Neutrophil Gelatinase-Associated Lipocalin (NGAL) and Cystatin-C Are Sensitive Markers of Renal Injury in Patients with Multiple Myeloma,
Authors: Terpos Evangelos , Papassotiriou Gerasimos-Petros , Kastritis Efstathios , Gkotzamanidou Maria , Christoulas Dimitrios , Eleutherakis-Papaiakovou Evangelos , Margeli Alexandra , Migkou Magdalini , Gavriatopoulou Maria , Roussou Maria , Papassotiriou Ioannis , Dimopoulos Meletios Athanasios 
Published: October 2019

Abstract
Abstract 3918
Renal impairment (RI) is a common complication of patients with multiple myeloma (MM). The evaluation of RI is based mainly on the estimation of glomerular filtration rate (GFR) using the MDRD equation. However, MDRD formula has greater value in patients with stabilized serum creatinine, while the majority of MM patients have acute renal damage. Thus, it is of great importance to evaluate novel markers of kidney injury in MM setting. Neutrophil gelatinase-associated lipocalin (NGAL) is a 25 KDa protein which is overproduced by proximal tubular cells in response to injury. NGAL is upregulated within 2 hours of injury, well before functional changes are observed in both preclinical and clinical studies. NGAL has never been evaluated in MM. Cystatin-C (Cys-C) is a cysteine protease inhibitor which provides a better reflection of GFR (renal tubular function) than serum creatinine. The aim of the study was to evaluate NGAL and Cys-C in MM and explore possible correlations with patients' RI.
We studied: i) 64 patients with newly diagnosed myeloma: 16 with asymptomatic disease (7M/9F; median age 59 years, range 37–82 years) and 48 with symptomatic myeloma (30M/18F; median age 70 years, range 45–89 years; ii) 8 patients with MGUS (4M/4F; median age 72 years, range 39–84 years); and iii) in 20 healthy, gender and age-matched controls. Serum Cys-C was measured on the Behring Nephelometer-II analyser using a latex particle-enhanced nephelometric immunoassay (Dade Behring, Liederbach, Germany). Serum NGAL was measured using an ELISA methodology (Quantikine, R&D Systems, Minneapolis, MN, USA). eGFR was evaluated using the MDRD formula.
Twenty-six (54%) patients with symptomatic MM had eGFR >60 ml/min, while 12 (25%) had eGFR 30–60 ml/min and 10 (21%) eGFR <30 ml/min. All patients with asymptomatic MM and MGUS had an eGFR >60 ml/min. However, NGAL serum levels were elevated in patients with both asymptomatic (median: 91.7 μg/l, range: 29.5–206.4 μg/l) and symptomatic MM (115.4 μg/l, 15.4–417.3 μg/l) compared to controls (52.5 μg/l, 26.5–72.6 μg/l; p<0.001 for both comparisons). Even MGUS patients had elevated NGAL values compared to controls (116.5 μg/l, 74.9–205.5 μg/l; p<0.01). Only patients with symptomatic MM had increased levels of Cys-C compared to controls (1.37 mg/L, 0.7–4.0 mg/l vs. 0.7 mg/l, 0.6–1.0 mg/l; p<0.01). NGAL strongly correlated with Cys-C (r=0.506, p<0.001) and eGFR (r=-0.457, p<0.01), while Cys-C showed also strong correlation with eGFR (r=-0.804, p<0.001) as well as with ISS (ISS-3 had higher values of Cys-C compared to ISS-2 and ISS-1, p-ANOVA<0.001), beta2-microglobulin (r=0.434, p=0.002), high sensitivity CRP (r=0.364, p=0.012), serum interleukin-6 (r=0.349, p=0.016) and age (r=0.339, p=0.019). Regarding eGFR, the median levels (range) of NGAL were 97.8 μg/l (17.5–244.2 μg/l), 151.2 μg/l (15.4–232.3 μg/l) and 233.4 μg/l (101.7–417.3 μg/l) for patients with eGFR >60 ml/min, 30–60 ml/min and <30 ml/min, respectively (p-ANOVA<0.001). The respective median values for Cys-C were: 0.9 mg/l (0.7–2.0 mg/l), 1.5 mg/l (1.1–3.2 mg/l) and 2.9 (1.7–3.9 mg/l) for patients with eGFR >60 ml/min, 30–60 ml/min and <30 ml/min (p-ANOVA<0.001). The ROC analysis showed that NGAL values of >50.5 μg/l have a 80.8% sensitivity and 86.4% specificity for eGFR <60 ml/min (AUC=0.764). Similarly, Cys-C values of >1.15 mg/l have a 73.1% sensitivity and 100% specificity for eGFR <60 ml/min (AUC=0.941). Median levels of Cys-C were higher in patients with BJ proteinuria ≥200 mg/day (1.6 mg/l, 0.7–3.9 mg/l) compared to all others (1.1 mg/l, 0.7–1.9 mg/l; p=0.003). The respective values of NGAL for patients with BJ proteinuria ≥200 mg/day vs. <200 mg/day were: 169.7 μg/l (15.4–417.3 μg/l) vs. 105.5 μg/l (35–212.7; p=0.099). The ROC analysis showed that NGAL values of >61.7 μg/l have a 76.9% sensitivity and 81% specificity for BJ proteinuria ≥200 mg/day (AUC=0.641), while Cys-C values of >1.5 mg/l have a 92.3% sensitivity and 76.2% specificity for BJ proteinuria ≥200 mg/day (AUC=0.941).
Our data suggest that both NGAL and Cys-C are very sensitive markers that reflect RI in newly-diagnosed patients with multiple myeloma. The high levels of NGAL in asymptomatic MM patients and in MGUS patients may indicate the presence of subclinical renal damage in these patients early in the course of their disease and may reveal NGAL as an early marker that predicts the development of RI in MM.

Disclosures:
No relevant conflicts of interest to declare.