UN3373 (Category B Biological Substance)
Also: UN3373, Category B, Biological Substance Category B
The dangerous-goods classification for an infectious biological substance not in a form causing permanent disability or life-threatening disease in healthy people.
UN3373 requires triple packaging under Packing Instruction 650 and specific marking, and is common for clinical and diagnostic samples.
Whether a given sample is Category B rather than Category A or exempt is a determination, not a lookup. The free infectious substance classifier walks the ADR and IATA cascade in order and shows the clause behind each step.
A frozen sample shipped on dry ice combines UN3373 with UN1845.