Usefulness of serum globulin levels for discriminating patients with monoclonal gammopathies/ paraproteinemias

Introduction and Aim: The confirmatory step in diagnosis of monoclonal gammopathies is bone marrow biopsy and presence of M-protein in serum protein electrophoresis. These tests are relatively expensive & invasive for screening and unavailable in low resource settings. Increased levels of serum globulin are clue to the diagnosis of monoclonal gammopathy. The aim of this study was to assess the relevance of serum globulin levels in discriminating between patients with & without monoclonal gammopathies/ paraproteinemia. Materials and Methods: We retrospectively reviewed serum protein electrophoresis (SPE) and related investigations of patients suspected of monoclonal gammopathy. Reports with an M-band were considered as paraproteinemias, and those without as controls. ROC for sensitivities & specificities for serum globulin levels were computed. Results: For the case-control study, median serum globulin values in cases were 4.4 (3.5-6.3) g/dL in males and 3.65 (3.33-5.0) g/dL in females. They were significantly higher than those with normal SPE pattern, with a p <0.001. A cut-off value of 3.25 g/dL of globulin could distinguish between paraproteinemias and controls with a sensitivity of 82.1% and specificity of 85.4% in males; a sensitivity of 79.2%, a specificity of 76.7% for females. At a cut-off value of 3.4 g/dL, sensitivity was 77% and specificity 92.7% for males; sensitivity was 75% and specificity 83.7% for females. Alternatively, a cut-off value of 0.458 of globulin/total protein ratio could distinguish at a best sensitivity & specificity of 80% and 89% in males; 83.3% and 83.7% in females. Conclusion: Serum globulin values and globulin/total protein ratio can reliably differentiate patients with paraproteinemias.