Patients with rheumatoid arthritis (RA) and psoriatic arthritis (PsA) who had Power Doppler ultrasound (PDUS)-evident synovitis had higher levels of serum calprotectin and lower tumor necrosis factor inhibitor (TNFi) serum troughs, suggesting that these values may help identify patients with PDUS synovitis in clinical remission or low disease activity.1 These results, derived from a cross-sectional study, were recently published in Arthritis Research & Therapy. 

The use of musculoskeletal ultrasound (MSUS) to assess joint inflammation has become increasingly recognized as a a non-invasive diagnostic modality that is sensitive in detecting to synovial inflammation. The addition of Power Doppler (PD) to assess synovial vascularization has enabled clinicians to distinguish between synovial inflammation and hypertrophy.  Moreover, PD has been shown to correlate with both disease activity and response to treatment in RA.2

Serum levels of calprotectin, a heterodimeric complex of 2 calcium-binding myeloid-related proteins, have also been used as a sensitive biomarker of disease activity in patients with RA and patients with spondyloarthritis (SpA). Similarly, higher TNFi drug trough levels have also found to be correlate with treatment response secondary to improvements in disease activity. 

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High Yield Data Summary

  • Patients being treated with TNFis with RA and PsA who had PDUS-evident synovitis had higher levels of serum calprotectin and lower TNFi troughs
  • Calprotectin and TNFi troughs may serve as biomarkers of ultrasound-active synovitis in patients with RA and PsA who are in clinical remission or with low disease activity 

Therefore researchers sought to determine the accuracy of serum calprotectin and TNFi troughs in detecting the presence of PDUS synovitis in RA and PsA after low disease activity or clinical remission was achieved. 

Researchers analyzed consecutive patients diagnosed with RA and polyarticular PsA from a single arthritis center in a cross-sectional study.  

All patients were either in remission, as defined by the 28-joint Disease Activity Score based on erythrocyte sedimentation rate [DAS28-ESR] ≤2.6, or had low disease activity, as defined by DAS28-ESR ≤3.2, on 2 consecutive evaluations ≥3 months apart. 

Eligible study participants had taken either adalimumab (ADA), etanercept (ETN) or infliximab (IFX) for ≥3 months.

All study participants underwent clinical assessment with the 28-joint swollen and tender joint counts, physician global assessments, and patient global assessments with visual analogue scales prior to MSUS evaluation.  Synovial hypertrophy and Power Doppler were graded using a semi-quantitative system (0 = no, 1 = mild, 2 = moderate and 3 = severe), as previously published. 

Serum biomarker levels were taken from peripheral blood draws collected prior to next scheduled TNFi dose. Calprotectin levels were measured using an enzyme-linked immunosorbent assay (ELISA) methods.

A total of 92 patients were included in the final data analysis, 42 patients with RA and 50 patients with PsA. Of these patients, 71 (77.2 %) were in clinical remission, and 21 (22.8 %) had low disease activity.  Forty four were being treated with ETN, 32 with ADA, and 16 with IFX. Median during of treatment with biologics was 63.4 (12–166) months.   

Researchers found evidence of PDUS synovitis in 62.4% of patients with RA and 32% of patients with PsA.  These patients were mostly female and were more likely to have been treated with steroids.

Patients with PDUS synovitis had higher serum levels of calprotectin (PDUS-negative [n = 49] 1 μg/ml [0.6–3.7] vs PDUS-positive [n = 43] 2.68 μg/ml [0.22–5.5], p < 0.001), C-reactive protein [CRP] (PDUS-negative [n = 49] 0.07 mg/dl [0.1–0.6] vs PDUS-positive [n = 43] 0.20 mg/dl [0.01–1.4], p = 0.005) and ESR (PDUS-negative [n = 49] 8 mm/h.

Calprotectin was tightly correlated with MSUS scores ( r coefficients >0.50 in all patients with RA). A weaker correlation was found between ESR and joint indices and MSUS scores. Calprotectin also was correlated with the PD scores in patients receiving ADA (ρ = −0.591, P<.001) and ETN (ρ = −0.313, P=.039), but not those treated with IFX.

An area under the curve (AUC) of f 0.826 (95 % CI 0.742–0.910) was generated in accuracy analysis with PDUS synovitis (present or not present) as the reference variable with a cut-off calprotectin level of 1.66 μg/ml (sensitivity 79.1 %, specificity 83.4 %).  This calprotectin level was associated with a positive likelihood ratio of of  2.77 and a negative likelihood ratio of 2.29.  

Using these values,  85% of patients were correctly classified as having PDUS synovitis.

“ROC analysis showed a lower accuracy than calprotectin, with an AUC of 0.721 (95 % CI 0.612–0.829, P =.005) and a cut-off DAS28-CRP value of 1.61 (sensitivity 72 %, specificity 61 %, positive likelihood ratio 1.85, negative likelihood ratio 0.45), and it correctly classified PDUS synovitis in 66.3 % of patients,” the researchers found.

After multivariate regression analysis adjustments, a strong association was found with calprotectin and PDUS synovitis (odds ratio [OR] 4.6, 95 % CI 2.31–9.26, P< .001) after accounting for combined therapy, reduced dose, use of glucocorticoids, disease duration, and presence of autoantibodies or erosive disease.

When analyzing TNFi serum troughs, researchers found that low troughs were were significantly associated with PDUS synovitis (OR 0.67, 95 % CI 0.52–0.85, P< .001),  but that they were associated with low accuracy (AUC <0.5). Calprotectin was inversely related with serum trough levels of  ADA (ρ = −0.461, P= .008) and ETN (ρ = −0.436, P=.005).

“Calprotectin and TNFi serum levels may be considered as sensitive biomarkers of synovial inflammation in RA and PsA patients in remission or with low disease activity being treated with TNFi,” the researchers stated. These biomarkers may help identify which patients have ultrasound active synovitis despite being in clinical remission or deemed to have low disease activity.

Summary and Clinical Applicability

Patients with RA and PsA who also had PDUS-evident synovitis had higher levels of serum calprotectin and lower TNFi troughs, suggesting that these values may help identify patients with PDUS synovitis in clinical remission or low disease activity.

“Calprotectin and drug trough serum levels may help clinicians identify US active synovitis in RA and PsA patients in clinical remission or with low disease activity treated with TNFi,” the researchers concluded. 

Limitations and Disclosures

  • Cross-sectional study design
  • Selection of DAS28 ≤ 3.2 allowed patients with residual tender and swollen joints to be labelled as being in remission
  • Inclusion of patients with long-standing disease on protracted TNFi therapy limited the prognostic utility of calprotectin, TNFi troughs, and PDUS-evidence synovitis in detecting flares or therapeutic response
  • No standardized accounting for concomitant therapy with conventional synthetic DMARDs, corticosteroids, and non-steroidal anti-inflammatory drugs
  • Ultrasound assessment was performed by a single ultrasonographer, such that no comment on inter-observer reliability can be made 

No competing interests were declared by study researchers.


  1. Inciarte-mundo J, Ramirez J, Hernández MV, et al. Calprotectin and TNF trough serum levels identify power Doppler ultrasound synovitis in rheumatoid arthritis and psoriatic arthritis patients in remission or with low disease activity. Arthritis Res Ther. 2016;18(1):160.
  2. Iagnocco A, Finucci A, Ceccarelli F, Perricone C, Iorgoveanu V, Valesini G. Power Doppler ultrasound monitoring of response to anti-tumour necrosis factor alpha treatment in patients with rheumatoid arthritis. Rheumatology (Oxford). 2015;54:1890–6.

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