Guides / How to read a COA
How to read a supplement COA
Updated 4 November 2026 · BatchAssay editorial
In short
- A COA (certificate of analysis) is a lab's measurement of a specific sample — the only public document that shows what is actually in a supplement.
- Check five things: who tested (accredited lab), which batch, when, against which limits, and whether the actives were measured.
- Red flags: no batch number, no lab name, results older than ~18 months, edited PDFs, and "representative" samples instead of the batch you can buy.
1. Who did the testing?
A COA is only as good as the lab behind it. Look for an ISO/IEC 17025 accredited laboratory — in Europe that means accreditation by a national body such as DAkkS (Germany), RvA (Netherlands) or UKAS (UK), usually shown as a logo with a registration number on the report. A report from the manufacturer's own in-house lab is better than nothing, but it is not independent. A report with no lab name at all is not evidence.
2. Which batch was tested?
Supplements are made in batches, and contamination varies per batch — one harvest of ashwagandha root can be clean while the next carries lead from the soil. A real COA names a batch or lot number that you can match against the number printed on your jar. A report without one tells you about some sample the brand once submitted, not about the product in your hand. This matters enough that we wrote a separate guide on it: why batch numbers matter.
3. When was it tested?
A 2021 report proves nothing about a 2026 batch. We treat results as current for about 18 months; after that a verified status expires on this site. If a brand's newest published report is years old, that is a sign testing happened once for marketing, not as routine quality control.
4. What limits are the results compared against?
Numbers mean nothing without limits. For heavy metals in EU food supplements the legal maximums are lead 3.0, cadmium 1.0 and mercury 0.1 mg/kg (Regulation (EU) 2023/915). Arsenic has no EU limit for supplements — a gap worth knowing about. A good report states each result, the limit, and whether it passed; the best ones also state the LOQ (limit of quantification — the smallest amount the method can measure, so "< LOQ" means "below what we can detect"). Our guide to the EU limits walks through all of them.
5. Were the actives measured?
Safety testing says what is not in the product; potency testing says what is. For extracts this is where the money is: withanolides in ashwagandha, curcuminoids in turmeric, fulvic acid in shilajit, beta-glucans (not just polysaccharides — starch counts as those too) in mushroom extracts. A brand that pays for active-content testing is showing you the product does what the label claims.
Red flags
- No batch number — see point 2; this is the most common and most important gap.
- No lab name or accreditation — unverifiable by definition.
- "Representative sample" — the sample may not be the batch sold to you.
- Edited PDFs — reports that show signs of image-editing software in their metadata. Labs issue PDFs directly; there is no honest reason for a COA to pass through Photoshop.
- Cropped screenshots of reports, with headers or footers cut off.
- Only an organic/GMP certificate offered where a lab analysis was asked for.
FAQ
What does COA stand for?
Certificate of analysis: a lab's report of what it measured in a specific sample — heavy metals, microbiology, actives, or all three. It is evidence, not a marketing badge.
Is a COA the same as an organic or GMP certificate?
No. Organic, GMP, ISO 9001 and similar certificates describe how a product is made, not what is in it. Only a lab analysis of the actual product tells you about contamination or potency.
The brand says 'lab tested' but shows no report. Does that count?
No. A claim without a published report is unverifiable. Many brands that genuinely test publish nothing — which is their choice, but it leaves you with nothing to check.
Can a good COA guarantee a supplement is safe?
No single document can. A current, batch-matched, accredited COA showing results well under the limits is the strongest public evidence available — but it covers the analytes tested, nothing more.
Sources
- Regulation (EU) 2023/915 on maximum levels for certain contaminants in food
- ISO/IEC 17025 — general requirements for testing and calibration laboratories
- BatchAssay methodology — the exact checks we run on every report
Information only, not medical advice. Methodology