Sterility testing for peptides: USP <71> vs PCR screens vs microbial counts

What a sterility test answers

A sterility test asks whether live bacteria or fungi grow from the units tested. The reference method is USP <71> Sterility Tests, which FDA guidance names as the principal source of sterility test methods for sterile drug products. It is harmonised with the European Pharmacopoeia (2.6.1) and the Japanese Pharmacopoeia (4.06), and ICH recommends the three texts as interchangeable. If nothing grows in two culture media over at least 14 days, the units comply.

The harmonised text is plain about the limit: a satisfactory result shows only that no contaminating organism was found in the sample examined, under the conditions of the test. EU rules for sterile manufacture call the finished-product test “the last in a series of critical control measures”.

Research peptides carry no sterility specification, so a test is the buyer’s choice and describes only the vials sent. Endotoxin needs its own test: see endotoxin vs sterility.

The USP 71 sterility test procedure

A freeze-dried peptide that dissolves is tested as a soluble solid, in a sterile solvent such as water for injection or saline. Membrane filtration, used whenever the product allows it, passes the solution through a filter with a nominal pore size of 0.45 µm or less, and the filter goes into the media. Direct inoculation puts the product straight into the medium, at no more than 10% of its volume.

Step	What the chapter sets	Why
Two media	Fluid thioglycollate medium at 30–35 °C, mainly for anaerobic bacteria; soya-bean casein digest medium at 20–25 °C, for fungi and aerobic bacteria	Covers organisms that need air and organisms that grow without it
Media checks	Each batch stays clear for 14 days, and shows clear growth from no more than 100 colony-forming units (CFU) of each of six reference organisms: three aerobic bacteria, one anaerobe and two fungi	Shows the media are clean and can support growth
Method suitability	The test run with the product plus no more than 100 CFU of each organism	Shows the sample does not hold back growth and hide contamination
Incubation	Not less than 14 days, with the media examined at intervals	Any earlier reading is preliminary
Cloudy samples	Portions moved to fresh medium at day 14 for at least 4 more days	Tells product haze apart from growth
Negative controls	Run with each test	Shows growth did not come from the test itself

Growth means the units do not comply, unless the lab shows the test was invalid for a listed reason, such as growth in the negative controls or a fault in the procedure. A repeat uses the same number of units.

USP 71 sterility testing sample size: how many vials

The chapter sets a minimum number of containers per batch. For injectable products:

Containers in the batch	Minimum tested, per medium
Up to 100	10% or 4, whichever is greater
101 to 500	10
More than 500	2% or 20, whichever is less
Not known	The maximum, which is 20

For solids under 50 mg per container, the test uses the whole contents of each container, so a 5 mg or 10 mg peptide vial is used in full. US pharmacies that compound sterile preparations follow USP <797>, which lets a batch of 1 to 39 units be tested on 10% of the units, rounded up.

Peptide labs ask for anything from one dedicated vial to 20. TrustPointe, citing the USP table, asks for 4 to 20 unopened vials and pools them. Our guide on how many vials to send lists each lab’s request.

What a passing result can and cannot show

The sample is small, so the test misses most low-level contamination. FDA guidance gives numbers: the standard sampling plan finds contamination about nine times in ten only when 10% of the units are contaminated. Test 20 units from a 10,000-unit lot in which 0.1% are contaminated, and the lot has a 98% chance of passing. USP’s <797> FAQs put the chance of detecting a contaminated preparation at about 10% for batches of 10 to 100, 4% at 250 and 2% at 500.

The same arithmetic applies to research vials. If 5% of the vials in a large batch are contaminated, a test of 2 vials finds the problem about 1 time in 10 (1 minus 0.95 × 0.95). A test of 20 vials finds it about 64 times in 100.

A pass on two vials means those two vials grew nothing. It cannot clear a batch.

Sterility testing methods: USP <71>, PCR and microbial counts

Shorter tests are also sold as “sterility”, and each answers a different question.

Method	What it detects	Time	Is it the USP <71> test
USP <71> culture	Visible growth of aerobic and anaerobic bacteria and fungi in two media	At least 14 days	Yes
Microbial count (TAMC, TYMC)	Colonies of bacteria and fungi that grow in air, counted as CFU	Plates read after 3–5 days (TAMC) and 5–7 days (TYMC)	No. It is a count for non-sterile products
PCR screen	Microbial DNA that the assay targets	Shorter than 14 days	No, unless validated as an alternative for that product
DNA microarray	DNA from the organisms on the array	Shorter than 14 days	No, unless validated as an alternative for that product
Short culture	Growth seen in the first days	A preliminary reading	No. It stops before day 14

Microbial counts. TAMC (total aerobic microbial count) and TYMC (total combined yeasts and moulds count) come from USP <61>, the harmonised test for non-sterile products. They count what grows under aerobic conditions and compare it with a limit. See bioburden vs sterility.

PCR and DNA screens. These look for microbial DNA in place of growth. A 2014 review in Applied and Environmental Microbiology notes that standard PCR is poor at telling DNA from a living cell apart from DNA from a dead cell or a free fragment. So a positive can come from dead organisms, and a negative covers only what the assay targets, above its detection limit.

Validated rapid methods. USP <1071> covers rapid tests for sterile products with a short life, where a 14-day result comes too late. USP <1223> sets out how a lab shows that an alternative method can replace the compendial one. Without that evidence for the product type, a rapid method is a screen, and the report should say so.

What peptide labs sell as sterility

Names and methods as shown on each lab’s own site in September 2026. Our comparison of sterility testing labs adds vials, reports and verification.

Lab	Test name on its site	What the method is
Krause Analytical	Sterility, 14-day – USP 71	USP <71>, as an add-on
Vanguard Laboratory	Sterility (USP 71, 14-day)	USP <71>, an option on every package; bioburden (USP 61) is a separate test
TrustPointe Analytics	USP <71> Sterility Test	USP <71>, 14–21 day lead time, 4–20 pooled vials
Bioviridian	Sterility Testing (USP <71>)	USP <71> by membrane filtration or direct inoculation, from 2 vials
Accumark Labs	Sterility USP <71>; Rapid Sterility Screening (PCR) Addon	USP <71> with a 14-day turnaround; a PCR screen sold as a separate add-on
Janoshik	Sterility testing (TAMC+TYMC)	A culture count over 14 days, reported as pass or fail, from 2 unopened vials
PharmLabs	Sterility & Microbial Screening (TAMC & TYMC)	A microbial count, with a published turnaround of 3–5 business days
Freedom Diagnostics	Sterility (PCR)	A PCR screen for microbial contamination, as the lab describes it
ILS Laboratories	Rapid Sterility Screen (DNA Microarray)	A DNA microarray screen for a broad panel of microbial contaminants

Accumark, PharmLabs, Freedom Diagnostics and ILS put the method in the test name, so a buyer can see what the test is. Accumark also sells the 14-day test next to its screen.

In our September 2026 review of public certificates from 25 labs and one rating site’s format, none showed a documented 14-day USP <71> test with the number of units, and one showed it in part. Labs that sell USP <71> may show it in full on reports we did not see.

Before you order a sterility test

• Ask for USP <71> or Ph. Eur. 2.6.1 by name, and for the technique: membrane filtration or direct inoculation.
• Send sealed vials in the number the lab asks for. A vial opened for another test no longer represents the product as sold.
• Check the report for the number of units, both media, method suitability, negative controls and incubation dates at least 14 days apart.
• Expect growth or no growth for each medium, with a line saying the result covers only the units tested.
• For any shorter test, look for the method name, its targets, its detection limit and the word “screen”.

Our page on how to read a COA covers the rest of the report.

What HK Analytical runs

Our sterility test is named Sterility (USP <71>, 14 days). It reports whether microbes grew from the tested units under USP <71> conditions during at least 14 days, and it cannot show that a whole batch is sterile. It needs its own unopened vials. Ask how many when you request a quote. We do not offer microbial screens or bioburden. Results within days of receipt. Sterility (USP <71>, 14 days) is the one test that takes 14 days, because the method incubates for 14 days. Every number comes with its raw data, in a signed record you can check on /verify. See the example report, or add endotoxin and other tests to the same quote.