Serum free light chain (FLC) concentration is greatly affected by kidney function. Using a large prospective population-based cohort, we aimed to establish a reference interval for FLCs in persons with chronic kidney disease (CKD). A total of 75422 participants of the iStopMM study were screened with serum FLC, serum protein electrophoresis and immunofixation. Estimated glomerular filtration rate (eGFR) was calculated from serum creatinine. Central 99% reference intervals were determined, and 95% confidence intervals calculated. Included were 6461 (12%) participants with measured FLCs, eGFR < 60 mL/min/1.73 m2, not receiving renal replacement therapy, and without evidence of monoclonality. Using current reference intervals, 60% and 21% had kappa and lambda FLC values outside the normal range. The FLC ratio was outside standard reference interval (0.26–1.65) in 9% of participants and outside current kidney reference interval (0.37–3.10) in 0.7%. New reference intervals for FLC and FLC ratio were established. New reference intervals for the FLC ratio were 0.46–2.62, 0.48–3.38, and 0.54–3.30 for eGFR 45–59, 30–44, and < 30 mL/min/1.73 m2 groups, respectively. The crude prevalence of LC-MGUS in CKD patients was 0.5%. We conclude that current reference intervals for FLC and FLC ratio are inaccurate in CKD patients and propose new eGFR based reference intervals to be implemented.

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High proportion of patients with multiple myeloma suffer from comorbidities which may alter clinical management. Therefore, our aims were to evaluate the prevalence of comorbidities and their impact on survival. We included patients diagnosed with multiple myeloma 1990‐2013 in Sweden and all diagnoses from each patient from 1985. A total of 13 656 patients with multiple myeloma were included in the study, thereof 7404 (54%) had comorbidity at diagnosis. The risk of death was increased for those with one comorbidity at diagnosis compared to those without any comorbidity (hazard ratio = 1.19; 95% confidence interval:1.14‐1.25); this risk was higher for those with two (1.38; 1.30‐1.47) and three or more comorbidities (1.72; 1.62‐1.83). Furthermore, the risk of death was increased in patients with prior history of cancer, arrhythmia, heart failure, diabetes mellitus, cerebrovascular disease, chronic lung disease, psychological disease, peptic ulcer, neurological disease, peripheral vascular disease, chronic kidney disease, dementia, and inflammatory bowel disease. This large study shows that over 50% of multiple myeloma patients have a comorbidity at diagnosis and survival decreased with increasing numbers of comorbidities. This emphasizes the importance of comorbidities when evaluating patients and deciding on treatment strategies for individuals with multiple myeloma.

Multiple myeloma causes lytic bone lesions and fractures. The impact of fractures on multiple myeloma survival is unclear. The aim of this study was to evaluate the effect of fractures on survival in multiple myeloma using data from multiple myeloma patients diagnosed in Sweden in the years 1990-2013, identified from the Swedish Cancer Registry. Information on date of birth, multiple myeloma diagnosis, fractures, and death was collected from central registries.A Cox regression model was used to compare survival in patients with and without a fracture at multiple myeloma diagnosis and another Cox model was used with fracture as a timedependent variable to assess the effect of fracture on survival after multiple myeloma diagnosis. Results were adjusted for age, sex, year of diagnosis, and previous fractures. A total of 14,013 patients were diagnosed with multiple myeloma during the study, thereof 1,213 (8.7%) were diagnosed with a fracture at multiple myeloma diagnosis, and 3,235 (23.1%) after diagnosis. Patients with a fracture at diagnosis were at a significantly increased risk of death (hazard ratio=1.28; 95% confidence interval: 1.19-1.37). The risk of death was significantly increased in patients with a fracture after multiple myeloma diagnosis (2.00; 1.90-2.10). The impact of fractures on survival did not change significantly between the two calendar periods 1990-1999 and 2000-2013 (0.98; 0.89-1.08). Our large study shows that multiple myeloma patients with fractures are at a significantly increased risk of dying compared to those without fractures which stresses the importance of preventing bone disease in multiple myeloma.