Normal urine contains very little protein, usually less than 10 mg/dL. The majority of the protein that is found in normal urine is albumin.
The presence of an increased amount of protein in the urine (proteinuria) can be an indicator of renal disease. The two mechanisms that can lead to proteinuria are glomerular damage or a defect in the reabsorption process of the tubules in the nephron. The concentration of protein in the urine is not necessarily indicative of the severity of renal disease.
Severe proteinuria (greater than 3.5 g/day) is characteristically seen in patients with glomerulonephritis, lupus nephritis, lipoid nephrosis, and severe venous congestion of the kidney. Moderate proteinuria (0.5-3.5g/day) is seen in nephrosclerosis, multiple myeloma, diabetes nephropathy, malignant hypertension, and pyelonephritis with hypertension.
Mild proteinuria (less than 0.5 g/day) may be seen with polycystic kidneys, chronic pyelonephritis, benign orthostatic proteinuria, and some renal tubular diseases.
Transient proteinuria can also be due to physiologic conditions such as stress, exercise, cold exposure, and fever, in the absence of renal disease.