Biological Substances: Category A, B or Exempt?

Biological substances are classified for shipping by asking one question at a time. Does the material contain, or could it reasonably contain, a pathogen? If it could, would exposure cause permanent disability or life-threatening or fatal disease? The answers place the shipment in Category A (UN2814 or UN2900), Category B (UN3373), the exempt human or animal specimen group, or the group of materials that are not subject to Division 6.2 at all. Genetically modified microorganisms that are not infectious go to a separate entry, UN3245.

This guide explains each biological substance category, walks through a step-by-step decision flow and answers the training-quiz questions people search for most. It covers biological sample shipping, biological specimen shipping and other biological shipments by air and road, following the IATA Dangerous Goods Regulations (DGR) section 3.6.2 for air, 49 CFR 173.134 for US ground and air transport, and the WHO guidance on regulations for the transport of infectious substances. Classification is the responsibility of the biological substance shipper, the person or organization that offers the package for transport. Use the current edition of each rule and your carrier's own requirements before you pack.

Why classification matters

Every later step depends on the classification. The category sets the proper shipping name, the UN number, the packing instruction, the marks and labels, whether a Shipper's Declaration for Dangerous Goods is needed and which carriers and services will accept the package. A sample placed in the wrong category is wrong on every one of those points at once.

Errors run in both directions. Under-classifying a Category A culture as UN3373 puts a high-risk material in packaging that was never tested to the Category A standard. Over-classifying a routine cholesterol sample as UN3373 is less dangerous but adds cost, limits service options and can delay delivery. In biological shipping, the same mistake can repeat across every biological samples shipment from a site until someone checks the rule. Accurate classifying of biological shipments protects handlers, keeps samples moving and gives the receiving laboratory a package it can accept without questions.

Once you have the classification, our guide to packing and documenting UN3373 samples covers the next steps for Category B shipments.

Dangerous goods and infectious substances

Dangerous goods are articles or substances that can pose a risk to health, safety, property or the environment in transport. Biological shipments often contain two kinds: the specimen itself and the refrigerant around it. Dry ice, for example, is Class 9 dangerous goods (UN1845) even when the specimen it cools is not regulated.

Infectious substances are the part of Division 6.2 that matters here. IATA DGR 3.6.2.1.1 and 49 CFR 173.134 define them as substances known or reasonably expected to contain pathogens. Pathogens are microorganisms, including bacteria, viruses, parasites and fungi, and other agents such as prions, that can cause disease in humans or animals.

What is a biological substance?

In everyday use, a biological substance is any material that comes from a living organism: blood, serum, urine, tissue, swabs, cells, cultures, DNA and biological products such as vaccines. In transport regulations, "Biological substance, Category B" is also a proper shipping name, the one assigned to UN3373. That double meaning causes confusion. There is also no shipping name "Biological substance, Category A." People search for biological substance category A, but Category A material ships as "Infectious substance, affecting humans" or "Infectious substance, affecting animals only." A biological substance in the everyday sense may be Category A, Category B, exempt or completely unregulated. Only the classification decides which.

Biological substances examples by type

Biological goods that reach a shipping desk usually fall into one of these groups.

• Patient specimens: material collected directly from humans or animals, such as excreta, secreta, blood and its components, tissue, swabs and body parts, transported for research, diagnosis, investigation, treatment or prevention.

• Cultures: material in which a pathogen has been intentionally propagated. A patient specimen in transport media is still a specimen, not a culture.

• Biological products: products derived from living organisms, such as vaccines, manufactured and distributed under national authority requirements.

• Medical or clinical waste: waste from the medical treatment of humans or animals or from bioresearch.

• Genetically modified microorganisms and organisms: organisms whose genetic material has been altered.

• Non-infectious biological materials: for example DNA, RNA, non-infectious cells and blood or plasma from people not suspected of infectious disease, which 49 CFR 173.134(b)(2) lists as not subject.

How are biological substances classified for shipping?

Biological substances are classified for shipping by testing them against a fixed sequence: first the exceptions that take a material out of the rules, then the Category A criteria, then the minimal-likelihood test for exempt specimens, with everything infectious that remains assigned to Category B. The WHO guidance publishes a simplified version of this flow, and the IATA DGR and 49 CFR use the same definitions with some differences in detail. The order matters because a material that meets an exception never needs a UN number.

Step-by-step classification decision flow

1. Is the material free of pathogens or excepted? Sterile material, material in which pathogens have been neutralized or inactivated, non-pathogenic microorganisms, environmental samples such as food and water that pose no significant infection risk, blood or tissue for transfusion or transplant, dried blood spots and fecal occult blood screening samples are not subject to the infectious substance rules. Check whether a preservative, refrigerant or other content brings in another hazard class.

2. Is it known or reasonably expected to contain a pathogen in a form capable of permanent disability or life-threatening or fatal disease on exposure? If yes, it is Category A. Assign UN2814 if it affects humans, or humans and animals, and UN2900 if it affects animals only. If you are in doubt, IATA requires Category A.

3. Is it a patient specimen with only a minimal likelihood that pathogens are present? If professional judgment supports that, ship it as an exempt human specimen or exempt animal specimen in triple packaging, without a UN number.

4. Is it a genetically modified microorganism or organism that does not meet the infectious or toxic definitions? If yes, classify it as UN3245 under Class 9.

5. Everything else that is infectious is Category B and goes to UN3373, "Biological substance, Category B." Medical or clinical waste follows its own entries (UN3291, or UN2814, UN2900 or UN3549 for Category A waste).

6. Add the refrigerant. If dry ice is used, add UN1845 requirements to the package, whatever the specimen category.

Professional judgment drives steps 2 and 3. IATA and 49 CFR both tie it to the known medical history and symptoms of the source, endemic local conditions and the individual circumstances of the source human or animal. A person who knows why the sample was taken and what it will be tested for should make that call.

Biological substance categories at a glance

The table below pairs each biological substance category with its UN number, proper shipping name and main air packing instruction. It is a quick reference, not a replacement for the regulation text.

The packing instruction numbers in the table are the IATA air references. For the detailed requirements of each, see our IATA biological packaging guide to PI 650, PI 620 and PI 954.

Category A infectious substances

A Category A infectious substance is the highest-risk group. It is assigned to UN2814 when it can cause disease in humans, or in both humans and animals, and to UN2900 when it causes disease only in animals. For solid medical waste from the medical treatment of humans or animals that contains Category A material, IATA and 49 CFR also allow UN3549. The shipping names, and how they differ from UN3373, are explained in our article on the difference between UN 2814, UN 2900 and UN 3373 and in the glossary entry on UN2814 for humans and UN2900 for animals.

What is a Category A biological substance?

A Category A biological substance is an infectious substance transported in a form that, when exposure to it occurs, is capable of causing permanent disability or life-threatening or fatal disease in otherwise healthy humans or animals. That is the wording in IATA DGR 3.6.2.2.2.1 and 49 CFR 173.134(a)(1)(i). An exposure happens when the substance is released outside its protective packaging and comes into physical contact with humans or animals.

So the quiz statement "Category A is an infectious substance transported in a form that, when exposure to it occurs, is capable of causing permanent disability or life-threatening or fatal disease to humans or animals" is true. The regulations add "otherwise healthy," which narrows the test to the general population rather than vulnerable patients.

The Category A infectious substance list

The IATA DGR gives an indicative list of Category A examples in Table 3.6.D, and the WHO guidance reprints the UN Model Regulations list in its Annex 3. The list includes agents such as Ebola virus, Marburg virus, Lassa virus and Variola virus in any form, and many others only as cultures. Hepatitis B virus, human immunodeficiency virus, Mycobacterium tuberculosis and rabies virus, for example, appear with the note "cultures only."

The list is not exhaustive. New or emerging pathogens that meet the criteria must be assigned to Category A even if they are not listed, and IATA states that a substance must be included in Category A when there is doubt. If an unknown agent is suspected to meet the criteria, the WHO guidance says "suspected Category A infectious substance" is added in parentheses after the proper shipping name on the transport document.

Category A vs Category B infectious substances

The difference between Category A vs Category B is the severity of harm on exposure, not whether the material is infectious. Both are infectious substances in Division 6.2. Category A can cause permanent disability or life-threatening or fatal disease in otherwise healthy people or animals. Category B can cause infection but does not meet that threshold. Category A therefore needs tested UN-specification packaging and a Shipper's Declaration, while biological category B material uses PI 650 packaging and no declaration.

Why the same pathogen can be Category A or Category B

Category A depends on the form, not only on the organism. A culture concentrates the pathogen, so a culture of HIV or Mycobacterium tuberculosis is Category A. A blood sample from a patient being tested for HIV is a patient specimen. It is usually Category B, because the organism appears on the indicative list only for cultures. That is why "category a vs b infectious substances" is a question about the material and its purpose, not just the name of the agent.

Category A shipping and packaging

Category A packaging is triple packaging that has passed the UN specification tests and carries the UN packaging mark. Under 49 CFR 173.196 it includes a leakproof primary receptacle, a leakproof secondary packaging, a rigid outer packaging at least 100 mm at its smallest external dimension and an itemized list of contents between the secondary and outer packaging. Category A shipping also needs a Shipper's Declaration for Dangerous Goods for air. The WHO guidance states that a dangerous goods transport document is required for all Category A shipments.

Two limits often appear in training questions. First, the exclusive-use motor vehicle exception in 49 CFR 173.134(b)(10) covers Division 6.2 material "other than a Category A infectious substance." So the statement "Category A substances can be transported by courier under the exclusive motor vehicle exemption" is false. Second, USPS Publication 52 section 346 states that Category A infectious substances are nonmailable.

Category B biological substances

Category B is the group for infectious substances that do not meet the Category A criteria. Most diagnostic specimens from patients with known or suspected infections fall here. A Category B infectious substance is shipped as UN3373 under the proper shipping name "Biological substance, Category B." Older documents may still say "diagnostic specimen" or "clinical specimen," but those are no longer the shipping names.

What is a Category B biological substance?

A Category B biological substance is an infectious substance that does not meet the criteria for Category A. 49 CFR 173.134(a)(1)(ii) describes it as an infectious substance that is not in a form generally capable of causing permanent disability or life-threatening or fatal disease in otherwise healthy humans or animals when exposure to it occurs. It must be described as "Biological substance, Category B" and assigned UN3373.

The quiz statement "A Category B biological substance is an infectious substance not in a form generally capable of causing permanent disability or life-threatening or fatal disease in humans or animals" is therefore true. It matches the US definition almost word for word, without the "otherwise healthy" qualifier.

Biological substance category B examples

• Blood from a patient being tested for HIV or hepatitis B, shipped to a reference laboratory.

• Swabs or serum from a patient with a suspected respiratory infection, such as COVID-19, sent for diagnosis.

• A culture of an organism that is not on the Category A list, such as Staphylococcus, sent for identification or subtyping.

• Animal specimens collected to diagnose a disease that is not a Category A agent.

Category B shipping and packaging

Category B substance shipping uses lighter packaging than Category A. Category B infectious substance packaging follows PI 650 for air and 49 CFR 173.199 in the US. It is triple packaging with absorbent material for liquids, a rigid outer packaging with at least one surface of 100 mm by 100 mm and a UN3373 mark. The completed package must pass a 1.2 meter drop test. For aircraft, 49 CFR 173.199 limits liquids to 1 L per primary receptacle and 4 L per outer packaging, not counting the refrigerant. The packaging manufacturer must provide filling and closing instructions, and the shipper must follow them.

Commercial shipments of Category B specimens must be labeled with which 4-digit UN identification number?

They must be labeled with UN3373. A UN3373 package packed and marked according to PI 650 is not subject to other requirements of the regulations, so it does not need a Shipper's Declaration. Dry ice adds UN1845 marks and air waybill details. Category B shipping by USPS is limited to Priority Mail and Priority Mail Express under USPS Publication 52 section 346.

Can Category A samples be mixed with Category B samples?

No. Category A samples should not be mixed with Category B samples in a UN3373 package, so the training statement "Category A samples can be mixed with Category B samples" is false. 49 CFR 173.199(a)(9) states that a packaging containing Category B inner packagings may not contain other hazardous materials except refrigerants, anticoagulants and small quantities of preservatives. A Category A substance is none of those. PI 650 packaging is also not tested to the Category A standard.

The rule depends on what you are trying to do. If both specimens travel in one outer box, the whole package must be treated as the higher-risk material: UN-specification Category A packaging, Category A marks and labels and a Shipper's Declaration. The sources reviewed for this guide do not set out a separate mixed-category procedure, so most shippers keep the samples in separate packages, each classified on its own. If several packages travel together, they can go in an overpack, which must be marked "OVERPACK" and show the marks of the packages inside unless those are visible.

Can Category A and B be shipped together on one consignment?

Separate, correctly marked packages can usually travel on the same consignment, subject to carrier acceptance. The constraint is the packaging, not the air waybill. Confirm with your carrier, because operator variations to the IATA DGR can restrict Category A acceptance further.

Genetically modified organisms and microorganisms

Genetically modified organisms (GMOs) and genetically modified microorganisms (GMMOs) are organisms whose genetic material has been altered from its natural state. IATA DGR 3.6.2.4 sends GMMOs that do not meet the definition of an infectious substance to Class 9, subsection 3.9. The WHO guidance makes the same point: GMOs and GMMOs that do not meet the definition of toxic or infectious substances must be assigned to UN3245.

What is UN3245?

UN3245 is the UN number for "Genetically modified microorganisms" or "Genetically modified organisms," a Class 9 entry for engineered organisms that do not meet the definition of an infectious or toxic substance. A typical example is a non-pathogenic laboratory strain of E. coli engineered to express a harmless protein. For air, UN3245 is packed under PI 959. Under the UN Model Regulations special provision 219, which corresponds to air special provision A47, a GMMO or GMO packed and marked under P904 (PI 959 for air) is not subject to any other requirements of the regulations.

Genetically modified microorganisms are classified as infectious substances when

Genetically modified microorganisms are classified as infectious substances when they meet the definition of an infectious substance, that is, when they are known or reasonably expected to contain a pathogen able to cause disease in humans or animals. They are then Division 6.2 and go through the normal test. An engineered pathogen that meets the Category A criteria is UN2814 or UN2900. One that does not is UN3373. Only the non-infectious and non-toxic GMMOs stay in UN3245. Some GMO shipments also fall under separate rules, such as national biosafety permits and the Cartagena Protocol, which the WHO guidance mentions.

Exempt human or animal specimens

An exempt human specimen or exempt animal specimen is a patient specimen for which there is minimal likelihood that pathogens are present. IATA DGR 3.6.2.2.3.8 lets it travel without most of the infectious substance rules if it is in triple packaging: a leakproof primary receptacle, a leakproof secondary packaging and an outer packaging with at least one surface of 100 mm by 100 mm, with absorbent material for liquids. The outer package is marked "Exempt human specimen" or "Exempt animal specimen." There is no UN number.

The IATA examples include blood or urine tests to monitor cholesterol, blood glucose, hormone levels or prostate specific antigen, organ function tests for patients with non-infectious diseases, therapeutic drug monitoring, insurance or employment tests for drugs or alcohol, pregnancy tests, biopsies to detect cancer and antibody detection where infection is not a concern. Exempt human specimens and exempt animal specimens are common in clinical research and routine diagnostics. Our guide to shipping exempt human and animal specimens covers packaging and marking in more detail.

How US ground rules differ from IATA

49 CFR does not use the "exempt human specimen" label in the same way. 49 CFR 173.134(b)(11) states that samples for routine testing not related to infectious disease, such as drug or alcohol, cholesterol, glucose, PSA, kidney or liver function or pregnancy tests and cancer biopsies, are not subject to the hazardous materials regulations when there is a low probability the sample is infectious. Air shipments still follow IATA, so a sample flown by an express carrier normally needs the exempt marking and triple packaging even when it would be unregulated by US ground rules. USPS Publication 52 also requires triple packaging and the exempt mark for these specimens in the mail.

Exempt human specimen HS code

"Exempt human specimen" is a transport classification, not a customs code. Human blood falls under HTS heading 3002, while other human or animal materials may classify elsewhere depending on what they are. Our guide to HS codes for healthcare and life sciences explains how to approach the tariff side.

Not subject to Division 6.2

Some biological materials are not subject to Division 6.2 at all. IATA DGR 3.6.2.2.3 and 49 CFR 173.134(b) list, among others, substances that do not contain infectious substances or are unlikely to cause disease, non-pathogenic microorganisms, neutralized or inactivated pathogens, environmental samples that pose no significant risk, dried blood spots, fecal occult blood screening samples and blood or tissues collected for transfusion or transplantation. These materials carry no UN number and no infectious substance mark, unless they meet the criteria of another hazard class.

Being "not subject" is different from being an exempt specimen. Exempt specimens still have mandatory triple packaging and marking under IATA. Materials not subject to the regulations do not. The WHO guidance still recommends basic triple packaging for these excepted materials when they move by air, so leakproof packaging remains good practice.

How would you classify a fecal occult blood card for packaging and shipping purposes?

A fecal occult blood card is classified as not subject to Division 6.2 regulation. IATA DGR 3.6.2.2.3.6 states that fecal occult blood screening samples are not subject to the regulations, and 49 CFR 173.134(b)(9) excepts specimens for fecal occult blood detection placed on absorbent filter paper or other material. So of the usual quiz options (Category A infectious substance, Category B infectious substance, not subject to Division 6.2 regulation, exempt specimen) the best answer is "not subject to Division 6.2 regulation."

The answer depends on the card being a dried screening sample on absorbent material. A liquid stool specimen sent to diagnose an infection is a different material and goes through the full decision flow. The WHO guidance groups fecal occult blood samples with the full exceptions and recommends basic triple packaging when they travel by air, and some carriers or postal services set their own packing rules. Use a sealed envelope or pouch as the program supplies.

Answers to common classification quiz questions

These questions come up in shipper training and are searched often. Each answer gives the regulatory reason and the conditions it depends on.

How should a tissue sample from a healthy individual for human leukocyte antigen (HLA) typing be classified if shipped on dry ice, by air, and via FedEx?

Classify the tissue as an exempt human specimen and add the dry ice requirements for UN1845. HLA typing is an immunological test unrelated to infectious disease, and a healthy donor gives a minimal likelihood that pathogens are present, which meets the IATA DGR 3.6.2.2.3.8 test. The dry ice is still dangerous goods by air. IATA 3.6.2.2.3.8(e) requires all applicable dry ice requirements to be met, so the package needs a design that vents carbon dioxide, the UN1845 and Class 9 marks and labels, the net quantity of dry ice and the dry ice details on the air waybill under PI 954. Confirm FedEx's own dangerous goods acceptance terms for your account. If the tissue were intended for transplant, it would be not subject to the regulations. If the donor were suspected of an infection, it would be Category B.

A blood specimen from a healthy individual is being sent by aircraft from your laboratory to a reference laboratory for a routine cholesterol test. This specimen is classified as what type of substance?

It is an exempt human specimen. Cholesterol testing is one of the named IATA examples, and nothing suggests infection. By air it needs triple packaging and the "Exempt human specimen" mark. Sent only by US ground transport, the same sample would be not subject to 49 CFR under 173.134(b)(11).

A blood specimen for HIV testing is being sent to a reference laboratory within the United States. How should it be classified for packaging and shipping purposes?

It is a Category B specimen, UN3373. The test is for an infectious disease, so the exempt route does not apply. Human immunodeficiency virus is on the Category A indicative list only as cultures, so a patient blood sample is Category B unless professional judgment points to something more serious.

How would you classify a tube containing a pure culture of Staphylococcus spp. being transported for subtyping?

It is normally Category B, UN3373. It is a culture, but Staphylococcus is not on the Category A indicative list, and Category A depends on the agent and form meeting the severe-harm criteria. If the shipper has information that the strain meets those criteria, it must be classified as Category A instead.

A biological specimen from an otherwise healthy patient that must be shipped to a diagnostic laboratory for cancer screening can generally be shipped as a __________.

It can generally be shipped as an exempt human specimen. IATA names biopsies to detect cancer as an example, and 49 CFR 173.134(b)(11) names cancer biopsies for US ground transport.

A packaging requirement for Category A infectious substances, Category B infectious substances, and exempt specimens is:

Triple packaging. All three require a leakproof primary receptacle, a leakproof secondary packaging and an outer packaging. What changes is the standard: UN-specification tested packaging for Category A, PI 650 packaging with a drop test for Category B, and basic triple packaging of adequate strength for exempt specimens.

For which of the following specimens would this form be required?

When the form in the question is the Shipper's Declaration for Dangerous Goods, the answer is Category A. Of the usual options (Category A, Category B, Category B with dry ice, exempt), the declaration is required only for Category A. The WHO guidance states that UN3373 packed under PI 650 does not need a dangerous goods transport document, and dry ice used with Category B is documented on the air waybill. Exempt specimens need none.

A living microorganism or its toxin that may cause human disease that is transported through the U.S. mail must be marked as a(n) __________.

Older training material used the term "etiologic agent." Current USPS Publication 52 section 346 works with the Category A and Category B scheme instead. Category A infectious substances are nonmailable, and mailable infectious substances must be Category B, marked "Biological Substance, Category B" and "UN3373," with the biohazard symbol on the secondary packaging.

Identification: proper shipping name and UN number

Each regulated classification has a proper shipping name and a UN number that appear on the package and, where required, on the shipping documents. Exempt specimens and materials not subject to the rules have neither.

• Category A: UN2814, Infectious substance, affecting humans. UN2900, Infectious substance, affecting animals only. The technical name of the agent goes in parentheses on the declaration, not on the package.

• Category B: UN3373, Biological substance, Category B.

• Genetically modified, non-infectious: UN3245, Genetically modified microorganisms or Genetically modified organisms.

• Medical waste: UN3291 for Category B or low-probability waste, UN3549 for solid Category A medical waste from medical treatment.

• Dry ice: UN1845, Dry ice or Carbon dioxide, solid, with the net quantity marked.

• Exempt specimens: the words "Exempt human specimen" or "Exempt animal specimen," no UN number.

Biological samples shipping containers and dry ice

Biological samples shipping containers follow from the classification. A Category A shipment needs a UN-specification box marked as tested to the Category A standard. A Category B shipment needs a PI 650 or 49 CFR 173.199 system, usually sold as a UN3373 kit with instructions. An exempt specimen needs basic triple packaging of adequate strength. In each case the primary receptacle and secondary packaging must stay intact at the temperature of the refrigerant and if refrigeration is lost.

When dry ice is used, place it outside the secondary packaging or in an overpack, use interior supports so the secondary packaging stays in position as the ice sublimates and never seal it in a gas-tight container. For quantities and venting, see our dry ice shipping instructions. Dry ice changes the category of nothing, but it adds its own rules to everything.

Special cases: HeLa cells, cultures and medical waste

HeLa cells shipping, customs and biological materials regulations

HeLa cells are a human cell line. For transport, non-infectious cells and tissue cultures are listed as not subject in 49 CFR 173.134(b)(2), so an uninfected HeLa culture is generally not regulated as Division 6.2. A culture that has been infected with, or may carry, a pathogen goes through the full classification. For import into the United States, the CDC import permit rule in 42 CFR 71.54 applies to infectious biological agents and infectious substances, and USDA APHIS may require a permit where cell cultures have been exposed to livestock or poultry pathogens, for example through animal-origin media. Our guide to importing human-derived materials into the United States covers the permit and declaration side.

Medical or clinical waste

Medical waste containing Category A material is UN2814, UN2900 or, for solid waste from medical treatment, UN3549. Waste containing Category B material, or with a low probability of containing infectious substances, is UN3291. Decontaminated waste is not subject to the infectious substance rules unless it meets another hazard class.

Practical classification examples

These examples apply the decision flow to common laboratory shipments. Each one assumes the stated purpose and history, so a different history can change the answer.

Final thoughts

Classifying biological shipments comes down to the material, its form and why it is being shipped. Work through the exceptions first, test for Category A with the indicative list and professional judgment, decide whether the specimen is exempt and assign Category B to what remains. Then add the refrigerant. When the history is unclear, IATA and the WHO guidance both point the same way: treat the material as the higher category.

Mercury ships biological specimens, including UN 3373 samples, with IATA-compliant packaging and cold chain support. The classification itself still belongs to the shipper, who knows the source and purpose of each sample.