Protein, Total, 12 Hour, Urine
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
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 more than 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 greater than 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.
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.
<163 mg/12 hours (day or night collection)
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. 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. Robinson RR: Isolated proteinuria in asymptomatic patients. Kidney Int 1980;18:395-406
4. Dube J , Girouard J, Leclerc P, Douville P: Problems with the estimation of urine protein by automated assays. Clin Biochem 2005 May;38(5):479- 485
5. Koumantakis G, Wyndham, L. Fluorescein interference with urinary creatinine and protein measurements. Clin Chem 1991 Oct;37(10 Pt 1):1799