The Association of Low Hemoglobin Levels with IgA Nephropathy Progression: A Two-Center Cohort Study of 1,828 Cases

Abstract

Aim: To investigate the relationship between hemoglobin levels and the progression of IgA nephropathy (IgAN). Methods: In a two-center cohort of 1,828 cases with biopsy-proven IgAN, we examined the association of hemoglobin levels with the primary outcome of a composite of all-cause mortality or kidney failure defined as a 40% decline in eGFR, or ESKD (defined as eGFR <15 mL/min/1.73 m² or need for kidney replacement therapy including hemodialysis, peritoneal dialysis, or kidney transplantation), or the outcome of kidney failure, assessed using Cox and logistic regression models, respectively, with adjustment for confounders. Results: At baseline, mean age, eGFR, and hemoglobin levels were 33.75 ± 11.03 years, 99.70 ± 30.40 mL/min/1.73 m², and 123.47 ± 18.36 g/L, respectively. During a median of approximately 7-year follow-up, 183 cases reached the composite outcome. After adjustment for demographic and IgAN-specific covariates and treatments, a lower quartile of hemoglobin was nonlinearly associated with an increased risk of the primary outcome or kidney failure in the Cox proportional hazards models (primary outcome: HR for quartile 3 vs. 4, 1.37; 95% CI, 0.83–2.25; HR for quartile 2 vs. 4, 1.18; 95% CI, 0.68–2.07; HR for quartile 1 vs. 4, 1.91; 95% CI, 1.15–3.17; kidney failure: HR for quartile 3 vs. 4, 1.39; 95% CI, 0.84–2.31; HR for quartile 2 vs. 4, 1.20; 95% CI, 0.68–2.11; HR for quartile 1 vs. 4, 1.83; 95% CI, 1.09–3.07) in the fully adjusted model. Then, hemoglobin levels were transformed to a binary variable for fitting the model according to the criteria for anemia of 110 g/L in the women and 120 g/L in men in China. The participants in the anemia group had an increased risk of developing outcomes compared with the nonanemia group in both genders (primary outcome: male: HR, 1.64; 95% CI, 1.01–2.68; female: HR, 1.68; 95% CI, 1.02–2.76; kidney failure: male: HR, 1.60; 95% CI, 0.97–2.64; female: HR, 1.58; 95% CI, 0.95–2.61) in the fully adjusted model. Conclusions: A low level of hemoglobin was nonlinearly associated with IgAN progression. The anemic IgAN patients presented a higher risk of developing poor outcomes compared with the nonanemic patients.