LAUSR

The aim of the study was to analyse the utility of retinol binding protein (RBP) in case of renal impairment in MM patients and investigate its relationship with acclaimed parameters of renal failure and markers of MM stages. We recruited 73 patients (35 women, 38 men, in age range of 29-90 years, mean 70 ± 10 years) with multiple myeloma (MM), including 6 (8%) with smoldering MM, 40 (55%) with International Staging System (ISS) stage I, 15 (21%) with ISS II and 12 (16%) with ISS III. The majority of patients (65, 89%) received at least one treatment scheme. Thirty patients (41%) received maintenance treatment at recruitment. Median eGFR based on serum creatinine (CKD-EPICr) equaled 67 (range 9 – 117) ml/min/1.73 m2. Significant correlation was observed between RBP and the ordered variable describing MM stage from smoldering myeloma to ISS III (R=0.36; p=0.002). There were no differences between patients in CR, PR, SD and PD at the time of samples’ collection. Patients who were on maintenance treatment at recruitment tended to have higher serum RBP (median 42.6 versus 37.7 mg/l), however, the difference was not statistically significant (p=0.068). The patients who received steroid treatment had significantly higher RBP concentrations. There were no such association with other medications. There was no association between RBP and the number of previous treatment lines (p=0.8). Serum RBP did not differ between men and women (p=0.7) and did not correlate with age (p=0.6). Significant correlations were found between RBP and serum creatinine, cystatin C and eGFR values calculated based on creatinine and/or cystatin C (Table 1). In multiple regression, serum creatinine or cystatin C and the treatment with steroids were associated with RBP independently of ISS stage (Table 2). Moreover, RBP correlated with β2-microglobulin, LDH, leukocyte count, α-klotho, FGF-23, GDF-15, uNGAL and uIGFBP-7, however, only the associations with β2-microglobulin and sTfR were independent of serum creatinine in multiple regression (Table 1). Baseline serum RBP concentration was significantly correlated with eGFR after a median of 19 months follow-up (range 1-24 months) (R=-0.35; p=0.003), however, the correlation was not independent of baseline serum creatinine ((beta ± SE: 0.06 ± 0.10; p=0.5). To the contrary, baseline serum cystatin C (beta ± SE: -0.36 ± 0.13; p=0.009) predicted final eGFR independently of baseline serum creatinine. RBP may be useful marker in renal damage in patients with chronic kidney injury among patients with MM. This can lead to noninvasive biomarker-targeted diagnostic interventions and contribute to early beginning of treatment that may improve life expectancy quality of life in MM.