Clinical and Interpretive

This assay is useful in the evaluation of renal disease and for screening for monoclonal gammopathy.

Protein in urine is normally composed of a combination of plasma-derived proteins that have been filtered by glomeruli and have not been reabsorbed by the proximal tubules and proteins secreted by renal tubules or other accessory glands.

Increased amounts of protein in the urine may be due to:
-Glomerular proteinuria: caused by defects in permselectivity of the glomerular filtration barrier to plasma proteins (eg, glomerulonephritis or nephrotic syndrome)
-Tubular proteinuria: caused by incomplete tubular reabsorption of proteins (eg, interstitial nephritis)
-Overflow proteinuria: caused by increased plasma concentration of proteins (eg, multiple myeloma, myoglobinuria)

Total protein >500 mg/24 hours should be evaluated by immunofixation to determine if a monoclonal immunoglobulin light chain is present, and if so, identify it as either kappa or lambda type.

Urinary protein levels may rise to 300 mg/24 hours in healthy individuals after vigorous exercise.

Low-grade proteinuria may be seen in inflammatory or neoplastic processes involving the urinary tract.

In a random urine specimen, a protein/creatinine or protein/osmolality ratio can be used to roughly approximate 24-hour excretion rates. False-positive urine protein levels (increased) may be due to contamination of urine with menstrual blood, prostatic secretions, or semen. Protein electrophoresis and immunofixation may be required to characterize and interpret the proteinuria.