Albuminuria and hematologic profiles across eGFR categories in U.S. adults: NHANES 2001-2018 with detailed iron-biomarker analysis.

BACKGROUND

Albuminuria and estimated glomerular filtration rate (eGFR) are complementary dimensions of kidney disease, but the hematologic phenotype of albuminuria beyond reduced filtration is incompletely defined.

METHODS

We analyzed adults aged ≥20 years in nine National Health and Nutrition Examination Survey (NHANES) cycles (2001-2018). The primary outcome was hemoglobin; secondary outcomes were anemia, red-cell indices, and serum iron. UACR was modeled per doubling and by KDIGO A1-A3 categories using survey-weighted models adjusted for eGFR and clinical covariates. Ferritin, transferrin saturation (TSAT), iron-binding measures, and soluble transferrin receptor (sTfR) were examined in 2017-2018.

RESULTS

Among 42,634 participants, 40,705 entered the primary model. The prespecified primary hypothesis was not supported: UACR was not significantly associated with mean hemoglobin (beta per doubling, -0.008 g/dL; 95% confidence interval [CI], -0.020 to 0.004). UACR was associated with secondary anemia (odds ratio [OR] per doubling, 1.112; 95% CI, 1.078-1.147; A2 vs A1, OR 1.332; A3 vs A1, OR 1.855). RDW, MCV, MCH, and serum iron differences were small; sTfR showed a small exploratory association. Ferritin- and TSAT-based phenotypes were not significantly associated with UACR.

CONCLUSIONS

The prespecified mean-hemoglobin hypothesis was not supported. Higher UACR was associated with threshold-defined anemia as a secondary outcome, while small red-cell and iron-marker differences did not establish conventional absolute iron deficiency or imply changes in anemia management.