Renal pathology and retinol status in multiple myeloma patients

Renal dysfunction is a common and serious complication in multiple myeloma (MM) patients. Renal proximal tubule injury is characteristic in MM, and may result in disturbed renal handling of various vitamins. The abnormal excretion of vitamins in urine may result in their low serum levels. The goal of this study was to investigate the urinary excretion of retinol in MM and its relationship with serum retinol concentration. For this purpose, 24 MM patients and 10 healthy individuals were studied. Serum and urinary retinol and retinol-binding protein (RBP) were measured by the high-performance liquid chromatography method and enzyme-linked immunosorbent assay, respectively. The study showed that 58% of MM patients excreted retinol in urine, while only 29% had elevated serum creatinine (P < 0.05). There was a strong and highly significant correlation between urinary retinol and RBP (r = 0.973, P < 0.006). Patients with normal and mildly elevated serum creatinine who excreted retinol in urine had a marked decrease in serum retinol (P < 0.007). On the other hand, serum retinol was not decreased in patients with moderate or severe renal failure, despite its urinary loss. Our data indicate that (i) urinary retinol is a more frequent marker of renal dysfunction than elevated serum creatinine in MM patients, (ii) serum retinol is decreased in MM with normal or mildly elevated serum creatinine, but not in patients with moderate/severe renal failure, and (iii) urinary retinol may serve as a diagnostic marker of renal proximal tubule dysfunction in MM patients.