Albumins are water–soluble proteins. They are synthesized in the liver and make up the majority of serum proteins. In the body of a healthy person, normally only a small amount of albumins with the smallest size, microalbumins, is excreted in the urine, since the renal glomeruli of an unaffected kidney are impervious to larger albumin molecules. In the initial stages of damage to the cell membranes of the renal glomerulus, more and more microalbumins are excreted in the urine, and as the lesion progresses, larger albumins begin to be released.

This process is divided into stages according to the amount of excreted proteins (from 30 to 300 mg / day, or from 20 to 200 mg / ml in the morning portion of urine, it is considered microalbuminuria, and more than 300 mg / day – proteinuria). Microalbuminemia always precedes proteinuria. Thus, microalbuminuria is understood as the excretion of albumin in the urine in an amount that exceeds the physiological level of its excretion, but precedes proteinuria.