Key takeaways
- A certificate of analysis (COA) lists the tests run on one batch, or lot, of a product and what they found. Check that it covers the finished product and the lot number on your package.
- Heavy metals are usually reported in ppm, which for a powder means micrograms per gram. Multiply by the serving size in grams to get micrograms per serving.
- “ND” and “< LOQ” mean the amount was below what that lab’s method can detect or measure. Neither means zero, so look for the limit listed next to them.
- A quality seal means a product passed a program’s checks, but it doesn’t show your batch’s numbers. A vague “third-party tested” claim tells you even less.
What a certificate of analysis is
A certificate of analysis, or COA, lists the tests run on one batch of a product, the result of each test, and the limit it was checked against. It may come from a testing lab, an ingredient supplier or the brand itself.
The FDA doesn’t approve dietary supplements for safety or effectiveness before they’re sold.[7] Instead, manufacturers must set specifications for each product and check that they’re met. For some of those checks they can rely on a supplier’s COA, but only after qualifying the supplier, and they must confirm the supplier’s results from time to time. Dietary ingredients still need their own identity test.[2]
Some brands post COAs on their websites by lot number, and others send them if you ask. When you get one, check that it covers the finished product and the lot you bought.
The parts of a COA
COAs vary in layout. Here’s a sample with the parts to look for, each one numbered:
- Product · lot
- Vanilla protein powder · Lot 24-118
- Received · tested
- Oct 2, 2026 · Oct 6, 2026
| Test | 4Method | 5Result | Units | 6LOQ | 7Limit | 8Status |
|---|---|---|---|---|---|---|
| Lead | ICP-MS | 0.05 | ppm | 0.01 | ≤ 0.17 | Pass |
| Arsenic (total) | ICP-MS | 0.08 | ppm | 0.01 | ≤ 0.50 | Pass |
| Cadmium | ICP-MS | ND | ppm | 0.01 | ≤ 0.17 | Pass |
| Mercury | ICP-MS | < LOQ | ppm | 0.005 | ≤ 0.50 | Pass |
| Yeast and mold | Plate count | < 10 | CFU/g | 10 | ≤ 1,000 | Pass |
| Salmonella | PCR | Not detected | per 25 g | – | Absent | Pass |
| Protein | Combustion | 80.2 | % | – | ≥ 78 | Pass |
- Lab and accreditation
Who ran the tests, and whether the lab is accredited to ISO/IEC 17025 for them. Ask separately whether the lab is independent of the brand.
- Product and lot number
Should match the name and lot printed on your package. A COA covers one batch only.
- Dates
When the lab received and tested the sample. They should fit the batch you bought.
- Method
How each thing was measured. ICP-MS is a common method for metals.
- Result and units
The amount found. For metals in a powder, ppm means micrograms per gram.
- LOQ
The smallest amount the method can measure reliably. “ND” and “< LOQ” mean below what this lab could detect or measure, not zero.
- Limit
What the result had to meet: a maximum for a contaminant, a minimum for protein, or “absent” for a germ.
- Pass or fail
Whether each result met its limit. Look at the numbers too, not just the word “pass.”
- Sign-off
Who reviewed and approved the report, and when.
ISO/IEC 17025 sets requirements for a testing lab’s competence, impartiality and consistent operation.[5]
Turn ppm into micrograms per serving
Most COAs report heavy metals as a concentration. For a powder or other solid, one part per million (ppm) means one microgram (µg) in every gram. One part per billion (ppb) is a thousand times smaller: 1 ppm is 1,000 ppb.
Daily limits are written in micrograms, so you need the amount you actually take.
Here’s how one of those scoops a day compares with the benchmarks you’ll see most:
| Benchmark | Daily amount | 1.5 µg is |
|---|---|---|
| USP limit for dietary supplements | 5 µg | under the limit |
| California Prop 65 safe-harbor level (reproductive harm) | 0.5 µg | 3 times the level |
| FDA interim reference level, women of childbearing age | 8.8 µg from all food | about 17% |
| FDA interim reference level, children | 2.2 µg from all food | about 68% |
These benchmarks do different jobs. USP’s limit is for supplements taken at the most the label recommends in a day. It also sets daily limits of 5 µg for cadmium and 15 µg each for inorganic arsenic and total mercury.[8] Prop 65’s level decides when a product needs a warning label in California; going over it doesn’t on its own mean a product is unsafe.[9] The FDA’s levels cover everything you eat in a day, not one product, and they’re benchmarks, not safe allowances.[3]
What “ND” and “< LOQ” really mean
“ND” usually means not detected: below the smallest amount the lab’s method can detect. “< LOQ” means below the limit of quantitation: there may be a trace, but too little to measure reliably. Neither means zero.[10]
Too little for the method to detect.
Detected, but too little to measure reliably.
Measured, for example “0.05 ppm.”
What matters is how small the lab can go. Say a lab’s LOQ for lead is 0.1 ppm. On a 30-gram scoop, “< LOQ” means less than 3 µg of lead per serving, but not how much less. A lab with an LOQ of 0.01 ppm would narrow that to less than 0.3 µg.
Red flags on a COA
- The lot doesn’t match, or there’s no lot number at all.
- Contaminant tests with no number: just “pass” or “meets specification,” with no amount or units.
- Only a raw ingredient was tested. That doesn’t show what’s in the finished product you bought, so ask what testing covers your lot.
- Unclear lab credentials. Check that the lab is accredited for the tests listed. An accredited lab can still be the brand’s own, so ask whether an outside lab ran the tests.
- Old dates for a batch that was made recently.
- No heavy metal results. Ask the brand how it checked for lead, arsenic, cadmium and mercury.
- “ND” with no limit listed next to it.
COAs, seals and “third-party tested”
Seals from groups such as USP, NSF International and ConsumerLab.com mean a product was made properly, contains what the label lists and doesn’t have harmful levels of contaminants. They don’t guarantee that a supplement is safe or that it works.[6] And a seal doesn’t show the numbers for your batch.
- Passed a program’s checks
- Made properly, with what the label lists
- Doesn’t show the numbers for your batch
- Each test, method and result
- The limit each result was checked against
- Only covers the batch it names
“Third-party tested” on its own says even less. It doesn’t tell you what was tested, which batch, or what the results were. A COA does, so when a brand makes the claim, ask for the report.
Questions people ask
- What does ND mean on a certificate of analysis?
- ND usually means not detected: the amount was below the smallest amount that lab’s method can detect. It does not mean zero. Check the detection or quantitation limit listed next to it to see how small the lab could go.
- How do I convert ppm to micrograms per serving?
- For a powder or other solid, one ppm is one microgram per gram, so multiply the result in ppm by the serving size in grams. For example, lead at 0.05 ppm in a 30-gram scoop is 1.5 micrograms per serving. If the result is in ppb, divide by 1,000 first.
- How much lead is too much in a supplement?
- USP’s standard for dietary supplements sets a limit of 5 micrograms of lead a day. California’s Prop 65 safe-harbor level for reproductive harm is 0.5 micrograms a day. The FDA’s interim reference levels, 2.2 micrograms a day for children and 8.8 for women of childbearing age, cover all food combined and are benchmarks, not safe allowances.
- Is a certificate of analysis the same as third-party testing?
- Not always. A COA can come from a supplier, the brand’s own lab or an outside lab. Look for a lab accredited to ISO/IEC 17025 for the tests listed, ask whether it is independent of the brand, and check that the COA covers the finished product and your lot.
- Where can I find a product’s COA?
- Look on the brand’s website, or email the brand with the lot number from your package. If you can’t get one, you can’t check that lot yourself, though that alone doesn’t mean the product is unsafe.
Sources
- [1]U.S. Pharmacopeia. 〈2232〉 Elemental contaminants in dietary supplements. accessed October 2026.
- [2]Electronic Code of Federal Regulations. 21 CFR 111.75: What must you do to determine whether specifications are met?. accessed October 2026.
- [3]U.S. Food and Drug Administration. Lead in food and foodwares. accessed October 2026.
- [4]California Office of Environmental Health Hazard Assessment. Lead and lead compounds (Proposition 65). accessed October 2026.
- [5]International Organization for Standardization. ISO/IEC 17025:2017 General requirements for the competence of testing and calibration laboratories. 2017, confirmed 2023.
- [6]NIH Office of Dietary Supplements. Dietary supplements: what you need to know. accessed October 2026.
- [7]U.S. Food and Drug Administration. Questions and answers on dietary supplements. accessed October 2026.
- [8]U.S. Pharmacopeia. USP 〈2232〉 Elemental contaminants in dietary supplements (presentation). 2017.
- [9]California Office of Environmental Health Hazard Assessment. Businesses and Proposition 65. accessed October 2026.
- [10]U.S. Food and Drug Administration. Elemental Analysis Manual: terminology. accessed October 2026.
This article is for general information. It is not medical advice and does not replace a doctor, dietitian or pediatrician. Purus gives estimates for general information; it is not a medical device and does not diagnose, treat or prevent any condition.
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