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Background: Serum protein electrophoresis (SPE), immunofixation, and free light chain assays are recommended for monoclonal gammopathy (MG) screening. High serum globulins might be an inexpensive and useful parameter to decide on a workup for MG. Objective: The objective of the study was to determine a serum globulin cutoff that predicts an abnormal SPE. Materials and methods: A retrospective, observational study performed in a hematological referral center. SPE, serum albumin, and globulins from patients with MG suspicion between January 2013 and August 2019 were collected. ROC curves for serum globulin and albumin/globulin ratio (A/G) were performed to identify their diagnostic yield for identifying the presence of M protein. Results: A total of 1578 SPE were collected; 1010 (64%) exhibited an M protein. After performing a ROC curve analysis, the best serum globulin value was ≥ 2.6 g/dL, with a sensitivity and specificity of 52% and 79.9%, respectively. Accordingly, the best A/G ratio cutoff (≤ 1.69) yielded a sensitivity of 58.9% and specificity of 79%. After a ROC curve sub-analysis on patients with an M protein ≥ 1 g/dL, the best serum globulin cutoff was ≥ 2.8 g/dL, with a sensitivity and specificity of 87.3% and 84.1%, respectively. The best A/G ratio cutoff was ≤ 1.38, with a sensitivity of 84.1% and specificity of 88.6%. Conclusions: A serum globulin and/or A/G cutoff can be used to guide the clinical decision-making for early detection of MG and could decrease its underdiagnosis. This inexpensive laboratory testing strategy could be used to screen adult populations above the age of 50 in a cost-efficient way.

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