Beta-2-Microglobulin is a low-molecular weight protein found on the cell surfaces of all nucleated cells and shed into the blood, particularly by tumor cells and lymphocytes. Due to its small size, it passes through the glomerular membrane, but normally less than 1% is excreted due to reabsorption in the proximal tubules of the kidney. Therefore, high plasma levels of BMB occur in renal failure, inflammation, and neoplasms, especially those associated with B-lymphocytes. It’s particularly useful in monitoring kidney transplant recipients.