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Background: Urine protein electrophoresis (PEP) is widely employed to detect proteinuria and monoclonal protein (M protein), which is important for diagnosing and monitoring multiple myeloma. However, the appearance of unusual bands can confound the interpretation.
Methods: We described two clinical cases in which a distinct beta-region band in urine PEP associated with hematuria. To investigate this phenomenon, we conducted an experiment by adding both lysed and non-lysed red blood cells (RBCs) to normal urine specimens and then performed urine PEP.
Results: In both of our cases, the beta-region band disappeared after hematuria improved. In the experimental setup, the group with RBC lysis at counts above 500/µL produced a marked band in the beta region without gross hematuria, whereas the group with non-lysed RBCs required much higher concentrations to generate faint bands.
Conclusions: Our findings demonstrate that hematuria, particularly when red blood cells undergo lysis, can produce a distinct band in the beta region on urine PEP that may be misinterpreted as a monoclonal protein. Careful correlation with urinalysis results is therefore crucial to prevent misdiagnosis, especially in patients with microscopic hematuria.
DOI: 10.7754/Clin.Lab.2025.250121
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