Hemoglobin Levels Predict Course of AAV-Related Kidney Disease

Low blood levels link with need for intensive care in hospitalized adults

Steve Bryson, PhD avatar

by Steve Bryson, PhD |

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Intensive care stays are more likely if oxygen-carrying hemoglobin levels are low at hospital admission in adults with kidney disease caused by ANCA-associated vasculitis (AAV), an analysis of medical records found.

Severe kidney injury was the primary reason for intensive care unit (ICU) admission in these patients and associated with kidney replacement therapy (KRT), a life-supporting procedure replacing the kidneys’ role in removing waste products and excess fluid from the blood.

These findings help in understanding the role of hemoglobin in AAV-related kidney disease, its scientists noted.

The study, “Low levels of hemoglobin associate with critical illness and predict disease course in patients with ANCA-associated renal vasculitis,” was published in the journal Nature Scientific Reports.

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A person drinks a glass of water, which is important for the proper function of the kidneys, highlighted here.

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Kidney involvement found in up to half of AAV patients

Kidney, or renal, involvement occurs in up to 50% of AAV patients at disease onset and is a severe AAV complication resulting in acute kidney injury that progresses to chronic kidney disease. While current treatments can lead to disease remission in up to 80% of cases, some patients fail to respond and may need kidney-related ICU support.

However, data on AAV patients admitted to the ICU due to kidney involvement as the main AAV complication are limited, with most studies focused on long-term kidney and overall outcomes. Particularly, information on critical illness during the initial course of the disease is scarce.

Researchers at the University Medical Center Göttingen, in Germany, examined the medical records of 53 patients to identify predictors of critical illness in those with AAV-associated renal vasculitis.

Participants were 30 men and 23 women, with a median age at diagnosis of 65 years (ranging from 54.5 to 74.5). Approximately half (49.1%) were diagnosed with microscopic polyangiitis (MPA) and the remainder with granulomatosis with polyangiitis (GPA), both AAV subtypes, with a new diagnosis of AAV-related kidney involvement in the majority of cases.

KRT was required in 16 patients (30.2%) within 30 days of hospital admission, but none needed mechanical ventilation for respiratory failure. ICU supportive care was given to 24 patients (45.3%), with a median ICU stay of four days and an ICU mortality rate of 12.5%.

The median four-day ICU stay for kidney involvement was shorter than most previous reports focusing on critical illness due to AAV-related lung involvement, the team noted.

Critical illness due to severe AAV-related kidney disease was confirmed, and all 53 individuals underwent diagnostic kidney biopsies. Most patients (83%) also had disease manifestations outside the kidneys, including in the lungs, sinuses, joints, ears, eyes, nerves, and skin.

Compared with those who did not require ICU, patients who needed an ICU stay were similar in age, gender, AAV subtypes, relapsing disease, disease activity, or additional involvement.

As reflected by KRT within 30 days of admission, severe kidney injury risk was significantly higher in patients who required ICU than in those who did not. In-hospital length of stay was also significantly longer in patients requiring ICU. The use of AAV therapies, such as steroids and plasma exchange, given to lower the levels of disease-causing antibodies in the bloodstream, was significantly more frequent in the ICU group.

Researchers concluded that severe kidney injury was the primary reason for ICU admission and associated with KRT during the disease’s course. Critical illness due to kidney failure drove this group’s increased use of plasma exchange and steroid pulse treatments.

Low hemoglobin levels independently linked to ICU admission

Next, the team examined tests at hospital admission to identify factors associated with an eventual ICU stay.

Markers of kidney injury, including blood creatinine levels, eGFR decline, and urinary protein levels, were markedly higher in the ICU group, as were the levels of C-reactive protein, an inflammation marker, and gamma-glutamyl transferase, a liver damage indicator.

Hemoglobin, the protein that carries oxygen in red blood cells, and hematocrit — the proportion of red blood cells in the bloodstream — were both significantly lower in those admitted to the ICU.

Statistical analysis revealed that low hemoglobin levels were independently associated with an eventual ICU admission. Further calculations significantly linked a hemoglobin level below 9.8 grams per deciliter of blood (g/dL) with ICU admission. For reference, normal hemoglobin levels range from 14.0–17.5 g/dL for men, and 12.3–15.3 g/dL for women.

A level of hemoglobin under 9.8 g/dL at admission also associated with a prolonged in-hospital stay compared with hemoglobin levels above this cutoff (median of 25 vs. 12.5 days). Notably, low hemoglobin was linked to a more prolonged ICU stay in the ICU group (median of six vs. three days), but not for the total in-hospital stay in the ICU or non-ICU group.

“These results confirm that low hemoglobin levels at admission associated with critical illness and requirement of ICU supportive care, but also predicted disease course specifically in this subgroup of severe ANCA-associated renal vasculitis,” the scientists wrote.

“Since identification of patients at risk for a more severe disease course is of relevance for treating intensivists, these findings could further improve our current understanding for the role of anemia in ANCA-associated renal vasculitis as it has already been observed in other autoimmune and inflammatory diseases,” they added.