Alpha1 microglobulin (α1-M), sometimes referred to as human complex forming protein (HC), is a small, low molecular weight (33kDa) globular glycoprotein. Its physiological concentration in urine is very low. It is one of the most constant microproteins present in urine in cases of tubular damage. It is filtered by the glomerulus and then reabsorbed almost completely by the proximal tube where it will be broken down. Because of its sensitivity and stability even in acidic urine, it represents an early marker of choice for diagnosing tubular lesions in nephritis, advanced diabetic nephropathies, following the administration of nephrotoxic drugs or after exposure to heavy metals.