How to Ship UN3373
Category B Specimens
A step-by-step walkthrough of packaging and shipping UN3373 Biological Substance, Category B specimens correctly — so your packages aren't rejected, delayed, or non-compliant.
If your lab ships blood, urine, stool, or swab specimens for diagnostic testing, those packages almost always fall under UN3373, "Biological Substance, Category B." Getting the packaging wrong means rejected shipments, delays, and regulatory exposure. This guide walks through exactly how to do it right.
The short version: Category B specimens require a three-layer "triple packaging" system, a UN3373 diamond mark, the proper shipping name, and carrier-specific handling. No formal hazmat shipping paper is required, but every other rule is mandatory.
Step 1: Confirm Your Specimen Is Category B
Category B covers biological substances being transported for diagnostic or investigational purposes that are not in a form capable of causing permanent disability or life-threatening disease. Most routine patient specimens — blood, urine, stool, nasal swabs, saliva — are Category B. Substances capable of causing severe disease are Category A (UN2814/UN2900) and follow far stricter rules. If there is any doubt that a specimen could be Category A, stop and consult a qualified hazmat specialist.
Step 2: Build the Triple Packaging
- Primary receptacle: The leak-proof container holding the specimen (blood tube, urine cup, swab vial), sealed and watertight.
- Secondary packaging: A second leak-proof layer enclosing the primary receptacle, with enough absorbent material to soak up the entire liquid contents if the primary leaks. Multiple primaries need cushioning so they don't touch.
- Outer packaging: A rigid box of adequate strength. At least one outer surface must be 100 mm x 100 mm minimum.
Step 3: Mark and Label the Package
- The UN3373 diamond mark (a square-on-point at least 50 mm per side) on the outer box.
- The proper shipping name "Biological Substance, Category B" next to the diamond, in letters at least 6 mm tall.
- Sender and recipient names and addresses.
- A responsible-person name and phone number (required by some carriers).
Step 4: Match the Carrier's Rules
USPS, FedEx, and UPS each have specific service tiers and packaging acceptance rules for Category B. FedEx and UPS require Clinical Pak or approved boxes for some lanes; USPS has its own packaging instruction. Always confirm the lane and service level before tendering the package — the triple-packaging standard is universal, but acceptance details differ by carrier.
Step 5: Document and Track
Keep a record of what shipped, when, and to whom, with the tracking number. Good documentation is what separates a compliant operation from a liability — and it is exactly what your lab's auditors will ask for.
Common mistakes we see: not enough absorbent material, using a flimsy outer box, a UN3373 mark that's too small, and forgetting the proper shipping name text next to the diamond.
Frequently Asked Questions
Do I need a hazmat shipping paper for Category B?
No. Category B biological substances are exempt from the formal dangerous-goods declaration, but the triple packaging, UN3373 marking, and proper shipping name are all still mandatory under 49 CFR 173.199 and IATA Packing Instruction 650.
How much absorbent material is required?
Enough to absorb the entire liquid contents of all primary receptacles in the package. If a primary fails, nothing should escape the secondary layer.
Can I reuse boxes for Category B shipments?
Only if the box still meets strength requirements and all old markings and labels are removed or fully covered. A worn or previously-marked box risks rejection.
Related Services
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