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Poster Session 8: Trauma and reconstruction| Volume 8, ISSUE 8, P645, September 2009

S115 Use of urinary beta-2 microglobulin (B2MG) as renal injury index

      Introduction and Objectives

      Human Beta-2 Microglobulin (B2MG) is a protein filtered by the glomeruli and reabsorbed by the proximal tubular cells where it is metabolized. B2MG is expressed on nucleated cells, and is found at low levels in the serum and urine of normal individuals and is considered as sensitive means for diagnosing tubular dysfunction. The aim of this study was to elucidate the relationship between urinary levels of B2MG and renal injuries and to correlate them with clinicopathological parameters. Our objective was to point out the value of urinary levels of B2MG as a cost effective, noninvasive diagnostic approach of diagnosis and evaluation of renal injuries.

      Material and Methods

      Urine samples of 85 patients with renal injuries were collected after 24 h, 2 days and 7 days for measuring B2MG. The control group consisted of 10 health subjects (<300 ng/ml). Exclusion criteria's were diseases that decrease renal function, such as inflammatory, viral and autoimmune diseases. The patients underwent clinical and laboratory tests and were also subject to image study by U/S and CT. Patients’ age ranged from 18 to 70 years (mean age = 42 years). Their diagnoses were reported as follows: 13 (15.3%) had Grade I, 21 (24.7%) had Grade II, 16 (18.8%) Grade III, 8 (9.4%) Grade IV and 12 (14.1%) Grade V. 15 patients (17.7%) with renal injury, microscopic hematuria and negative U/S and CT findings has been concluded in our study. All patients with Grade IV and V underwent nephrectomy due to hemodynamic instability. Relationship between B2MG and Grade of renal injury was evaluated with Kruskal-Wallis and confirmed by the Cochran- Armitage test for trend. Furthermore, we applied multivariate linear mixed effects models with B2MG as outcome, and age as an independent variable.

      Results

      In the urine sample of 15 patients with negative image study for renal injury, we detected B2MG with median value 524 ng/ml. A statistically significant negative relationship was found between levels of B2MG across the early period after renal injury (rs = −0.31, p-value = 0.004), meaning that when patients go to 7th day, this is followed by a decrease in B2MG. We observed that B2MG was associated with Grade (p-value < 0.001). Patients with Grade IV have 2579.7 ng/ml with 95% CI greater B2MG compared to patients in Grade 0 and subjects with Grade V have a 4956.5 ng/ml with 95% CI greater B2MG compared to patients in Grade 0, meaning that the level of B2MG is increased. We further observed that levels of B2MG of patients with Grade IV–V, who underwent nephrectomy were normalized in 2nd and 7th day postoperatively. No statistically significant association was obtained when correlating B2MG and age.

      Conclusions

      B2MG constitutes reliable index for renal injury and it can be used when the image study is not available or not diagnostic for renal injury and the suspicion is placed by the existence microscopic or macroscopic hematuria.