Read the report before reading the headline result
Start with the laboratory name, report identifier, client, sample description, lot or batch information, received and testing dates, method, and result. These details connect the number to a sample and a procedure.
A percentage or pass result without a clear sample identity and method is difficult to interpret. The laboratory can only report what it received and tested.
Each test answers one question
Identity asks whether the tested material is consistent with the expected compound under the method used. Purity estimates how much of the method’s measured signal is attributed to the target rather than detected related components or impurities.
Quantity, assay, or net-content testing estimates how much target material is present in the tested sample. A high purity percentage does not establish the total amount. For example, a small amount of highly pure material can still be less material than the label claims.
Sterility and endotoxin are not the same
A sterility test looks for viable microorganisms under defined test conditions. A bacterial endotoxin test looks for endotoxins associated with certain bacteria.
Endotoxins can remain even when living bacteria are absent, and FDA notes that most sterilization methods do not inactivate endotoxins. A sterility result therefore cannot stand in for endotoxin testing, and an endotoxin result cannot stand in for sterility testing.
The sample-to-batch connection matters
A laboratory result applies directly to the sample tested. Extending it to a batch requires confidence that the sample was correctly identified, collected, stored, and representative of that batch.
Representative sampling and chain of custody do not make a result perfect, but they help answer whether the tested material reasonably corresponds to the product being discussed.
Laboratory competence has a scope
ISO/IEC 17025 is a standard laboratories can use to demonstrate technical competence and the ability to generate valid results. Accreditation is meaningful, but it should be checked for the relevant laboratory, method, and scope—not treated as a universal badge covering every test.
Method suitability, controls, detection limits, reference materials, and uncertainty can all affect what a result supports.
Key terms
- Identity
- Whether the sample’s measured characteristics are consistent with the expected compound.
- Purity
- The target’s share of what a specific analytical method detects; its meaning depends on the method.
- Quantity / assay
- An estimate of how much target material is present in the tested sample.
- Sterility test
- A test for viable microorganisms under defined test conditions.
- Endotoxin test
- A separate test that detects or quantifies bacterial endotoxins.
- Specification
- A test, its method, and the acceptance criterion the result is compared with.
Relay diagram
Five questions—not one quality score
What this can—and cannot—tell us
What it can tell us
- Which tests were performed on the submitted sample and what results were reported.
- Whether the results met stated acceptance criteria, when criteria are provided.
- Which laboratory, method, dates, and identifiers support the report.
What it cannot establish alone
- Anything about a test that was not performed.
- That every unit in a batch—or a different batch—is identical to the tested sample.
- That a product is safe, effective, approved, correctly stored, or appropriate for use.
- That a purity percentage equals the labeled quantity.
Go deeperOptional · about 1 minute
Why purity and quantity can disagree
Chromatographic purity is often expressed as a percentage of detected peak area. That can be useful for comparing the target signal with other detected signals under the method.
It is not automatically a measurement of total mass. Water, salts, residual solvents, or components not detected in the same way may not be represented by that percentage. Quantity needs an appropriate assay or content method.
What a strong COA usually makes visible
FDA’s discussion of active-ingredient COAs includes the material name, grade, batch or lot number, release date, each required test, acceptance limits, and numerical results. A report should also make the issuing laboratory and authorization clear.
More fields do not guarantee truth, but missing identifiers and methods make independent interpretation and verification harder.
The takeaway
If you only remember one thing from this guide:
A COA describes the tests performed on one submitted sample. It is not a universal guarantee about every quality question or every product with the same label.
Sources and support7 sources
- CGMP Questions and Answers: Control of Components and Drug Product Containers U.S. Food and Drug Administration
Lists core COA fields including material, batch or lot, tests, acceptance limits, and numerical results.
- IND Chemistry, Manufacturing, and Control Information U.S. Food and Drug Administration
Separates identity, purity, strength, sterility, pyrogenicity, endotoxin, and other quality tests.
- General Chapter <71>: Sterility Tests U.S. Pharmacopeia
Describes sterility testing under aseptic test conditions.
- Bacterial Endotoxins/Pyrogens U.S. Food and Drug Administration
Explains bacterial endotoxin testing and its distinct purpose.
- The Bacterial Endotoxins Specification — Points to Consider U.S. Food and Drug Administration
States that most sterilization methods do not inactivate endotoxins and describes test, method, and acceptance criteria.
- ISO/IEC 17025 — Testing and calibration laboratories International Organization for Standardization
Explains the standard’s role in demonstrating laboratory competence and valid results.
- 21 CFR 211.84 — Representative sampling and testing Electronic Code of Federal Regulations
Supports the importance of representative samples and lot-specific testing.