Limited Clinical Utility of Serum Prealbumin for Assessing DXA-Derived Lean Mass After Roux-en-Y Gastric Bypass: Longitudinal and Long-Term Cross-Sectional Analyses

Background/Objectives: Despite recognized physiological limitations, serum prealbumin continues to be measured during nutritional follow-up after bariatric surgery, and low concentrations may be interpreted as indicating inadequate lean-mass preservation. We aimed to evaluate the clinical utility of serum prealbumin for identifying disproportionate DXA-derived lean mass loss during the first three years after Roux-en-Y gastric bypass (RYGB) and to examine its association with DXA-derived lean-mass measurements at long-term follow-up. Methods: In a longitudinal cohort of 178 adults, serum prealbumin and dual-energy X-ray absorptiometry (DXA)-derived body composition were assessed preoperatively, at 6 months, 1 year, and 3 years after surgery. Disproportionate lean mass loss was defined as lean mass accounting for >25% of total body weight lost. A complementary cross-sectional analysis examined associations between prealbumin and body composition in 310 participants assessed at a median of 8.8 years after RYGB. Results: Prealbumin decreased from an estimated 0.260 g/L preoperatively to 0.203 g/L at 6 months and partially recovered thereafter, while absolute lean mass continued to decline through 3 years. Prealbumin showed poor discrimination of disproportionate lean mass loss, with AUCs of 0.36, 0.28, and 0.48 at 6 months, 1 year, and 3 years, respectively, although estimates were imprecise because of the small number of participants meeting the criterion. The <0.20 g/L prealbumin threshold showed low sensitivity of 12–27%. Lower prealbumin concentrations were not significantly associated with the percentage of preoperative lean mass lost at any time point. In the long-term analysis, prealbumin was not meaningfully associated with DXA-derived lean mass measures after adjustment for sex, age, and time since surgery. Conclusions: Serum prealbumin showed limited discriminatory performance for identifying disproportionate DXA-derived lean mass loss during the first three years after RYGB, although estimates were imprecise because of the small number of events. In the long-term cross-sectional cohort, associations with DXA-derived lean-mass measurements were weak. These findings do not support the use of serum prealbumin as a surrogate marker of DXA-derived lean mass preservation after RYGB.