Key Health Numbers to Know If You Have Psoriatic Arthritis

When you’re living with chronic disease, it can sometimes feel like you don’t have enough answers — and other times, as though you’re bombarded by a flood of data and don’t know what to make of it. This may be particularly true if you’re living with psoriatic arthritis (PsA).

This type of arthritis is linked with psoriasis, a chronic skin and nail disease, and can cause joint swelling like rheumatoid arthritis, per Johns Hopkins Medicine. We still have a lot to learn about the disease: For instance, doctors don’t know what causes it, even though immunity, genes, and environment can play a role.

Psoriatic arthritis may be diagnosed with a range of tests, including an erythrocyte sedimentation rate test (which measures inflammation using red blood cells) or imaging like X-rays and skin biopsies. The disease can cause a wide range of symptoms, from painful joints to skin rash. Although this can feel overwhelming at times to track, there are key metrics that can help you monitor your disease state.

Here are five categories of health numbers to keep in mind if you have PsA — plus, how your doctor can help you interpret them and provide a big-picture view of your disease state.

Minimal Disease Activity (MDA)

Certain metrics tell your doctor about the state of your PsA. These are called “treatment targets” and one that your physician may look at is minimal disease activity, or MDA.

MDA was established in response to the lack of a consensual definition for the remission of PsA, per The Journal of Rheumatology. You are in MDA if you have met at least five of the seven criteria:

• Psoriasis on less than 3 percent of body surface area (measured as three palms of psoriasis on your body or less)
• 0-1 tender joint
• 0-1 swollen joint
• 0-1 tender enthesis (where your tendons and ligaments meet the bone)
• Pain score of 2 or less on a scale of 0-10
• Patient global score of 2 or less (this is your overall sense of how your disease is on a scale of 0-10)
• Functional score of 0.5 or less on a scale of 0-3

“If you are in MDA, we know that your longer term outcomes are better, including better quality of life and a longer time on the same therapy,” says Alexis Ogdie-Beatty, MD, Director of the Penn Psoriatic Arthritis and Spondyloarthritis Program at the University of Pennsylvania Perelman School of Medicine.

Disease Activity of Psoriatic Arthritis (DAPSA)

Another treatment target is the disease activity of psoriatic arthritis (DAPSA). This is a metric that can be used in a similar way as MDA.

DAPSA combines your tender joint count (out of 68 joints), swollen joint count (out of 66 joints), patient global assessment, patient pain assessment, and C-reactive protein measures. You can see an example of what this analysis may look like here.

That said, your doctor may use each of these measurements individually to assess your disease state as well. “Each of these individual metrics listed also has value,” says Dr. Ogdie-Beatty.

For instance, C-reactive protein (CRP) is a nonspecific marker of both acute and chronic inflammation that can be higher in patients with psoriatic arthritis, per a 2022 study in Rheumatology and Therapy. The study found that CRP was more commonly requested by rheumatologists than by dermatologists.

RAPID3

Although the Routine Assessment of Patient Index Data 3 (RAPID3) was initially developed in rheumatoid arthritis, this patient-reported index has been found useful in many rheumatic diseases — including PsA, per a 2018 study in Arthritis Care and Research.

The study found that RAPID3 is comparably informative to DASPA in PsA, though with potentially greater feasibility for routine clinical care.

A RAPID3 assessment is collected when you answer three main questions about your physical functioning, pain, and patient global estimate (remember, this is a measure of your overall well-being).

“Patient-reported outcomes such as the RAPID3 result in a number that tells us overall how you’re doing and can be really helpful in tracking disease over time,” says Dr. Ogdie-Beatty.

That said, a 2019 study in RMD Open found that RAPID3 may not sufficiently capture changes in objective inflammatory signs in patients with rheumatoid arthritis. As with any other test, it’s best to use it as a puzzle piece that creates a bigger picture of your condition when combined with other qualitative and quantitative data.

Even though assessments like this one are designed for patients to be able to take on their own, they’re not meant to be interpreted alone. Share your RAPID3 score with your health care provider so they can monitor and track your disease activity.

Heart Disease Factors

Metrics that tie into cardiovascular risk are important to keep an eye on if you have psoriatic arthritis.

“Psoriasis and PsA are both associated with an increased risk for cardiovascular disease and having psoriasis actually increases the need for treating elevated cholesterol with a medicine like a statin,” says Dr. Ogdie-Beatty. “Ideally, patients have been screened for diabetes, have had their lipids checked, and know their risk for heart disease. We are currently testing new ways of making this easier for patients.”

Psoriatic arthritis patients have a higher prevalence of high blood pressure, diabetes, obesity, and elevated cholesterol (and therefore of metabolic syndrome) — and insulin resistance is closely linked to psoriatic arthritis, per a 2020 study in Joint Bone Spine.

While obesity has been shown to be a risk factor for psoriatic arthritis, some research also suggests that weight gain may be a result of inflammatory conditions, since patients with joint dysfunction may be less active, per a 2020 study in Rheumatology and Therapy.

What’s more, previous research has reported higher prevalence of obesity in psoriatic arthritis than in rheumatoid arthritis or psoriasis (6 percent vs. 4.4 percent vs. 3.8 percent).

“We’re not exactly sure why, but if a patient is carrying a lot of extra weight, they seem to be more susceptible to developing psoriasis and psoriatic arthritis,” says Christopher Morris, MD, a rheumatologist in Kingsport, TN.

Liver Abnormalities

In a 2023 study published in The Journal of Rheumatology, 32 percent of 1,061 psoriatic arthritis patients had liver abnormalities. On average, these abnormalities were detected after a follow-up duration of about 8 years.

The common causes of liver abnormalities were drug-induced hepatitis and fatty liver. Other independent factors associated with liver abnormalities were the following:

• Higher BMI
• Daily alcohol intake
• Higher damaged joint count
• Elevated CRP
• Use of methotrexate (MTX), Leflunomide (LFN) or TNF inhibitors

“We don’t know why, but when someone has psoriatic arthritis and they’re on a drug like methotrexate, there seems to be a higher incidence of liver abnormalities and complications than with people in rheumatoid arthritis,” says Dr. Morris. “It’s going to be important for these patients to have tests done looking at their liver and monitored very regularly.”

Numbers You Don’t Need to Worry About

One number that may not be as crucial: red cell distribution width (RDW). This test measures the differences in the volume and size of red blood cells and is often included in complete blood count tests, per the National Library of Medicine.

“We get so many emails about this being abnormal,” says Dr. Ogdie-Beatty. “Unfortunately, this is not that helpful but is frequently abnormal and gets reported and flagged, so it makes people uncomfortable.”

And, overall, none of these metrics alone should cause alarm. They are simply tools that you can use to track your disease activity and have informed conversations with your doctor. This can help you both make decisions about treatment.

Bring the numbers to your doctor, ask questions, and be sure to look at the big picture. These key health metrics aren’t meant to cause you stress or to be interpreted by you alone: After all, no single number can accurately reflect your disease state or quality of life.

The Psoriatic Arthritis Club

The Psoriatic Arthritis Club podcast series delves deep into the ups and downs of living with PsA. Through intimate conversations with fellow patients and insights from leading experts, the series offers valuable information on how to manage symptoms, collaborate with healthcare providers, advocate for better care, and emotionally cope with the disease. Along the way, listeners will also pick up life hacks, tips, and tricks to live better with psoriatic arthritis.