Introduction &amp; Objective: Muscle and bone can interact with each other, but the effect of muscle on osteoporosis treatment is not clear. This study aims to study the correlation between 24 h Ucr (24-hour urinary creatinine excretion, an indicator of muscle mass) and the change of lumbar spine bone mineral density (BMD) after treatment with Zoledronic Acid (ZOL), and develop an effective model for BMD improvement prediction. Patients and Methods: A total of 169 adults with primary osteoporosis receiving ZOL (5 mg once year) were included. BMD was measured at baseline and 1 year after treatment. BMD improvement was defined as a percentage increase greater than the minimum BMD change (2.78%). Results: 24 h Ucr was negatively correlated with 1 year lumbar BMD changes (r = -0.208, p = 0.007) after treatment with ZOL. Binary logistic regression analysis showed that after adjusting for sex, age, height, weight, diabetes mellitus, baseline lumbar BMD and serum creatinine, 24 h Ucr was an independent predictor of improvement in lumbar BMD after 1 year of ZOL treatment (odds ratio 0.580, 95% confidence interval 0.456 - 0.738, p &amp;lt; 0.001). A new model logit (P) ( -1.321 + 1.864 × gender (female = 1, male = 2) + 9.8 × height (m) - 1.038 × T2DM (yes = 1, no = 0) - 0.582 × 24h Ucr (mmol/d) + 0.061 × creatinine (umol/L) - 16.958 × lumbar BMD (baseline) (g/cm2)) constructed by binary logistic regression analysis with backward selection predicted that the area under the curve (AUC) of lumbar BMD improvement was 0.871. With P = 0.739 as the cutoff value, the specificity was 89.3%, and the sensitivity was 73.5%. The final predictive model was internally validated using the bootstrap re-sampling procedure that calculated small AUC optimisms of -0.001 (95% CI -0.005-0.003). Conclusion: 24 h Ucr was negatively correlated with 1 year change in lumbar BMD after treatment with ZOL and the index P showed good predictive value for 1 year lumbar BMD improvement after treatment with ZOL. Disclosure J. Zeng: None. Y. Jing: None. N. Li: None. H. Sheng: None. Funding Grants from National Natural Science Foundation of China (No. 82170894); Program of Shanghai Science and Technology Committee (21S11901100); The Research Physician Project of Shanghai Tenth People's Hospital (2023YJXYSA014).

618-P: Development of a New Index Based on 24-Hour Urinary Creatinine to Predict Improvement of Lumbar Spine BMD after One Year of Zoledronic Acid Treatment for Osteoporosis