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General regulatory and quality information for laboratory, pharmacy and supply staff. It is not medical advice and does not describe how to perform the test.
Short answer
The USP 71 sterility test (USP chapter <71> “Sterility Tests”) is the compendial method FDA names as the principal source for sterility testing procedures and media. A passing result means no growth was detected in the small sample tested. It does not prove that every unit in the lot is sterile.
Definition and scope
FDA’s guidance on sterile drug products produced by aseptic processing states that USP <71> is “the principal source used for sterility testing methods, including information on test procedures and media.” The chapter text itself sits in the paywalled USP-NF, so labs and buyers should work from the current edition rather than from summaries.
The legal hooks sit in the US federal regulations. For drugs, 21 CFR 211.167(a) requires that for each batch of a product purporting to be sterile and/or pyrogen-free, “there shall be appropriate laboratory testing to determine conformance to such requirements.” For biological products, 21 CFR 610.12 requires manufacturers to perform sterility testing of each lot of each product’s final container material or other material. Note the wording in 211.167(a): sterile and pyrogen-free are two requirements, which is why a sterility result never substitutes for an endotoxin or pyrogen result.
How FDA expects the test to be used in practice
- Written procedures. Under 21 CFR 610.12 the procedures must describe the sterility test method to be used. Culture-based methods must specify at minimum the composition of the culture media, growth-promotion test requirements and incubation conditions (time and temperature). Each media lot is tested to verify its growth-promoting properties.
- Controlled laboratory environment. FDA’s guidance says the sterility testing laboratory should use facilities and controls comparable to those used for aseptic filling, and that isolators minimize the chance of a false positive.
- Method validation. The method must be shown not to provide an opportunity for false negatives. If the product inhibits growth, the guidance describes modifications such as increased dilution, additional membrane filter washes or inactivating agents.
- Trained staff and qualified media. Media must be rendered sterile and shown to be growth promoting, and personnel must be qualified and trained.
- Alternative methods. Alternate or rapid methods can be considered once shown to be equivalent to or better than traditional methods such as USP.
What a pass does and does not tell you
This is the point most summaries skip. FDA’s guidance says sterility tests “are limited in their ability to detect contamination because of the small sample size typically used.” Quoting USP, it notes the test plan only enables detection of contamination in a lot in which 10% of the units are contaminated about nine times out of ten. FDA’s worked example: in a 10,000-unit lot with 0.1 percent contamination, testing 20 units gives a 98 percent chance the batch would pass.
So a pass is a release check on a sample, not evidence of the sterility assurance level. See sterility assurance level (SAL) and sterilization validation for how sterility is actually assured by the process.
How a positive result is handled
- FDA calls any positive result a serious CGMP issue to be thoroughly investigated, because of the test’s limited sensitivity.
- When growth is observed, the lot should be considered nonsterile and an investigation conducted.
- An initial positive is invalid only where growth can be unequivocally ascribed to laboratory error.
- If a deviation compromised the integrity of the test, the test should be invalidated immediately without incubation.
- Isolates should be identified to the species level and compared with environmental, personnel and bioburden data.
Sterility test vs pyrogen test, bacterial endotoxin test and USP 161
The related tests answer different questions.
| Item | Question it addresses | Where to read more |
|---|---|---|
| Sterility test (USP <71>) | Whether growth is detected in tested units of a lot labelled sterile (21 CFR 211.167(a), 610.12) | This page |
| Pyrogen / bacterial endotoxin test | The separate “pyrogen-free” requirement named in 21 CFR 211.167(a); FDA expects parenteral products to be nonpyrogenic | LAL endotoxin testing, what is endotoxin |
| USP <161> (device extract limits) | Endotoxin and pyrogen limits for devices, covered on the linked page | non-pyrogenic |
| Sterility assurance level | The probability-based sterility claim for a process; a sterility test cannot confirm it | SAL |
| Container closure integrity testing | Used in place of sterility testing in some stability programs | USP <1207> |
Where it matters for labs, clinics and supply decisions
Documents worth asking a manufacturer or contract laboratory about, each tied to the requirements above:
- The written sterility test method and which pharmacopoeial chapter edition it follows (21 CFR 610.12 requires the method to be described).
- Method suitability or validation data showing inhibitory product effects were addressed.
- Culture media growth-promotion records for each media lot.
- A description of the testing environment, for example isolator or aseptic-comparable controls.
- How out-of-specification results are investigated, including species-level identification of isolates.
- For any non-compendial or rapid method, the equivalence data.
For the wider purchasing context, see sterile vs non-sterile purchasing.
Common misunderstandings
- “A pass proves the lot is sterile.” It does not; see the 98 percent example above.
- “Sterility testing covers pyrogens.” Sterility and pyrogen-free are separate requirements in 21 CFR 211.167(a).
- “A positive can be retested away.” FDA says an initial positive is invalid only when growth is unequivocally ascribed to laboratory error.
- “Media growth in a media fill is the same as USP <71>.” Media fills validate aseptic processing and are a different exercise.
FAQ
What is the USP 71 sterility test?
It is the USP-NF chapter <71> “Sterility Tests,” which FDA identifies as the principal source of sterility testing methods, procedures and media.
Is a USP 71 pass proof of sterility?
No. FDA notes the test is limited by small sample size; its example gives a 98 percent chance of passing a 10,000-unit lot with 0.1 percent contamination when 20 units are tested.
Is the sterility test the same as the bacterial endotoxin or pyrogen test?
No. 21 CFR 211.167(a) treats sterile and pyrogen-free as separate requirements. See the linked endotoxin and non-pyrogenic guides.
What happens when a sterility test is positive?
FDA’s guidance says the lot should be considered nonsterile and investigated; the result is invalid only where laboratory error can be unequivocally shown.
Do biological products need sterility testing too?
Yes. 21 CFR 610.12 requires sterility testing of each lot of each biological product’s final container material or other material.
Sources
- 21 CFR 610.12 Sterility, eCFR, ecfr.gov, checked 2026-11-01.
- 21 CFR 211.167 Special testing requirements, eCFR, ecfr.gov, checked 2026-11-01.
- FDA, Guidance for Industry: Sterile Drug Products Produced by Aseptic Processing, Current Good Manufacturing Practice (nonbinding), section XI Sterility Testing, fda.gov, checked 2026-11-01.
- The current text of USP <71> is published in the USP-NF; consult the current edition for procedures.
