“…FLC ratio can be normal, especially in pre-myeloma stages with low risk of progression, in younger patients, or in those subjects with concomitant increased of uninvolved light-chain levels [ 45 , 46 , 47 ]; however, this condition is not frequent in active MM, as reported in our case series (only 18% of patients, mostly with concomitant increased of uninvolved FLC), also in accordance with previously published studies [ 47 , 48 ]. Conversely, FCL ratio is abnormal in almost all non-secretory myeloma with a sensitivity close to 100% [ 16 , 17 , 18 , 19 ]. In our case series, we confirmed the high diagnostic potential of sFLC ratio for light-chain MM identification, and we also showed that the standardized values were highly correlated with renal failure, especially in light-chain MM.…”