The fields that actually matter
A useful COA states the batch or lot number, the test date, the testing lab’s name, the testing method (HPLC is standard for peptide purity), and the measured purity percentage. Missing any of these weakens how much the document actually proves.
Batch number is the anchor
Without a batch number that matches what’s printed on the vial you receive, the COA could describe any batch, not necessarily the one in your hands. This is the single detail worth checking first.
Reading the purity figure in context
A high purity percentage on its own doesn’t tell the whole story; it needs to be paired with a stated, credible testing method. A number with no method behind it is harder to trust than a slightly less impressive number with a clear, checkable method stated.
Checking the lab itself
A named, independently searchable testing lab adds credibility that a generic or unnamed “third-party lab” reference doesn’t. Where possible, searching for the lab’s own name independently is a reasonable extra step.
Cross-checking against the vial
The batch number, mg content, and any dates on the COA should all match what’s printed on the physical vial. A mismatch, even a small one, is worth raising with the seller directly rather than assuming it’s a minor clerical error.