For patients · 13 min · Worth watching
A positive ANA test is not a diagnosis — a rheumatologist explains
Dr. Diana Girnita, MD, PhD — Double board-certified rheumatologist; PhD in immunology; founder of Rheumatologist OnCall
A test result is not a diagnosis. That sentence is the most useful thing anyone in this field can teach a patient, and it generalises well past rheumatology.
Somebody arrives holding a piece of paper with a number on it and a search history full of the worst thing that number can mean. What a good clinician does next is explain what the test measures, what fraction of perfectly well people also return it positive, and what would have to be true alongside it to mean anything.
Why this one is on a biologics supplier's website
Because the same move is made constantly in our own category, in the other direction. A particle count, a cell viability figure, a certificate — each is a real measurement, and each is regularly presented as if it settled a question it does not touch. Watching a rheumatologist do this carefully with a blood test is good practice for reading a supplier's number.
What to watch for
- How often the answer is "this result alone tells you very little." That is what a measurement usually means, in any field.
- The base rate — how common the finding is in people with nothing wrong. Almost no marketing number is ever presented alongside its base rate.
