classifies, packs, marks or offers UN3373 consignments must be trained and competent for their role and for the transport mode used — IATA for air, ADR for road, IMDG for sea. Training must be documented and refreshed, and carriers may ask for evidence before accepting shipments.
This applies to clinic staff who pack the box, not only to the courier. In practice, packing is often done by whoever is nearest the fridge, and that is where most non-compliance originates.
What good specimen logistics looks like beyond compliance
Regulatory compliance keeps the material contained. It does not, on its own, keep the sample usable. A specimen that arrives leak-free but degraded is still a failed shipment, and the patient still needs a repeat draw.
For clinical and research work, look also for:
Temperature monitoring. Continuous logging for the whole journey, not a reading at each end, with a documented excursion procedure. If nobody can tell you what happened in the middle of the journey, the cold chain is not verified.
Chain of custody. A documented record of who held the sample, when, and for how long. Essential for anything with medico-legal weight, and increasingly expected for IVF, cord blood and clinical trial material.
Defined transit times. Many assays have stability windows measured in hours. Transport should be planned against the analyte's requirement, not the courier's convenience.
Trained handlers, not general parcel couriers. Specimen transport is a clinical logistics function. Someone should know what they are carrying, why it matters, and what to do if the vehicle breaks down.
Contingency. What happens if the vehicle is delayed, if the receiving laboratory is closed, or if a package is compromised in transit.
Quick self-check
Run this against your current process:
- Who classified the material, and is the reasoning written down?
- Is the absorbent sufficient to absorb the entire primary contents?
- Does your outer packaging have a face of at least 100 × 100 mm?
- Is the UN3373 mark correctly sized, and is the full text present alongside it?
- Is a responsible person's name and phone number on the package?
- Is refrigerant outside the secondary packaging?
- Is the secondary supported so it does not shift as ice melts?
- Are the people packing your samples trained, and is that training documented?
- Have you confirmed your carrier accepts the shipment on this route?
- Can you produce a temperature record for the whole journey?
Any "no" on that list is worth resolving before it appears in an audit or, worse, in an incident report.
Where ART fits
ART Ambulance Services LLC operates medical sample transportation across all seven emirates for hospitals, laboratories, IVF clinics and cord blood banks — UN3373-compliant packaging, temperature-monitored transit, and documented chain of custody.
We are a DCAS-licensed pre-hospital operator (Permit E24005) and the UAE subsidiary of Ambuce Rescue Team, founded in Belgium in 1975. Specimen transport sits alongside our patient transport work because it draws on the same things: trained people, controlled vehicles, and documentation that holds up afterwards.
+971 800 1020 · info@art-ambulance.ae
This article is for general information and does not replace the current IATA Dangerous Goods Regulations, ADR, or formal dangerous goods training. Requirements change annually — always work from the current edition and confirm carrier-specific rules before shipping.