HP and anemia (phenotype): In addition, we performed a series of analyses, including restricting the range of RAR to limit inter-queue overlap, excluding subjects with clinical anemia, conducting sensitivity analyses by adjusting spline function parameters and handling extreme values, as well as subgroup analyses.<h4>Results</h4>In the main adult dataset of NHANES 1999-2000, RCS regression analysis revealed a significant nonlinear association between RAR and Hp seropositivity rate (overall test <i>p</i> < 0.001; nonlinear test <i>p</i> < 0.001), with the inflection point at RAR = 2.85.