A comparison of 24-hour urine versus random urine samples for determination and quantification of Bence Jones protein in a South African population.
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Objectives: The International Myeloma Working Group (IMWG) and College of American Pathologists recommend a 24-hour collection for Bence Jones proteins(BJP). Although a 24-hour urine collection is a definitive means to determine BJP excretion, it has several issues related to sample collection and is prone to inaccuracy. Protein to creatinine ratios have demonstrated good correlation with 24-hour urine. The aim of this study was to compare measured 24-hour urine to random urine collections for the quantitation of BJP in a South African population. Method: Known patients with multiple myeloma(MM) collected 24-hour urine as part of their routine clinical assessment for BJP, random urine samples were submitted following completion of the 24-hour collection. The measured 24-hour urine BJP was then compared to 2 estimated 24-hour BJP excretions which were calculated as follows; Estimation 1 (E1): Estimated 24-hour BJP (mg/24hour) = Urine BJP/Creatinine ratio (mg/mmol) ´ 10, Estimation 2 (E2): Estimated 24- hour BJP (mg/24hour) = Urine BJP/Creatinine ratio (mg/mmol) ´ 15mg/kg for women or ´20mg/kg for men. All the 24-hour BJP results were classified according to IMWG treatment response criteria. Results: When using the Wilcoxon paired test analysis, the measured 24-hour urine BJP was significantly different to both the E1 (p=0.049) and E2 (p=0.049) equations. But analysis following categorization of each patient per IMWG BJP response criteria, indicated no significant difference in classification of treatment response using either the E1 or E2 estimation equations (P=0.69). Conclusion: 24-hour urine collections are cumbersome. Random urine BJP estimates are simple, rapid and inexpensive. This study demonstrates that both the estimates of 24-hour BJP can be used to monitor response in patients with MM. This can be added to the body of evidence that random samples can be used to monitor patients’ treatment response in MM.