Suspicious bands in serum and urine protein immunofixation electrophoresis tests in patients with and without a history of monoclonal gammopathies: a retrospective database study

INTRODUCTION: Electrophoresis tests are reported as negative, positive, or-rarely-as suspicious for monoclonal band (SfMB). This study aimed to determine the fate of patients with SfMB findings in long-term follow-up. METHODS: Patients with SfMB results obtained in 2019 were retrospectively identified. These patients were examined for the presence of any control electrophoresis test until their most recent hospital visit in 2025. RESULTS: In 2019, electrophoresis tests were reported for a total of 1289 patients. In total, 115 patients with no prior electrophoresis test results were reported as positive (newly diagnosed patients) and 30 patients with no prior electrophoresis test results were reported as SfMB. Among the 30 SfMB cases, control electrophoresis tests had yielded a positive result in 2 patients and a negative result in 12 patients. In the remaining 16 patients, 7 were without control electrophoresis test results but had long clinical follow-up, whereas 9 were without a control electrophoresis test result and clinical follow-up. In 357 patients with a previously diagnosed monoclonal gammopathy, 18 were reported as SfMG. DISCUSSION: None of the patients initially reported as having an SfMB developed monoclonal gammopathy during their follow-up period. We recommend that cases reported as "suspicious" be managed separately in patients with and without a prior monoclonal gammopathy diagnosis, where the term "weak positive" may be more appropriate in patients with a known monoclonal gammopathy.