Serum immunoglobulin A levels: Diagnostic utility in alcoholic liver disease and association with liver fibrosis in steatotic liver disease.

The relationship between immunoglobulin A (IgA) levels and chronic liver disease remains poorly understood. The present study evaluated the clinical significance of IgA in 478 new patients who visited the Outpatient Clinic of Nagasaki Harbor Medical Center (Nagasaki, Japan). Serum IgA levels in comparison to liver stiffness (LS), as measured using a FibroScan device, were evaluated in 358 patients. Furthermore, in 270 patients, the associations between serum IgA levels and body composition were analyzed using computed tomography. The IgA levels of patients in the groups with Child-Pugh classification B and C (CPGBC), alcoholic liver disease (ALD), steatotic liver disease (SLD) or diabetes were higher than the IgA levels of patients in the groups with CPGA, non-ALD, non-SLD or no diabetes, respectively. Logistic regression analysis showed that CPGBC, ALD, high IgG (>1,700 mg/dl), high macrophage galactose-specific lectin-2 binding protein glycosylation isomer (M2BPGi) (>1 cut-off index) and diabetes were contributing factors for high serum IgA level (>410 mg/dl). The ratio of IgA level divided by IgG level was highest in patients with ALD, followed by those with metabolic dysfunction-associated SLD (MASLD) and non-SLD. In SLD, IgA level was associated more with LS than M2BPGi and fibrosis-4 (FIB-4) in multiple regression analysis. In the receiver operating characteristic analysis, IgA level, M2BPG, and FIB-4 had similar area under the curve values for discriminating high LS (>8 kPa) from low LS (≤8 kPa) in SLD. IgA levels were also associated with visceral fat, and this association was only found in women. In conclusion, elevated IgA is an indicator of liver fibrosis that also reflects the presence of diabetes and an increased visceral fat level. Therefore, IgA is considered a useful marker of liver disease severity in the current era of increased SLD.