Meet Sarah. She's not a real patient, but I've seen her story many times.
Sarah is 42 years old. For the past year she's had over an hour of morning stiffness in both hands, the kind that loosens up as the day goes on. Her knuckles are swollen. Some days her wrists ache enough to make simple tasks difficult.
She saw her primary care doctor, who did the right things — checked for inflammation, ran rheumatoid factor and anti-CCP antibody. Everything came back normal. She was told everything was normal and was reassured.
But she still feels terrible.
What those labs are actually testing
When a doctor suspects rheumatoid arthritis (RA), they'll typically order a couple of specific blood tests. The two most common are rheumatoid factor (RF) and anti-CCP antibodies. These are called serologies, proteins the immune system produces that can suggest RA is present. When they're positive, we call it seropositive RA.
But here's the thing: the labs don't tell the whole story in either direction.
Not everyone with RA has positive serologies. Somewhere between 20 and 30 percent of people with RA are seronegative, meaning their labs come back normal even though the disease is active. The joints are inflamed. The damage can still happen. The bloodwork just doesn't show it.
And on the flip side, a positive RF or anti-CCP doesn't automatically mean you have RA either. Both can show up in other conditions, and some people have positive serologies with no joint disease at all. A positive result raises suspicion. It doesn't make the diagnosis.
So how do we actually diagnose RA?
RA is a clinical diagnosis. That means it comes from putting the whole picture together, not from a single test result. When I'm evaluating someone for RA, I'm thinking about:
- Which joints are involved, and how many
- Whether there's swelling I can feel on exam
- The pattern of morning stiffness, how long it lasts, which joints are affected
- Whether symptoms are symmetrical (both hands, both wrists)
- Lab work, including RF and anti-CCP, but also inflammatory markers like CRP and ESR
- Sometimes imaging, X-rays or musculoskeletal ultrasound
The American College of Rheumatology has a formal scoring system that accounts for all of this. A patient can meet criteria for RA without a single positive lab value. The scoring system exists precisely because the labs don't always tell the whole story.
Does seronegative RA look different?
Somewhat. It tends to be harder to diagnose early on, partly because the labs don't give us that confirming signal, and partly because the presentation can be more variable. The presentation can be more subtle, with fewer joints involved and less obvious swelling, so it's easier to dismiss.
But seronegative RA is still real RA. It causes joint inflammation, can lead to damage over time if untreated, and responds to the same treatments we use for seropositive disease. The stakes of missing it aren't lower just because the labs are negative.
Back to Sarah
Sarah eventually saw a rheumatologist. Her RF was negative. Her anti-CCP was negative. Her CRP was unremarkable.
But on exam, several of her MCP joints (the knuckles at the base of the fingers) were swollen. Her morning stiffness lasted well over an hour. Ultrasound showed synovitis, inflammation inside the joint lining, in multiple joints.
She was diagnosed with seronegative RA and started on treatment. Over the next several months, things were better.
The labs were a reasonable place to start. But they weren't the end of the story.
The bottom line
If you've been told your labs are normal but your joints are still swollen, stiff, or painful, that's not necessarily the end of the story.
Rheumatoid arthritis doesn't always show up in bloodwork, especially early on. If your symptoms persist despite normal labs, that's exactly the kind of situation a rheumatologist is trained to evaluate. It's not that something was missed — it's that some diagnoses require a closer look.
A rheumatologist can examine your joints, put the full picture together, and tell you whether what you're experiencing might be seronegative RA.
The labs are one piece of the picture, not the whole thing.