A capillary electrophoresis-derived nomogram for identifying IgM monoclonal proteins missed by serum protein electrophoresis.

OBJECTIVES: We developed and internally validated a quantitative nomogram integrating capillary electrophoresis (CE)-derived migration-time parameters with routine laboratory variables to differentiate IgM-type from non-IgM-type monoclonal gammopathy (MG) among SPE-negative but IFE-positive patients. METHODS: This retrospective study included 346 patients with SPE-missed MG. Clinical, biochemical, and CE-derived time parameters were evaluated. Following LASSO regression screening, multivariate logistic regression identified independent predictors. The nomogram was internally validated using a training set (n = 242) and a test set (n = 104). Performance was assessed by area under the curve (AUC), calibration curves, and decision curve analysis (DCA). RESULTS: Six predictors were retained: age, IgM level, LDL-C, α1 globulin, β2 globulin, and the albumin-α1 time difference, which was significantly prolonged in IgM cases (OR = 1.686, P = 0.004). The nomogram achieved an AUC of 0.863 (95% CI: 0.797-0.929) in the training set and 0.697 (95% CI: 0.556-0.838) in the held-out test set, with a test-set sensitivity of 38.9% and specificity of 80.2%. Internal resampling via bootstrapping yielded a corrected AUC of 0.858, which serves as an internal estimate rather than an independent result. Calibration and DCA demonstrated good agreement and net clinical benefit. CONCLUSIONS: CE-derived migration-time parameters add objective quantitative value to routine indices, facilitating pre-triage of occult IgM-type MG. This nomogram can be embedded into laboratory information systems for risk stratification, pending multi-center external validation.