Eosinophils linked to severe disease in ANCA-associated vasculitis types

Counting the white blood cells may help predict survival with MPA, GPA

Margarida Maia, PhD avatar

by Margarida Maia, PhD |

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A dropper is seen squirting blood alongside four half-filled vials of blood.

A higher eosinophil count at diagnosis is linked to more severe disease activity in people with microscopic polyangiitis (MPA) or granulomatosis with polyangiitis (GPA), the two most common types of ANCA-associated vasculitis (AAV), a study suggests.

Counting eosinophils, white blood cells that usually release enzymes and other molecules in response to infection and allergens, may also help predict the chances of survival during follow-up and inform on the disease’s prognosis.

The study, “Clinical implications of peripheral eosinophil count at diagnosis in patients newly diagnosed with microscopic polyangiitis and granulomatosis with polyangiitis,” was published in Arthritis Research & Therapy.

AAV occurs when white blood cells called neutrophils go haywire and cause small blood vessels to become inflamed. The swelling can make it hard for blood to flow through the vessels, damaging the organs they supply. Unlike in eosinophilic granulomatosis with polyangiitis, a type of AAV defined by an increase in eosinophils, this type of white blood cell isn’t believed to play a role in other types of AAV such as MPA and GPA.

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Eosinophil count at diagnosis

Researchers in Korea examined how the number of eosinophils in the blood at diagnosis may help estimate the severity of AAV and predict the likelihood of survival with MPA and GPA. The study included 224 adults, median age 62, who had received a diagnosis of AAV at a Korean tertiary university hospital; 152 (67.9%) had MPA and 72 (32.1%) had GPA. Over a median 47.8 months (about four years) of follow-up, 36 patients died.

At diagnosis, the median eosinophil count was 190 cells per cubic millimeter. The higher the eosinophil count, the higher the Birmingham Vasculitis Activity Score (BVAS), a measure of disease activity where a higher score indicates more severe disease.

The eosinophil count was linked to the Five Factor Score, a tool used to predict outcomes. It also was linked to the erythrocyte sedimentation rate and the level of C-reactive protein, two measures of inflammation.

While “an increase in peripheral [blood] eosinophil count in patients newly diagnosed with MPA and GPA might be negligible,” the findings suggest a higher eosinophil count may have “clinical implications,” the researchers wrote.

When they received their diagnosis, people with MPA had significantly more eosinophils than people with GPA (200 vs. 145 cells per cubic millimeter). Those with symptoms in the heart or kidneys also had a higher eosinophil count than those without these symptoms.

Moreover, those who died had a higher eosinophil count than those who survived (310 vs. 170 cells per cubic millimeter). Those with a count of 175 eosinophils per cubic millimeter or higher were found to have a lower cumulative survival rate during follow-up than those with counts below that cutoff.

The findings suggest eosinophil count at diagnosis may provide insights into the severity of AAV and contribute to predicting death by any cause in people with MPA or GPA. A study of more patients over time may yield better information on the “clinical implications of peripheral eosinophil count at diagnosis in patients newly diagnosed with MPA and GPA,” the researchers said.