Supplement labels tell you what a company says is in the bottle. A certificate of analysis, usually called a COA, tells you what a lab found when it tested a specific batch. More brands now post COAs on their websites or send them on request, and they’re one of the most practical quality checks available to shoppers.
They can also be confusing. COAs are written for quality-control staff, full of abbreviations, units, and test method codes. This guide explains how to read one and what to watch for.
What a COA Is (and Isn’t)
A COA is a document summarizing test results for one production lot of a product. In the U.S., FDA manufacturing rules for dietary supplements require companies to set specifications for identity, purity, strength, and composition and to verify they’re met. A COA is how those results are usually reported.
Some important distinctions:
- Raw material COA vs. finished product COA. Ingredient suppliers send COAs for raw materials. That doesn’t confirm the finished capsule you bought was tested. The most useful COA covers the finished product.
- In-house vs. third-party testing. A company can test its own products. An independent laboratory adds a layer of accountability.
- COA vs. certification seal. A COA is a single batch report. A certification program, such as those covered in our guide to third-party testing seals, typically includes facility audits, ongoing testing, and label review. They complement each other.
Anatomy of a COA: Section by Section
1. Header information
Look for:
- Product name and lot (batch) number. This is the most important check. The lot number should match the number printed on your bottle, usually near the expiration date.
- Dates: manufacture date, test date, and expiration or retest date.
- Laboratory name and contact details. If a third-party lab did the testing, it should be named.
2. Identity
Identity tests confirm the ingredient is what it claims to be, for example the correct plant species or the right chemical form of a vitamin. Common methods include HPTLC (a fingerprinting technique for botanicals), FTIR, HPLC, or DNA-based methods. A result like “Conforms” or “Positive” is normal here.
3. Potency (assay)
This section shows how much of each active ingredient was measured compared with the label claim. You’ll usually see the specification, such as “90-130% of label claim,” next to the measured result.
How to interpret it:
- Slightly above 100% is common. Manufacturers often add an “overage” so that potency stays at or above the label amount through the shelf life, since some nutrients degrade over time. Results of roughly 100-125% are typical for many vitamins.
- Well below 100% on a recent test is a red flag, especially for ingredients that should be stable.
- Large overages matter for some nutrients. A vitamin D product labeled 2,000 IU that tests at 125% delivers about 2,500 IU, still below the adult upper limit of 4,000 IU/day. But overages can matter for nutrients you get from several products, such as vitamin A, vitamin B6, or iron. Our upper limits guide lists the ceilings.
4. Contaminants: heavy metals
Most quality COAs test for the four main toxic elements: lead, arsenic, cadmium, and mercury. Results are usually given in parts per million (ppm), micrograms per gram (µg/g, the same as ppm), or parts per billion (ppb).
Things to check:
- Units and limits. A result of “<0.05 ppm” means the level was below that amount. Look at what limit the company uses. Many quality programs base limits on daily exposure, measured in micrograms per day, at the product’s recommended serving.
- “ND” (not detected) should be paired with a detection limit (LOD) or quantitation limit (LOQ). “ND” with a high detection limit is less reassuring than it sounds.
- Higher-risk categories include botanicals, protein powders, greens powders, cacao, rice-based ingredients, and minerals from natural sources. Our guide to heavy metals in supplements covers why.
5. Contaminants: microbes
Microbiological tests check for contamination during growing, processing, or packaging. Standard tests include:
- Total aerobic microbial count and total yeast and mold, usually reported in colony-forming units per gram (CFU/g) with a maximum limit.
- Specific pathogens, such as E. coli, Salmonella, and Staphylococcus aureus, which should be reported as “Absent” or “Negative.”
Probiotics are a special case. Their total count is meant to be high, so the COA should report the probiotic count separately from contaminant tests.
6. Other tests you may see
- Pesticides and residual solvents, common for herbal extracts.
- Allergen testing, such as gluten or soy.
- Disintegration or dissolution, which shows whether a tablet breaks down in a reasonable time.
- Moisture or water activity, which affects shelf stability.
Product-Specific Checks
Fish oil and omega-3s. Look for oxidation markers: peroxide value (PV), anisidine value (AV), and TOTOX, a combined score. Lower is fresher. Industry voluntary limits are commonly cited as PV of 5 meq/kg or less, AV of 20 or less, and TOTOX of 26 or less. Also check that EPA and DHA amounts match the label. See our omega-3 page for typical doses.
Probiotics. Check whether the CFU count is guaranteed “at time of manufacture” or “through expiration.” Live counts fall over time, so a through-expiration guarantee is more meaningful.
Protein powders. Look for heavy metal results per serving, and protein content measured directly rather than calculated only from the formula.
Botanicals. Identity testing matters most here, since adulteration and species substitution are known problems. Standardized extracts should report the marker compound, for example “withanolides, 5%.”
Red Flags
- No lot number, or a lot number that doesn’t match your bottle.
- “Pass” with no numbers. You should see measured values next to specifications.
- Every result exactly 100% of label. Real lab data has natural variation.
- Very old test dates, or a single COA used for years of production.
- A lab you can’t identify or verify. Accredited labs, often listed as ISO/IEC 17025, are easy to look up.
- Signs of editing in a PDF, such as mismatched fonts or alignment.
- Refusal to share without a reason. Some companies don’t publish COAs online, but a reputable brand should be willing to answer questions about testing.
What a COA Can’t Tell You
A clean COA confirms that a batch contained what it claimed without measurable contamination. It doesn’t tell you:
- Whether the supplement works. Efficacy depends on research about the ingredient and dose, not batch testing.
- Whether it’s right for you. A well-made product can still interact with medications or be inappropriate during pregnancy or with certain health conditions.
- Whether the dose is sensible. A product can test exactly at label claim and still deliver more than you need, especially if you take several supplements containing the same nutrient.
How to Request a COA
- Find the lot number on your bottle.
- Check the brand’s website for a COA lookup or “quality” page.
- If there isn’t one, email customer service with the product name and lot number and ask for the finished-product COA, including heavy metal and microbial results, and the name of the testing lab.
- Compare the results against the checks above.
Safety Notes
- Quality testing doesn’t remove interaction risks. For example, St. John’s wort interacts with many medications, and vitamin K affects warfarin, no matter how clean the batch. See our guide to supplement-drug interactions.
- If you’re pregnant or nursing, contaminant testing matters even more. Prefer products with published heavy metal results and talk to your provider about which supplements you need.
- Stop a product and contact your clinician if you have an unexpected reaction, and consider reporting it to the FDA’s adverse event reporting system.
Bottom Line
A certificate of analysis is a batch-specific lab report and one of the best tools for judging supplement quality. Match the lot number, look for actual numbers next to specifications, check heavy metals and microbes with their units and limits, and favor independent, accredited labs. A good COA shows a product was made well. It doesn’t show the product works or is right for you.
This article is for educational purposes only and is not medical advice. Consult a healthcare provider before starting any supplement, especially if you are pregnant, nursing, taking medication, or managing a health condition.