ANCA blood tests may help detect kidney involvement: Study
Test not as accurate as kidney biopsy, but less invasive
Blood tests that look for the anti-neutrophil cytoplasmic autoantibodies (ANCAs) that cause ANCA-associated vasculitis (AAV) may help identify patients with kidney involvement, a study shows.
Still, ANCA testing was not as accurate for this purpose as a kidney biopsy, wherein a small piece of kidney tissue is collected for analysis.
“While [blood] ANCA measurement may not be able to replace [kidney] biopsy, measurement and reporting of [ANCA levels] will assist in the decision to start treatment early for patients with organ or life-threatening diseases,” the researchers wrote in the study, “Diagnostic accuracy of ANCA serology in ANCA-associated vasculitis with renal involvement,” in the Internal Medicine Journal.
ANCA-associated vasculitis is a group of autoimmune diseases marked by inflammation and damage to small blood vessels, affecting the function of tissues and organs, including the kidneys. Kidney involvement in AAV manifests as pauci-immune glomerulonephritis, a type of inflammation of their filtering units that doesn’t present with deposits of certain immune proteins. A kidney biopsy is the gold standard for detecting pauci-immune glomerulonephritis and, while it’s highly accurate for detecting disease, it’s an invasive procedure and “may not be readily accessible in peripheral hospitals,” the researchers wrote.
For this reason, identifying a less invasive way to detect AAV-related pauci-immune glomerulonephritis is needed.
ANCA blood tests and kidney involvement
Most AAV cases are associated with self-reactive antibodies called ANCAs being produced that drive the damaging inflammation in blood vessels. ANCA testing is reasonably accurate for diagnosing whole-body AAV, but no study had evaluated its diagnostic potential for AAV-related kidney involvement, leading researchers in Australia to analyze data from 507 adults who’d undergone a kidney biopsy and had their ANCA levels measured.
Forty-one people (8.1%) had biopsy-confirmed pauci-immune glomerulonephritis and all but one tested positive for ANCAs, meaning they had higher than normal levels.
The researchers then constructed statistical models to look at various cutoffs for ANCA-based detection of pauci-immune glomerulonephritis. They found that ANCA detection at any higher than normal level could accurately identify 97.6% of patients with pauci-immune glomerulonephritis and correctly rule out 71.2% of those without the condition. Using an increasing ANCA cutoff was associated with a lower ability to correctly identify patients with kidney involvement, but a higher ability to correctly rule out those without it.
A model adjusted for sex and the presence of acute kidney injury and blood in urine showed that each incremental rise in ANCAs was significantly associated with a twofold higher chance of having pauci-immune glomerulonephritis.
ANCA levels against proteinase 3 (PR3) or myeloperoxidase (MPO), the two most common targets of AAV-driving antibodies, were significantly higher among those with pauci-immune glomerulonephritis than those with an alternative diagnosis. And those with higher ANCA levels were significantly more likely to have ANCAs specifically targeting either PR3 or MPO than those with lower levels. Moreover, combining ANCA positivity with levels of ANCAs against either target further increased the diagnostic accuracy for AAV-related kidney involvement.
ANCA testing may help identify pauci-immune glomerulonephritis in patients who show signs of kidney disease, especially if a kidney biopsy isn’t feasible, data show.
“ANCA [levels], along with MPO and PR3 levels, are highly predictive of pauci-immune [glomerulonephritis] in the appropriate context,” the scientists wrote. “However, when clinically suitable, a biopsy remains the gold standard test that provides additional information, including measures of disease activity and chronicity, which may assist in determining the intensity of immunosuppressive treatment.”
About the Author
