New Inflammation Biomarker May Be Useful in AS, Study Suggests

Ratio of blood proteins fibrinogen, albumin can measure inflammation severity

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by Steve Bryson PhD |

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The ratio of two blood proteins, fibrinogen and albumin, accurately measures inflammation severity with different types of spondyloarthritis (SpA), including ankylosing spondylitis (AS), a study showed.

The accuracy of this biomarker closely matched those of standard inflammatory markers used in research and clinical practice. Further studies are needed to standardize this test and investigate the role of the fibrinogen-to-albumin ratio in inflammation, the researchers noted in the study, “The potential value of fibrinogen to albumin ratio (FAR) in the assessment of inflammation in spondyloarthritis,” which was published in BMC Musculoskeletal Disorders.

Spondyloarthritis is a group of inflammatory diseases affecting the joints and spine and includes AS, which is marked by inflammation of the sacroiliac joints, where the spine joins the pelvis.

Biomarkers reflecting inflammation are necessary to help clinicians gauge disease activity and guide treatment. Blood-based biomarkers C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) are generally used to assess inflammation.

Albumin is a blood protein that helps transport molecules through the bloodstream and has been used as a biomarker to predict the severity of inflammation in certain conditions. Fibrinogen, a protein that helps blood clots form, can also indicate inflammatory activity.

Thus, measuring the fibrinogen-to-albumin ratio (FAR) may be a more specific and sensitive method to evaluate inflammation severity with different forms of spondyloarthritis.

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Biomarker levels in spondyloarthritis, osteoarthritis

Researchers in China examined blood test results from 196 people with spondyloarthritis, 66 with the degenerative bone disease osteoarthritis, and 81 unaffected people who served as controls.

The spondyloarthritis group included 80 AS patients, 69 with psoriatic arthritis, a type of arthritis with skin patches (psoriasis), and 47 with reactive arthritis, where an infection triggers joint pain and swelling.

Compared with osteoarthritis patients, those with spondyloarthritis had elevated CRP, ESR, and fibrinogen, as well as lower albumin, supporting “that SpA patients had undergone more serious inflammatory reactions,” the researchers wrote.

Levels of these markers, including FAR, were also significantly different in spondyloarthritis patients than controls, despite the two groups being matched in age, gender, and white blood cells count.

Among the spondyloarthritis group, AS patients were more frequently younger men with lower CRP, ESR, and FAR levels than those with reactive arthritis — a group marked by older age, more women, and severe inflammation. No differences were seen between psoriatic arthritis patients and the AS group.

Albumin, fibrinogen, and FAR all strongly correlated with the widely used CRP and ESR biomarkers. Higher fibrinogen, FAR, and lower albumin was significantly associated with worsening CRP and ESR measures. After adjustments, only fibrinogen and FAR remained significant predictors for CRP and ESR, however.

The diagnostic accuracy of both fibrinogen and FAR was 95%, considered excellent and similar to 94% with CRP and ESR. With a FAR value above 9.44, the ability of FAR to correctly identify inflammation (sensitivity) was 91%, while below this cutoff, FAR was able to rule out inflammation (specificity) with 88% accuracy.

For fibrinogen, with a cutoff value of 3.98 grams per liter of blood, the sensitivity was 85% and the specificity 94%. The accuracy of fibrinogen and the FAR assessment was slightly lower under conditions of mild inflammation, but the test was “still valuable,” the researchers noted.

“The study shows the ability of FAR in evaluating inflammation, which is related to ESR [and] CRP,” the researchers said. “Further exploration of the direct relationship between FAR and SpA disease activity is expected, and an assessment standard including FAR is worth studying.”