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Background: Renal impairment is a common complication of patients with multiple myeloma (MM). We aimed to evaluate the clinical significance of 2 newly discovered biomarkers of renal injury, cystatin C (CysC), a protein reflecting glomerular filtration rate, and neutrophil gelatinase-associated lipocalin (NGAL), a protein reflecting tubular injuries., Patients and Methods: We studied 64 patients with newly diagnosed myeloma: 16 with asymptomatic (smoldering) MM and 48 with symptomatic myeloma; 8 patients with monoclonal gammopathy of undetermined significance (MGUS); and 20 healthy control subjects. Along with common blood and urine chemistry determinations, measurements of CysC, NGAL, β2-microglobulin, high-sensitivity C-reactive protein, and interleukin 6 were performed., Results: We found that only patients with symptomatic MM had increased levels of CysC compared to controls (P < .01); that serum NGAL levels were elevated in all patients compared to controls P < .001; that NGAL strongly correlated with both estimation of glomerular filtration rate (eGFR) (CysC) and eGFR (Modification of Diet in Renal Disease [MDRD] formula) (r = 0.616, P < .0001; and r = -0.371, P < .01, respectively); that CysC showed strong correlation with eGFR (r = -0.782, P < .001) and with the International Scoring System (ISS) (more pronounced in patients with ISS-3); and that receiver operating characteristic curve analysis showed that NGAL values of > 50.5 μg/L have a 80.8% sensitivity and 86.4% specificity for eGFR < 60 mL/min (area under the curve = 0.764)., Conclusion: These findings suggest that both NGAL and CysC are very sensitive markers that reflect renal impairment in newly diagnosed patients with MM. The high levels of NGAL in asymptomatic patients and in MGUS patients support the hypothesis of the presence of renal damage in these patients early in the course of their disease and may reveal NGAL to be an early marker that predicts the presence of renal impairment in MM., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Objectives: Monoclonal gammopathy of undetermined significance (MGUS) occurs without other symptoms, although monoclonal proteins can cause kidney injuries. Here, we assessed kidney function and identified the best follow-up parameters in patients with MGUS without kidney damage symptoms., Methodology: Forty-six patients with MGUS were included in the study group. The control group (CRT, n = 23) consisted of healthy subjects matched for age and sex. Serum cystatin C was determined using an immunonephelometric method, serum and urine neutrophil gelatinase-associated lipocalin (NGAL) was measured with an immunoenzymatic method, and cathepsin B activity was determined fluorometrically., Results: Serum cystatin C and urine NGAL were higher, and serum NGAL was lower in MGUS patients compared with CRT. Neither serum cystatin C, nor serum or urine NGAL, correlated with the biomarkers of MGUS. The serum activity of cathepsin B did not differ between groups and did not correlate with serum cystatin C. Serum cystatin C correlated with serum creatinine, while serum NGAL did not correlate with serum creatinine or cystatin C. The estimated glomerular filtration rates (eGFRs) in MGUS were within normal range and correlated with serum cystatin C. The strongest correlation was observed for CKD-EPI. Seven patients presented with albuminuria >30 mg/day. There was a correlation between albuminuria in this group and λ free light chains., Conclusions: The kidney function in MGUS patients is impaired, although there are no clinical and standard laboratory test manifestations. Cystatin C and urine, but not serum, NGAL should be considered markers for kidney injury. CKD-EPI is recommended for eGFR assessment., (© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)