More severe kidney damage seen in patients with MPA than other types

Most AAV patients in US experience kidney injury, according to 5-year study

Patricia Inacio, PhD avatar

by Patricia Inacio, PhD |

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Most people with ANCA-associated vasculitis (AAV) experience acute or chronic kidney injury, according to a five-year national study in the U.S.

More severe kidney damage is observed in people with the AAV disease type microscopic polyangiitis (MPA) than in those with granulomatosis with polyangiitis (GPA), and less severe symptoms are seen in people with eosinophilic granulomatosis with polyangiitis (EGPA), data show.

“Maintaining a high index of suspicion and a low threshold for kidney biopsy should help ameliorate short and long-term complications,” researchers wrote.

The study, “Antineutrophil Cytoplasmic Antibody-Associated Vasculitis with Active Kidney Involvement in the United States: 2016–2020,” which was published in the journal Glomerular Diseases.

AAV is an autoimmune disorder characterized by inflammation in small blood vessels. The disease is classified into three types — MPA, which is more commonly associated with kidney involvement; GPA, generally linked to a higher relapse rate; and EGPA, the rarest form. When blood vessel inflammation is restricted to the kidneys alone, patients have a form of disease called renal-limited vasculitis.

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AAV can lead to kidney failure

The kidneys, which contain small blood vessels that help filter waste from the body, are especially vulnerable to damage from AAV. In 30% to 50% of patients whose kidneys are affected, the disease progresses into kidney failure within five years.

However, few studies have assessed the characteristics of AAV in patients with active kidney involvement in the U.S., such as hospitalization duration, inpatient costs, AAV subtypes, regional differences, and hospital characteristics.

To address this knowledge gap, researchers at Stanford University School of Medicine analyzed data from the National Inpatient Sample database from 2016 to 2020. They focused their analysis on hospitalized adults with AAV who underwent a kidney biopsy but had no kidney failure before hospital admission.

They identified 1,329 such records per year during the five-year period. In total, this corresponded to 6,645 hospitalizations nationwide, which included 105 patients with EGPA, 1,640 with GPA, and 1,360 with MPA. Most patients, a total of 3,540, were not diagnosed with a specific subtype, likely due to a delay in lab work. These patients were labeled as unspecified vasculitis.

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Compared to GPA and MPA (mean age 63.8 to 68.7 years), EGPA patients were younger (60.5 years). The proportion of women was higher in MPA (57.7%) than in the other subtypes (48.2% GPA and 47.6% EGPA).

Between 60.7% and 71.7% of patients with GPA, MPA, and unspecified vasculitis were insured with Medicare/Medicaid. Also, 32.7% to 36.6% were treated in the South, followed by the West and Midwest, each accounting for 20.4% to 27.7% of patients. The lowest proportion was in the Northeast region, ranging from 15.2% to 17.7%.

Urban teaching hospitals treated 79.9% to 83.5% of patients from these groups, with more than half of patients admitted to hospitals with large beds.

Chronic kidney disease was more common in people with MPA (32.7%) than with GPA (26.8%). The same was seen for diabetes — 29% for MPA vs. 19.5% for GPA — while the opposite was found for obesity, which was 21% in GPA vs. 15.4% in MPA.

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Acute kidney injury most prevalent in MPA patients

Acute kidney injury was detected in over 85.7% of patients across all groups, but the highest prevalence of 94.9% was in MPA patients.

Still among the GPA, MPA, and unspecified vasculitis groups, dialysis was required by 19.6% to 24.6% of patients, and plasma exchange by 10.2% to 20.6%. Sepsis (an extreme response to an infection) was diagnosed in less than 10% (5.5%-9.5%) of cases and 17.4% to 23.2% experienced insufficient oxygen levels, or hypoxia. Mechanical ventilation was required by 4.3% to 5.9% of these patients.

The percentage of patients with chronic pulmonary disease was higher in the EGPA (57.1%) group than in the GPA (22.6%) and MPA (23.5%) groups. In contrast, sepsis, pneumonia, increased acidity in the blood, and the need for catheter and dialysis were less common in EGPA.

Also, no EGPA patient required mechanical ventilation or plasma exchange, a therapeutic approach used to clean the blood by removing and replacing a person’s plasma. Infusion of antibodies, however, was more likely among these patients — 9.5% vs 2.7% (GPA) and 4.4% (MPA).

Over a third of patients (34.2%) were discharged to a rehabilitation facility. In-hospital mortality was relatively low, with five deaths each in the GPA and MPA groups. No significant differences in lengths of hospital stay or inpatient costs were seen between the different AAV subtypes, as well as in hospital bed size, or teaching status.

The highest costs were registered in the West region and the lowest in the Midwest. Hospital stays were the longest in the Northeast and shortest in the Midwest.

“AAV with acute kidney involvement remains a challenging, high-risk condition,” the scientists wrote. “Observational (‘real-world’) studies incorporating longer term outcomes […] and prospective randomized clinical trials are needed to improve outcomes associated with these rare diseases.”