How to Read a Certificate of Analysis for Supplements

A certificate of analysis is the document that tells you what is actually in your supplement, as measured by an independent laboratory. It is one page, usually dense with numbers and abbreviations, and most people have never seen one. If you have never asked a supplement company for their CoA, you have been trusting labels without verification. That is normal, but it is not necessary.

What a Certificate of Analysis Is and What It Cannot Tell You

A CoA is a laboratory report documenting the results of specific tests performed on a specific batch. It typically covers three areas: identity (confirming the product is what it claims), potency (confirming it contains the claimed amounts), and purity (confirming contaminants are below acceptable limits).

A CoA is not a safety guarantee. It is a snapshot of one batch at one point in time. It does not tell you about storage conditions after testing, consistency across batches, or anything about batches that were not tested. But it is the most concrete evidence you can access as a consumer, and it is far more informative than marketing copy.

Who Performed the Testing: Why the Laboratory Matters

The first thing to check is who did the testing. A CoA from the manufacturer's own in-house lab is less independent than one from a third-party laboratory. Third-party testing means the company sent their product to an external, accredited laboratory with no financial relationship to the outcome.

Look for the laboratory name, accreditation number, and testing date. In the UK, UKAS accreditation is the recognised standard. Internationally, ISO 17025 accreditation covers testing and calibration laboratories to a comparable level. If no laboratory is named anywhere on the document, what you are looking at is not a genuine CoA.

How to Read the Potency Section of a Supplement CoA

For omega-3 supplements, the potency section should list the EPA and DHA content per serving as measured by the laboratory. Compare these figures to what the label claims. Minor variations of 10 to 15 per cent from label claims are normal in natural products.

Significant shortfalls suggest the product is underdosed. Published testing surveys have found that multiple commercial omega-3 products failed to deliver the EPA or DHA amounts stated on their labels. Label accuracy is a real and documented problem across the supplement industry, not a theoretical one.

For chlorella or marine phytoplankton supplements, potency testing might cover protein content, chlorophyll, carotenoids, or EPA depending on the product's claims. The tested parameters should match the claims the product makes on its label.

One red flag we learned to watch for: results that exactly match label claims with zero variation. Real analytical measurements of natural products always produce some variance. If the numbers on the CoA are identical to the numbers on the label, down to the decimal, the document may have been written from the label rather than from a laboratory.

How to Read the Heavy Metal Section of an Algae Supplement CoA

This is the section most relevant to algae supplements. We covered the full contamination picture in our guide to heavy metals in algae supplements. The four metals you should see tested are lead, cadmium, arsenic, and mercury.

Lead, Cadmium, and Mercury: Reading the Numbers

Lead (Pb): the EU limit for food supplements is 3.0 mg/kg. Many quality products test below 0.5 mg/kg. Lower results give you more confidence in the product's purity.

Cadmium (Cd): the EU limit is 1.0 mg/kg for food supplements, 3.0 mg/kg for seaweed-based products. Cadmium accumulates in the kidneys over years of exposure, so lower results are preferable.

Mercury (Hg): the EU limit is 0.1 mg/kg. Less commonly a concern for cultivated algae than for fish-derived products, but should still be tested.

Arsenic: Why Speciation Matters

Arsenic on a CoA requires more scrutiny. Check whether the result shows total arsenic or inorganic arsenic. Marine-origin products may show elevated total arsenic that includes less-toxic organic forms like arsenosugars. Inorganic arsenic is the fraction of primary health concern.

In some algae food products, inorganic arsenic was up to 62 per cent of total arsenic (Almela et al., J Agric Food Chem, 2002). In others, the inorganic fraction was negligible. A total arsenic figure without speciation is harder to interpret. There is no EU or UK limit for arsenic in food supplements, which makes your own scrutiny the only safeguard.

Understanding Detection Limits: The Most Overlooked Number on a CoA

A result of "not detected" or "ND" is only meaningful if you know the detection limit. If the laboratory's limit for lead is 10 ppm, "not detected" means "less than 10 ppm." The EU limit is 3 ppm. A detection limit above the regulatory threshold renders the result meaningless for safety purposes.

The detection limit (sometimes called "limit of detection" or LOD) should be stated on the CoA, usually in the same column as the result or in a footnote. If it is not stated, the "not detected" result is uninterpretable. ICP-MS testing routinely achieves detection limits of 0.001 to 0.01 mg/kg. You need the limit to be at least ten times lower than the regulatory threshold for genuine reassurance.

Microbial Testing on a Supplement CoA

For whole-food supplements like phytoplankton and chlorella powders, microbial testing is relevant. Standard parameters include total aerobic plate count, yeast and mould, coliforms, E. coli, and Salmonella. The presence of E. coli or Salmonella at any level is a failure.

Microbial contamination risk is higher in products from open-pond cultivation, where environmental organisms can enter the culture. Products from closed photobioreactors have lower microbial risk at source, though post-harvest handling still matters.

How to Read a Certificate of Analysis FAQs

What are the red flags on a supplement certificate of analysis?

Six warning signs: no laboratory name or accreditation on the document; no batch number linking results to a specific production run; "not detected" results without stated detection limits; only one or two metals tested when four are standard; results that exactly match label claims with no variance; and a testing date years before the product expiry with no more recent documentation.

How do I request a certificate of analysis from a supplement company?

Email customer service with your batch number and ask for the third-party testing results for that batch. A company that responds promptly with a batch-specific, independently tested document is giving you what you need. A company that provides a generic undated document or does not respond is asking you to trust the label on faith.

Is a CoA from the manufacturer's own lab trustworthy?

In-house testing is better than no testing, but it lacks independence. The manufacturer has a financial interest in the result. Third-party laboratories with UKAS or ISO 17025 accreditation follow standardised methods and have no commercial stake. If you are comparing two products, the one with independent third-party testing provides stronger evidence.

What does "not detected" mean on a CoA?

It means the substance was below the laboratory's detection limit for that test. The critical question is what that limit was. "Not detected" at a limit of 0.01 mg/kg is genuinely reassuring. "Not detected" at a limit of 10 mg/kg tells you almost nothing. Always check the stated detection limit before treating "not detected" as a clean result.

Does Phytality provide certificates of analysis?

Yes. We test every batch through independent laboratories using ICP-MS for heavy metals and standard microbial panels. Results include detection limits alongside each measurement. We make these available on request because we consider batch-level transparency a baseline for this product category.

This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Consult your GP or a qualified healthcare professional before starting any supplement.

Methodology and Disclosure

EU maximum contaminant levels cite Commission Regulation (EC) No 1881/2006 as retained in UK law. Arsenic speciation data cites Almela et al. 2002 (J Agric Food Chem). Laboratory accreditation standards cite ISO/IEC 17025:2017. Detection limit guidance reflects standard ICP-MS capabilities as reported in published analytical literature.

Vendor disclosure: Phytality is the publisher of this article and the manufacturer of algae-based supplements. We test every batch through independent laboratories and publish results with detection limits. Our interest in CoA transparency is both editorial and commercial.