Protein, Total, Urine

Overview:

Evaluate proteinuria, eg, following urinalysis in which proteinuria is detected; evaluate renal diseases, including proteinuria complicating diabetes mellitus, the nephritic syndromes, eg, lipoid nephrosis, membranous, proliferative glomerulopathies, metal poisoning (eg, gold, lead, and cadmium), renal vein thrombosis, systemic lupus erythematosus (SLE), constrictive pericarditis and amyloidosis; work up other renal diseases including malignant hypertension, glomerulonephritis, Goodpasture syndrome, Henoch-Schonlein purpura, thrombotic thrombocytopenic purpura, collagen diseases, cryoglobulinemia, toxemia of pregnancy, drug nephrotoxicity,hypersensitivity reactions, allergic reactions, and renal tubular lesions; manage myeloma and macroglobulinemia of Waldenstrom (Bence Jones proteinuria); evaluate hypoproteinemia. Tubular proteinurias include Wilson diseaseand Fanconi syndrome. Normal urine protein consists of albumin (less than or equalto 35 mg/24 hours) and other plasma proteins (ie,globulins, haptoglobin, beta2-microglobulin, and light chain). Tamm-Horsfall glycoprotein secreted by renal tubular cells may contribute less than or equal to 50 mg/24 hours. Urinaryprotein in normal levels tends to increase with age, exercise and standing posture. Although quantitative protein can be run on a random specimen or timed collections less than 24 hours, 24-hour collections are preferable for evaluation of the nephrotic states and inflammatory renal disorders. Creatinine, creatinine clearance, BUN, serum protein electrophoresis, ANA, anti-DNA antibodies, HIV, hepatitis C antibody, hepatitis B antigen, and complement levels (including total complement, C3, C4) are among useful tests to work up patients with proteinuria. Urine electrophoresis, immuno- fixation, and immunoelectrophoresis are useful in patients older than 35 years of age to investigate possible diagnosisof amyloidosis, myeloma, and Waldenstrom macroglobulinemia. Some patients exhibit orthostatic proteinuria (ie, recumbenturine protein 100-180 mg) in a 12-hour overnight urine coll-ection and 1 g in the subsequent 12 hours while ambulatory. The presence of >200 mg of urinary protein in the overnight specimen or equally increased amounts of urine in both specimens indicate a need for further work-up.[1] Nephrotic syndromes are the cause of the most severe urinary protein losses. Nephrotic syndrome is defined now usually by the degree of proteinuria (ie, proteinuria >50 mg/kg/day). After time, additional signs and symptoms occur,including hypoproteinemia, hypoalbuminemia, elevation of alpha-globulin (with decreased gamma-globulin on electro- phoresis), hyperlipidemia, and edema. Urinary albumin is a more sensitive marker of progression and regression of renaldisease than urine total protein, especially when urine total protein is <300 mg/g creatinine.[2] Urine albumin is available from protein electrophoresis following concentra- tion procedures; however, this method is not sensitive to low concentrations of albumin.[2]

Although evaluation for proteinuria may be the best single test to work up chronic renal disease, proteinuria may wax and wane. Toxemia is a state in which urine protein excretion is commonly measured. The standard for most methodologies is albumin. The different methods are more or less sensitive to globulin than to albumin. For nonselectiveproteinurias, where a variety of proteins are present, the different methodologies will yield different results. Twenty-four hour urine collections are subject to collection errors. Phenazopyridine (Pyridium(R)) interferes with the reaction by causing color interference. Functional and postural proteinuria occur.