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Urinary B2-Microglobulin Is a Good Indicator of Proximal Tubule Injury: A Correlative Study with Renal Biopsies

Acute kidney injury is a common clinical syndrome that is characterized by a rapid decline in kidney function, often triggered by glomerular disease and/or tubulointerstitial disease and associated with high morbidity and mortality. In addition to serum creatinine B2-microglobulin is a biomarker that can be used to determine underlying causes of acute kidney injury. B2-microglobulin is filtered almost completely through the glomeruli of the healthy kidney and then reabsorbed by the renal proximal tubules. Only a small amount of B2-microglobulin can be detected in the urine under normal physiological conditions. Therefore, levels of serum and urinary B2-microglobulin reflect the functions of glomeruli and proximal tubules.

In patients with acute kidney injury, an increase in serum creatinine, together with an increase in urinary B2-microglobulin, strongly suggests proximal tubule injury. However, a direct correlation between urinary B2-microglobulin and proximal tubule injury has not yet been fully established due to lack of a specific proximal tubule injury marker. Kidney injury molecule-1 (KIM-1) has been characterized as a selective proximal tubule injury marker. The researchers from Department of Pathology and Laboratory Medicine, Philadelphia, USA were done a study to examine the correlation between increase in urinary B2-microglobulin and proximal tubule injury assessed by KIM-1 staining in kidney biopsies. Between 2009 and 2012, 46 patients with urine B2-microglobulin had followup kidney biopsy. Diagnoses included glomerular and tubule-interstitial disease. Immunohistochemical staining for KIM-1 was performed and the intensity was graded from 0 to 3 . Linear regression analysis was applied to correlate the values of urinary B2-microglobulin and KIM-1 staining scores. P < 0.05 was considered statistically significant.

Result from this study demonstrated that thirty patients had elevated urinary B2-microglobulin. KIM-1 staining was positive in 35 kidney biopsies. There was a significant correlation between urinary B2-microglobulin and KIM-1 staining (P < 0.05). Sensitivity was 86.6%, specificity was 43.7%, positive predictive value was 74.2%, and negative predictive value was 63.6%.

Based on the results, the researchers were concluded that increased urinary B2-microglobulin was significantly correlated with KIM-1 staining in injured proximal tubules. Measurement of urine B2-microglobulin is a sensitive assay for proximal tubule injury.

Ref:
Zeng X, Hossain D, Bostwick DG, Herrera GA, Zhang PL. Urinary B2-Microglobulin Is a Good Indicator of Proximal Tubule Injury: A Correlative Study with Renal Biopsies. 2014(2014):1-7.