Background and objective: Measuring Takayasu (TAK) disease activity remains a difficult task. The aims of this study were to identify biomarkers reflecting disease activity in TAK, to analyze the effects of treatment, to compare the findings of TAK with Giant Cell Arteritis (GCA) and to assess age-related differences.

Methods: Biomarkers in sera of 26 TAK patients (median age: 33 years) were analyzed and compared with sera of 18 GCA patients (median age: 72 years), meeting the respective 1990 ACR criteria, as well as with sera of age-matched Healthy Controls (HC). In a screening phase, sera levels of 48 biomarkers were quantified using Luminex technology. Biomarkers showing differences between groups and subgroups were confirmed by ELISA. Disease activity was scored using the EULAR criteria of 2018. Additionally, arterial wall signals in MRI were graded from 0 (normal) to 3 (intense late enhancement).

Results: 7/26 TAK patients showed active disease. MRI signals of 11/26 TAK patients indicated vessel wall inflammation. Serum levels of YKL-40 were elevated in TAK patients compared to HC. YKL-40 as well as sIL-2R and CD163 were lower in TAK patients compared to GCA patients; YKL-40 levels were elevated in GCA compared to HC. None of the molecules were significantly associated with clinical disease activity, neither with Magnetic Resonance Angiography (MRA) signal intensity. Analysis of HC showed a significant age correlation of YKL-40, CD163 and MMP-3, and an inverse correlation for Pentraxin-3.

Conclusions: YKL-40 reliably distinguished between TAK and healthy controls. Biomarkers in active GCA were higher compared to TAK. Interpretation of serological markers must consider age-related differences.