What causes high urinary a1 microglobulin?

α1-microglobulin is a glycoprotein produced by hepatocytes and lymphocytes. α1-microglobulin in plasma can exist in two forms: free α1-microglobulin can freely penetrate glomeruli, but about 99% α1-microglobulin in original urine is reabsorbed and decomposed by proximal convoluted tubule epithelial cells, and only a small amount is excreted in urine. For α1-microglobulin in urine, the first consideration is the impairment of proximal tubular function. The increase of α1-microglobulin in urine is a sensitive index reflecting the specificity of early proximal tubular function damage caused by various causes. Compared with β2-microglobulin, it is not affected by malignant tumor and other factors, and acidic urine will not show false negative, so it is more reliable. Meanwhile, α1-microglobulin also has value in evaluating glomerular filtration function. The increase of α1-microglobulin in serum often indicates blood retention caused by GFR decrease. β2-MG and α1-MG are ideal indicators for evaluating glomerular and proximal tubular function caused by various causes, especially in early stage of injury, but α1-MG is the best one and tends to replace β2-MG at this stage.