Reference Range of Red Cell Distribution Width‐to‐Albumin Ratio in Healthy US Adults: A Cross‐Sectional Study

The red blood cell distribution width‐to‐albumin ratio (RAR) has been identified as a reliable prognostic marker for all‐cause mortality and various diseases. However, the reference range for RAR across different sexes, age groups, and races remains unknown. This study was conducted to establish age‐, sex‐, and race‐specific reference intervals for the RAR in the general US adult population. A cross‐sectional analysis was performed using seven biennial cycles (2005–2018) of the National Health and Nutrition Examination Survey (NHANES), comprising 22,582 adults aged ≥ 18 years. Pregnant or lactating women and individuals with a history of diabetes mellitus, cardiovascular or cerebrovascular disease, liver disease, thyroid disease, kidney disease, or malignancy were excluded. Age‐, sex‐, and race‐stratified reference intervals (2.5th–97.5th percentiles) for RAR were derived using survey‐weighted methods. The weighted analysis represented more than 141 million US adults. The median RAR was 3.0 %dL/g (IQR: 2.8–3.2), with slightly higher values observed in women compared with men and a modest age‐dependent increase observed. Non‐Hispanic Black individuals were found to have marginally elevated RAR compared with other racial/ethnic groups, along with greater variability. The overall reference interval was determined to be 2.5–4.1 %dL/g. The widest interval was observed among non‐Hispanic Black women aged < 65 years; the narrowest, among Hispanic and non‐Hispanic White men in the same age group. In conclusion, RAR reference intervals showed minimal variation across demographic strata, supporting the potential utility of RAR as a robust biomarker for clinical and research applications.