The ratio of serum urea nitrogen to albumin is a better predictor of OS in MM patients than urea nitrogen alone.

Introduction Multiple myeloma (MM) is a malignant proliferative disease of plasma cells. Abnormally cloned plasma cells secrete large amounts of monoclonal immunoglobulins in the bone marrow of MM patients. Serum urea nitrogen (sUN) is a byproduct of protein metabolism, and its effect on MM patients' prognoses remains unknown. Therefore, we analysed MM patients' clinical data to explore the role of sUN and serum urea nitrogen/serum albumin (sUAR) in the baseline tumor load and MM prognosis of MM patients. Methods We downloaded the clinical data of 762 MM patients from the MMRF database. After excluding those without baseline sUN, 452 patients were finally included in the study. Smoothed curve fitting, threshold analysis, Tamhane's T2 test, multivariate adjusted Cox regression analysis, Kaplan‒Meier (K-M) curves, and receiver operating characteristic (ROC) analysis were applied in the study. Results There were 452 newly diagnosed MM patients included in this study. In most patient groups, sUN and sUAR were positively linked with β2-microglobulin (β2-MG) and lactic dehydrogenase (LDH) according to smoothing curve fitting and threshold analysis. The higher the ISS stage, the greater the values of sUN and sUAR. Furthermore, smoothed curve fitting and threshold analysis showed that sUN was correlated with OS, although sUAR had a stronger correlation with OS and could be applied to a broader group. The results of a multivariate adjusted Cox regression analysis demonstrated that sUN and sUAR were independent prognostic factors for OS. The K-M curve confirmed the correlation between higher sUN and sUAR levels and worse OS. β2-MG and LDH are generally recognized prognostic factors of OS. ROC analysis revealed that sUN might boost β2-MG and LDH's predictive value and sUAR had a higher predictive value. Conclusion This retrospective study based on the MMRF database showed that high sUN and sUAR levels were positively associated with β2-MG, LDH, and ISS staging, and sUAR exhibited a stronger correlation with OS than sUN alone.