The study examined the relationship between neutrophil percent albumin ratio (NPAR) and sarcopenia in adults with arthritis, including osteoarthritis, rheumatoid arthritis, and other types of arthritis, based on data from the NHANES survey (1999–2006, 2011–2018). The results showed that a higher NPAR value is associated with a higher prevalence of sarcopenia in patients with arthritis; specifically, each one-unit increase in NPAR increased the odds of sarcopenia by 22% (OR 1.22, 95% CI 1.09–1.36). In rheumatoid arthritis and other types of arthritis, this correlation was significant (OR 1.36 and 1.37), whereas in osteoarthritis it was not significant. NPAR as a composite indicator had a better diagnostic value (AUC 0.587) compared to the individual indicators of neutrophils (AUC 0.571) and albumin (AUC 0.549). The study confirms that NPAR may be a useful and affordable marker to assess the risk of sarcopenia in patients with arthritis.