What third party testing covers, and what it doesn't
Third party testing answers four separate questions: identity, potency, heavy metals and microbes. A certificate of analysis only covers the assays a brand ordered, so a single panel rarely settles all four. That gap is the whole story, and it's why two bottles with identical labels can sit at very different levels of verification.
The four questions, one at a time
Identity asks whether the bottle contains what the front says, and vitamin A is a case where the answer has range: retinyl palmitate, retinol acetate, or a plant carotenoid each print differently. Potency asks how much, measured against the 900 mcg RAE daily value adults use as an anchor. Heavy metals ask about lead, arsenic, cadmium and mercury. Microbes ask about the contamination that slips in during handling. Four panels, four methods, four costs.
A CoA listing only potency is genuine and still incomplete. You're allowed to read it that way.
Cost follows the same logic. Running four assays on one batch costs more than running one, which is why verification lives on a spectrum and the cheap end of the market prints so many badges. A badge is a claim about a process; a certificate is a claim about a batch. You want the second document.
Why vitamin A raises the stakes
Most nutrients fail gently; this one doesn't. The tolerable upper level for preformed vitamin A sits at 3000 mcg a day for adults, and chronic intake above it stresses the body in ways that don't announce themselves early. A batch that overshoots its label by a wide margin is a paperwork problem for most ingredients and a different conversation for this one. Potency verification isn't a formality here, it's the difference between 900 mcg and something you didn't plan on. The margin between the daily value and the ceiling is where careful manufacturing lives, and a 500 mg herbal powder printed loose doesn't face the same pressure.
What to ask a brand, in one email
Write and ask three things: which batch was tested, by which lab, and for which of the four questions. The reply tells you more than any badge on the packaging. A brand that supplies a third of the story, potency alone, is answering one question and hoping you forget the other three. Picture the two replies you might get back: one attaches a dated CoA naming the lab, the batch number and the assay list; the other sends a marketing PDF with no batch on it anywhere. The second isn't proof of a bad product. It's proof of nothing, which is a different thing.
Brands that test seriously answer within days and don't make you ask twice. Brands that dodge are telling you where verification sits in their priorities.
Where voluntary verification ends
Testing is voluntary across most of the market, so absence of a CoA isn't proof of a problem; it's an absence of evidence you're entitled to weigh. Ask how often batches are tested while you're at it. A brand that panels every run can speak for the bottle in your hand; a brand that tested once, years ago, is quoting history. A certificate also has a shelf life of sorts: it speaks for one batch, not the bottle sitting on your shelf a production run later. And no panel, however complete, tells you whether an ingredient suits your situation or how it sits with prescribed medication. That part stays with a clinician.
Send the email before you reorder, not after. One message, three questions, and you'll know which kind of brand you bought from.
Frequently asked questions
What does a certificate of analysis cover?Show answerHide answer
Whatever assays were ordered. Ask which were run before assuming anything.
Is testing legally required?Show answerHide answer
Verification is voluntary in most of the market, which is why brands differ so much.
What should I ask a brand?Show answerHide answer
Which batch was tested, by which lab, and for which four things.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
