Most people's first instinct, opening a certificate of analysis, is to scroll straight to the purity percentage. That's understandable — it's the biggest number on the page, usually in bold, sometimes in green. It's also the least useful field to check first.

1. Lot Code and Sample Code

These two identifiers tie the certificate to one specific batch, tested on one specific day. A COA with no lot code, or one that doesn't match what's printed on your vial, isn't necessarily fraudulent — but it means you can't actually confirm the paper you're holding describes the product in your hand. Always check that the lot code on the certificate matches the lot code on the label.

2. Received and Published Dates

The gap between when a lab receives a sample and when it publishes results tells you something about testing depth. A same-day turnaround on a full purity, identity, and sterility panel is unusual; most legitimate multi-day testing reflects the reality that some assays — sterility screening in particular — take time to run properly.

3. Method and Specification

This is the field most COAs skip, and it's the one worth asking a supplier about directly if it's missing. “>98.0%” is a specification, not a result — it tells you the bar the lab was testing against, which helps you judge whether 99.1% is a comfortable pass or a photo finish.

4. Quantity, Not Just Purity

A vial can be 99% pure and still underfilled. Total quantity — reported in milligrams, checked against what the label claims — catches a different failure mode than purity testing does. The two numbers answer different questions: purity asks what's in the vial; quantity asks how much of it there is.

5. Sterility and Endotoxin Status

These are frequently the last rows on the page, and frequently the ones marked “pending” — because they take longer to result than purity testing does. A pending sterility result isn't automatically a problem. A COA that omits the row entirely, rather than marking it pending, is a bigger one: it suggests the test either wasn't run or wasn't disclosed.

None of this requires a chemistry background. It requires reading past the number everyone's trained to look at first.