The presence of urinary isomorphic red blood cells (RBCs) at diagnosis may predict poor renal outcomes and severe clinical manifestations in patients with antineutrophil cytoplasm antibody (ANCA)-associated vasculitis (AAV) marked by antibodies to myeloperoxidase, a study published in the Journal of Nephrology suggests.

In this retrospective cohort study, the researchers analyzed clinical, biological, and pathological data of 191 patients with AAV with hematuria. They divided all patients into 2 groups based on the prevalence of isomorphic or dysmorphic RBCs on urinary sediment analysis.

The patients were followed up for a median of 25 months. The main outcome events included AAV disease progression to end-stage kidney disease and death.

Moreover, the researchers used univariate and multivariate Cox regression analysis to evaluate end-stage kidney disease risk factors.

Read more about AAV testing

According to the results, 115 patients had at least 70% of isomorphic RBCs in their urine and 76 patients had less than 30%.

The isomorphic RBC group had a significantly lower estimated glomerular filtration rate in comparison with the dysmorphic RBC group, as well as higher rates of glomerular basement membrane fracture as evidenced by kidney biopsy.

Moreover, patients in the isomorphic RBC group had a higher Birmingham Vasculitis Activity Score and more often required plasma exchange at diagnosis compared with those in the dysmorphic RBC group.

The researchers also found that patients with urinary isomorphic RBCs developed end-stage kidney disease more often than those with dysmorphic RBCs, although these findings could not be confirmed by multivariate Cox analysis.

Read more about AAV prognosis

Last, end-stage kidney disease-free survival was lower in the urinary isomorphic RBC group and the risk of death was greater when compared with the dysmorphic RBC group.

“Kidney involvement is the most important predictor of mortality in AAV. Abnormally increased levels of serum creatinine and proteinuria at diagnosis are associated with renal outcome and patient survival. However, the implication of hematuria for predicting the renal outcome in AAV is controversial,” Wang and colleagues explained.

Hematuria, commonly seen in patients with myeloperoxidase-associated AAV, may originate from any part of the urinary system. However, the exact mechanism of RBC deposition in the urine of those with kidney disease has not been clarified.


Wang F, Jin Y, Zhou F, et al. Urinary isomorphic red blood cells for the prediction of disease severity and renal outcomes in MPO-ANCA-associated vasculitis: a retrospective cohort study. J Nephrol. Published online July 3, 2023. doi:10.1007/s40620-023-01663-3