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.