Most cases of proteinuria can be classified as glomerular, tubular, or overflow proteinuria.
Glomerular proteinuria
- Urine total protein: 1-20 g/day.
- Passage of protein from glomerular capillary blood (mainly albumin) into the urine.
Tubular proteinuria
- Urine total protein: <2 g/day.
- Passage of low molecular weight proteins (e.g., retinol-binding protein, alpha-2-microglobulin, beta-2-microglobulin) into the urine.
Overflow proteinuria
- Urine total protein: up to 20 g/day.
- Overproduction of small proteins (e.g., myoglobin, light chains) leads to increased glomerular filtration and appearance in the urine.
Read more here
http://www.aafp.org/afp/2000/0915/p1333.html
https://www.uptodate.com/contents/assessment-of-urinary-protein-excretion-and-evaluation-of-isolated-non-nephrotic-proteinuria-in-adults