Protein, Total, Random, Urine
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
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)
Evaluation of renal disease
Screening for monoclonal gammopathy
Total protein of greater than 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. The normal protein-to-osmolality ratio is less than 0.42.(1) For patients less than 18 years of age no reference range has been established.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
False-proteinuria may be due to contamination of urine with menstrual blood, prostatic secretions, or semen.
The urinary protein concentration may rise to 300 mg/24 hours in healthy individuals after vigorous exercise.
Normal newborn infants may have higher excretion of protein in urine during the first 3 days of life.
The presence of hemoglobin elevates protein concentration.
Samples should be collected before fluorescein is given or not collected until at least 24 hour later.
Protein electrophoresis and immunofixation may be required to characterize and interpret the proteinuria.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
<0.18 mg/mg creatinine
Reference values have not been established for patients <18 years of age.
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Wilson DM, Anderson RL: Protein-osmolality ratio for the quantitative assessment of proteinuria from a random urinalysis sample. Am J Clin Pathol 1993 Oct;100(4):419-424
2. Morgenstern BZ, Butani L, Wollan P, et al: Validity of protein-osmolality versus protein-creatinine ratios in the estimation of quantitative proteinuria from random samples of urine in children. Am J Kidney Dis 2003 Apr;41(4):760-766
3. 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
4. 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
5. Robinson RR: Isolated proteinuria in asymptomatic patients. Kidney Int 1980;18:395-406
6. Dube J, Girouard J, Leclerc P, et al: Problems with the estimation of urine protein by automated assays. Clin Biochem 2005;(38):479-485
7. Koumantakis G, Wyndham L: Fluorescein Interference with Urinary Creatinine and Protein Measurements. Clin Chem 1991;37(10):1799