Blood sulfatide count at AAV diagnosis may predict kidney failure
Predictive potential of fatty molecule levels independent of kidney involvement
People with ANCA-associated vasculitis (AAV) patients whoo have low blood levels of sulfatides, a type of fatty molecule, are significantly more likely to have future kidney failure, a single-center study in South Korea indicates.
The predictive potential of blood sulfatide levels was independent of direct associations with kidney involvement at diagnosis, as assessed with a standard measure of AAV activity in the kidneys and other organ systems, or blood creatinine levels, a marker of kidney function.
“This study highlighted the clinical usefulness of measuring [blood] sulfatide levels at the time of diagnosis as a biomarker to predict [kidney failure] progression in patients with AAV regardless of kidney involvement at diagnosis,” the researchers wrote.
The study, “Prediction potential of serum sulfatide levels at diagnosis for end-stage kidney disease progression in ANCA-associated vasculitis,” was published in Medicine.
AAV is typically caused by ANCAs, self-reactive antibodies that bind to and over-activate neutrophils, a type of immune cell. This leads to inflammation of the small blood vessels, including those in the kidneys. Patients with kidney involvement may see progression to kidney failure, or end-stage kidney disease (ESKD), where the organs can no longer function properly such that kidney replacement treatments are needed.
Sulfatides are fatty molecules in several tissues and organs, including the kidneys, that are involved in the inflammatory pathway of blood vessels. Research suggests low blood sulfatide levels are associated with worse AAV-related kidney disease, but it isn’t known if sulfatide levels at diagnosis can predict poor outcomes, such as kidney failure and death.
Low sulfatide levels and kidney failure
Here, researchers in South Korea analyzed data from 67 AAV patients treated at a single Korean university hospital and followed up for at least six months. The patients were a mean age of 61 and more than half were women (59.7%). The most common type of AAV was microscopic polyangiitis (MPA; 50.7%), followed by granulomatosis with polyangiitis (31.3%), and eosinophilic granulomatosis with polyangiitis (17.9%).
More than half the patients (56.7%) had ANCAs that target the myeloperoxidase enzyme (MPO) while 16.4% had ANCAs against the proteinase 3 enzyme (PR3). Both MPO and PR3 are found in neutrophils.
AAV activity was measured at diagnosis using the Birmingham Vasculitis Activity Score (BVAS), a standard measure of blood vessel inflammation in nine systems and organs, where higher values indicate more disease activity. The five-factor score (FFS) was used to assess disease prognosis, with higher scores indicating worse disease and an increased risk of death.
Based on BVAS at diagnosis, AAV most commonly affected the lungs (61.2% of patients), followed by ear, nose, and throat (49.3%), and the kidneys (43.3%). Nearly all the patients (98.5%) were treated with glucocorticoids, followed by the immunosuppressants azathioprine (68.7%) and cyclophosphamide (62.7%).
Ten patients (14.9%) progressed to kidney failure and four (6%) died over a median of 29 months, or nearly 2.5 years, of follow-up.
The median blood level of sulfatide at diagnosis was 306.1 picograms per milliliter (pg/mL). Sulfatide levels were significantly associated with higher scores on BVAS-kidney items, higher FFS, higher erythrocyte sedimentation rate, which is a marker of inflammation, and lower estimated glomerular filtrate rate (a measure of kidney function) at diagnosis.
Moreover, at diagnosis, lower sulfatide levels were associated with the presence of anti-MPO ANCAs and kidney involvement. No significant differences in levels were seen between men and women, or were associated with anti-PR3 ANCAs.
Blood sulfatide levels of 332.5 pg/mL at diagnosis were the optimal cutoff value to predict kidney failure during follow-up, further statistical analysis indicated. Specifically, 22.7% of patients with sulfatide levels of up to 332.5 pg/mL progressed to kidney failure compared with none of those with higher levels. Also, those with low sulfatide showed lower kidney failure-free survival rates.
“The present study provided valuable information on the clinical utility of [blood] sulfatide levels at diagnosis to measure [end-stage kidney disease] progression by identifying patients with AAV vulnerable to the occurrence of [kidney] dysfunction during follow-up,” the researchers wrote.
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