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 >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-creatinine ratio for males 18 to 83 years is <0.11 mg/mg creatinine and for females 18 to 83 years is <0.16 mg/mg creatinine. The normal protein-to-osmolality ratio is <0.27.(1) For patients <18 years of age and >83 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-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.
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.
Males <0.11 mg/mg creatinine
Reference values have not been established for male patients <18 years of age.
Reference values have not been established for male patients >83 years of age.
Females <0.16 mg/mg creatinine
Reference values have not been established for female patients <18 years of age.
Reference values have not been established for female patients >83 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. 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, ASM Press, 1997, pp 65-74