The urine level of plasma complement fragment Ba in patients with antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) might serve as a biomarker for the surveillance of active renal vasculitis, as it increases at the time of a renal flare due to intrarenal complement activation, according to an article published in Kidney International Reports.

The study measured Ba levels in urine and plasma samples of 60 patients with AAV at multiple time points. Of 60 participants, 21 developed a renal flare, 19 had a nonrenal flare, and 20 were in long-term remission.

The researchers performed ELISA testing and corrected the urine Ba levels for urine creatinine concentration. They modeled the changes in Ba levels using mixed linear-effect models and used a logistic regression model to predict a renal flare using Ba levels at the time of flare versus the nonrenal flare and long-term remission groups.

According to the results, plasma levels of Ba remained stable over time across all groups. However, Ba levels in urine increased during renal flares while remaining stable at nonrenal flares and long-term AAV remission.

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Furthermore, the analysis suggested that urine Ba levels may serve as a predictor of renal flares with an area under the curve of 0.76 (P <.001) and with a cutoff of 12.53 ng/mg urine creatinine concentration. The sensitivity and specificity of Ba urine levels as a biomarker were assessed as 76.2% and 68.4%, respectively.

“There was significant variation in plasma and urine Ba levels between patients at the time of a renal flare, suggesting that the intensity of complement activation may be different between patients,” Almaani and colleagues noted.

“The findings from this study highlight an important caveat of utilizing cross-sectional data for biomarker discovery. As found in this study, a biomarker that demonstrates utility in a cross-sectional analysis may not be useful for longitudinal surveillance.”

The alternative complement pathway contributes to the development of AAV, however, the exact mechanism of its involvement remains unclear.


Almaani S, Song H, Suthanithra M, et al. Urine and plasma complement Ba levels during disease flares in patients with ANCA-associated vasculitis. Kidney Int Rep. Published online August 20, 2023. doi:10.1016/j.ekir.2023.08.017