Inflammation in kidneys raises the risk of them failing in AAV patients
Biopsies collected at diagnosis can help predict kidney failure, study says
People with ANCA-associated vasculitis (AAV) that affects their kidneys are at a significantly increased risk of kidney failure if they show a high proportion of inflamed glomeruli (the organ’s filtering units) on biopsies collected at diagnosis, a study has found.
Severe AAV can lead to kidney failure
AAV is characterized by inflammation in the body’s small blood vessels, which commonly causes damage to the kidneys. Serious cases can lead to kidney failure or end-stage kidney disease (ESKD), where the kidneys aren’t able to function adequately without regular medical intervention.
“To date, several baseline risk factors for the progression to ESKD in patients with AAV have been reported including age, serum [blood] creatinine, estimated glomerular filtration rate (eGFR), blood pressure, [and] the proportion of abnormal glomeruli, tubular atrophy, interstitial fibrosis on kidney biopsy,” the researchers wrote.
Blood creatinine is a marker of kidney damage, tubular atrophy refers to damage in the kidney’s tubules, and interstitial fibrosis refers to scarring of the tissues surrounding cells in an organ.
To assess whether tissue damage features on kidney biopsy could also predict progression to kidney failure in this patient population, a team of researchers in Korea analyzed data from 113 people with AAV-related kidney damage confirmed by a biopsy who were treated at their center.
Patients’ median age at diagnosis was 59 years, and about one-third of them (33.65) were male. Over a median follow-up time of more than three years, 44.2% of the patients developed kidney failure.
The researchers first divided the patients into four groups based on patterns of inflammation and scarring visible on kidney biopsies. The four categories — referred to as focal, crescentic, mixed, and sclerotic classes — were originally defined in a 2010.
The proportion of patients in the sclerotic class (which is generally considered the most severe of the four classes) was significantly higher in the group with kidney failure than among patients who didn’t develop ESKD (35.7% vs. 22.9%).
Statistical analyses showed patients with a biopsy in this severe class had a significantly reduced chance of living without ESKD compared with those in the other three classes.
“When compared between the sclerotic class and the remaining three classes … patients in the sclerotic class exhibited a significantly reduced cumulative [ESKD-free] survival rate,” the researchers wrote.
The researchers also looked at scores for three distinct types of kidney damage that can be visualized on biopsy: interstitial fibrosis, tubular atrophy, and global glomerulitis, or the presence of inflammation in nearly all glomeruli capillaries.
In statistical models adjusted for several potential influencing factors, high global glomerulitis scores were found to be independently and significantly associated with an increased risk of kidney failure, by about threefold.
Patients with more interstitial fibrosis or tubular atrophy also generally were more likely to get ESKD, but these links failed to reach statistical significance in the adjusted statistical models.
Global glomerulitis more powerful at predicting end-stage kidney disease
“Notably, global glomerulitis was more powerful than interstitial fibrosis and tubular atrophy in predicting ESKD,” the researchers wrote.
The statistical models also showed that higher blood levels of two kidney damage markers — urea nitrogen and creatinine — at diagnosis were independently associated with a significantly higher risk of developing kidney failure.
“Since both [blood urea nitrogen] and [blood] creatinine are well-known clinical risk factors for ESKD occurrence … it was not unexpected that they were independent predictors of ESKD,” the researchers wrote.
These findings suggest patients with risk factors such as global glomerulitis and sclerotic class may benefit from more aggressive early treatment to prevent kidney failure.
The researchers noted, however, that this study was limited to patients treated at a single center, so further research is needed to validate and expand on the results.