Significance of the pee-value: relevance of 24-hour urine studies for patients with myeloma.

International Myeloma Working Group (IMWG) response criteria require refrigerated 24-hour urine specimens for most patients. However, given that serum free light chain testing has been shown to outperform 24-hour urine immunofixation as a prognostic marker, the importance of maintaining urine testing options or requirements within each level of IMWG response criteria has not been investigated. We analyzed responses to induction therapy for all transplant-eligible patients with multiple myeloma at our institution over a 3-year period using traditional versus 'urine-free' IMWG response criteria (where references to urine were removed from the descriptions for every depth of response). Of 281 evaluable patients, responses changed for only 4% of patients (95% confidence interval 2-7%) using urine-free criteria. Our results call into question the continued requirement for 24-hour urine measurements as part of IMWG response assessments for all patients. Research into the prognostic performance of urine-free IMWG criteria is ongoing.