|Values are valid only on day of printing.|
Protein in urine normally consists of plasma proteins that have been filtered by glomeruli and not reabsorbed by the proximal tubule, and proteins secreted by renal tubules or other accessory glands. Increased amounts of protein in the urine may be due to:
-Glomerular proteinuria: defects in permselectivity of the glomerular filtration barrier to plasma proteins (eg, glomerulonephritis or nephrotic syndrome)
-Tubular proteinuria: incomplete tubular reabsorption of proteins (eg, interstitial nephritis)
-Overflow proteinuria: increased plasma concentration of proteins that exceeds capacity for proximal tubular reabsorption (eg, multiple myeloma, myoglobinuria)
-Urinary tract inflammation or tumor
In pregnant women, a urinary protein excretion of >300 mg/24 hours is frequently cited as consistent with preeclampsia, and 12-hour total protein excretion highly correlates with 24-hour values in this patient population.(1,2)
Orthostatic proteinuria is characterized by increased protein excretion in the upright position, but normal levels when supine. This condition can be detected by comparing urine protein levels in a collection split between day and night (see OPTU / Orthostatic Protein, Timed Collection, Urine). Orthostatic proteinuria is common in childhood and adolescence, but rare after age 30.
Evaluation of renal disease
Screening for monoclonal gammopathy
Screening for postural (orthostatic) proteinuria
In select clinical situations, collection of a 12-hour specimen may allow more rapid detection of proteinuria states (eg, screening pregnant patients for preeclampsia)
Total urine protein determined to be >500 mg/24 hours should be evaluated by immunofixation to assess if there is a monoclonal immunoglobulin light chain and, if present, 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.
False proteinuria 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.
<115 mg/12 hours (day or night collection)
Reference values have not been established for patients <18 years of age.
Reference values have not been established for patients >83 years of age.
1. Rinehart BK, Terrone DA, Larmon JE, et al: A 12-hour urine collection accurately assesses proteinuria in hospitalized hypertensive gravida. J Perinatol 1999;19:556-558
2. Adelberg AM, Miller J, Doerzbacher M, Lambers DS: Correlation of quantitative protein measurements in 8-, 12-, and 24-hour urine samples for diagnosis of preeclampsia. Am J Obstet Gynecol 2001 Oct;185(4):804-807
3. Keren DF: Clinical indications for electrophoresis and immunofixation. In Manual of Clinical Laboratory Immunology. Fifth edition. Edited by NR Rose, E Conway de Macario, JD Folds, et al. Washington, DC, Am Soc Microbiol, 1997, pp 65-74
4. Robinson RR: Isolated proteinuria in asymptomatic patients. Kidney Int 1980;18:395-406