All medical testing is at best only an estimate. Example: There are people with severe lupus or other autoimmune disease, who show up in testing with normal ANAs, at times.

There are people with no obvious autoimmune issues, who will test positive for ANA, at times.

Medical testing is only a snapshot in time. The body changes, goes thru cycles, and even people with the same disorder, can have very different test results for it.

The statistical ranges are estimates. People are chosen who have no symptoms of a disorder, typically. But they are all different genetically from each other. Some may have smoldering issues, not yet identified.

Good doctors know this, and retest after a time period, and perhaps even again, later. Labs make mistakes, people make mistakes.

So testing is just a tool. An imperfect one at that.