ALB and rheumatoid arthritis: Accordingly, we further tested the MR results of serum ALB and RA for heterogeneity and horizontal multiple validity, which showed that the causal relationship of ALB to RA was very robust without heterogeneity and horizontal validity, and the causal relationship of RA to ALB by the MR-PRESSO method suggested that there was heterogeneity, but the results were corrected to show that a significant negative correlation still existed (Table 4).