Value in testing kidney function soon after AAV diagnosis: Study

Reassessment of kidney prognosis helps predict risk of renal failure

Patricia Inacio, PhD avatar

by Patricia Inacio, PhD |

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In people with ANCA-associated vasculitis (AAV), evaluating kidney function by a test known as the estimated glomerular filtration rate within six months after their diagnosis helps assess their risk of kidney failure, a study shows.

The study, “Adding 6-month parameters for the prediction of kidney prognosis in ANCA-associated glomerulonephritis,” was published in the Clinical Kidney Journal.

AAV comprises a group of diseases in which autoantibodies (called anti-neutrophil cytoplasmic antibodies, or ANCAs) overly activate cells called neutrophils, resulting in small blood vessel inflammation. This overactivity often leads to glomerulonephritis, a condition in which inflammation affects the tiny filters, called glomeruli, inside the kidneys.

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AAV patients at risk for kidney failure, end-stage kidney disease

Despite treatment with immunosuppressants, AAV may lead to kidney failure and end-stage kidney disease (ESKD). Therefore, early risk indicators for progression to ESKD is paramount to select the best course of treatment.

In the study, researchers in France assessed whether measuring kidney function six months after AAV diagnosis could help identify patients at risk of ESKD. For that purpose, they analyzed data from adults with AAV-glomerulonephritis diagnosed at several centers in France.

In total, 241 patients with a median age of 67 years were analyzed. The main goal was the time to reach ESKD, which was defined by the need for kidney replacement therapy for at least three months or the need for a kidney transplant.

The scientists first analyzed the whole group, and then a group without early ESKD (here called WEE), meaning no kidney failure during the first six months of follow-up.

Of the 241 patients analyzed, most were in the WEE group (221 patients, 62% men) and 150 patients (71%) were positive for ANCAs targeting myeloperoxidase.

At diagnosis, the WEE group had a median of 15 on the Birmingham Vasculitis Activity Score, a measure of disease activity where a higher score indicates more severe disease.

The group’s median estimated glomerular filtration rate (eGFR) was 23 mL/min, and they had high levels of protein in their urine (median 1.2 g/g). A total of 193 patients (91%) also had blood in their urine. Of note, eGFR measures how well the kidneys’ glomeruli are filtering. In general, higher values indicate better kidney function.

Patients were followed for a median of 61 months (about 5 years), during which they received treatment with corticosteroids in combination with the immunosuppressant cyclophosphamide (72%) or rituximab (22%).

Within 30 days of diagnosis, 25 patients (11%) required a kidney replacement therapy, but none developed ESKD. By six months, they had lower urine protein levels and higher eGFR rates.

During follow-up, 42 patients (19%) reached ESKD, 55 (25%) died and 71 (33%) experienced a relapse, including 45 (63%) with kidney involvement.

The researchers then compared the predictive value of eGFR for ESKD with current parameters used in the clinic. These included the Berden classification and the renal risk score.

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Protein levels in urine, eGFR strong predictors of ESKD

In total, 102 patients had sufficient data. Across three different measures — C-index, area under the curve, and the Brier score — eGFR at diagnosis was better than the renal risk score and the Berden classification at predicting the risk of ESKD.

After six months of follow-up, data from 93 patients from the WEE group once again showed eGFR was the best predictor. Also at six months, protein levels in urine and eGFR were strong predictors of ESKD in the WEE group.

Results further showed, among the markers tested, persistent high protein levels at six months was the only one that improved ESKD prediction.

Overall, these findings suggest that within six months of AAV diagnosis, assessing “kidney function at this time remains the most reliable for predicting kidney outcome,” the researchers concluded. “This work suggests the benefit of the reassessment of the kidney prognosis 6 months after AAV-[glomerulonephritis] diagnosis.”