24 Hour Urine Protein
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Reference-interval
- 10 - 140 mg/24 hours
Principle
- Detection of an abnormal amount of protein in urine is a reliable indicator of renal disease because protein has very low maximal tubular rate of reabsorption, so that increased filtration of production quickly saturates the reabsorptive mechanism. When proteinuria is confirmed, a 24-hour collection for protein excretion is made. This will indicate the degree of proteinuria.
- The ACA urine protein method uses a two-pack, end-point technique to measure urinary protein. The urine protein 1 (UP-1) pack provides a sample bland at 540 nm. In the UP-2 pack, benzethonium chloride (BEC) precipitates urinary protein in an alkaline medium. Light scattering by the precipitate causes a decrease in light transmission. The decrease in light transmission is measured as absorbance at 540 nm. The absorbance difference between the UP-1 and UP-2 pack is related to the total protein concentration in the sample by means of a standard curve or mathematical function.
Clinical-significance
- Normally there is a scant amount of protein in urine, up to about 150 mg/24 hours or 10 mg/dL, depending on the urine volume. The proteins are derived from plasma & the urinary tract. About one third is albumin, & the remaining plasma proteins include many small globulins.
- Healthy persons may exceed normal level during exercise or with dehydration. Proteinuria is a consistent finding after strenuous exercise. Proteinuria can occur in the absence of urinary tract disease in patients with hemorrhage or salt depletion & in febrile illnesses.
- Glomerular disease often causes heavy proteinuria, >3 to 4 g/day. Nephrotic syndrome is principally associated with glomerular diseases & diagnosed when the protein excretion is greater than 3.0 to 3.5 g/day. Losses of 10 to 20 g/day are found.
- Tubular disease is associated with loss of urinary protein that would otherwise be largely reabsorbed. These proteins are usually of low molecular weight. A tubular pattern proteinuria occurs with renal tubular diseases such as the Fanconi syndrome, cystinosis, Wilson's Disease, & pyelonephritis, & with renal transplantation rejection. The amount of proteinuria is lower than with glomerular diseases & is about 1 to 2 g/day.
- Bence Jones proteinuria is associated with multiple myeloma, macroglobulinemia, & malignant lymphomas. Excretion of Bence Jones protein in large amounts causes the tubular cells to become degenerated because of the high levels of protein reabsorbed.
- Postural proteinuria ( orthostatic) occurs in 3 to 5% of healthy young adults. In these persons, proteinuria is found during the day but not at night when a recumbent position is assumed. The total daily excretion of protein rarely exceeds 1 g.
Increases
Specimen
- 2 mL aliquot of a 24 hour urine collection. Proper 24 hour urine collection procedure should be followed, & collection should be refrigerated at 2-6 C during collection. Collections must be well mixed & a portion removed & allowed to come to room temperature. After it reaches room temperature, it must be well mixed again & then centrifuged to remove particulate matter before analysis.
- Specimens stored at 4 C with no additives are stable for at least three days. Specimens stored under toluene or those containing sodium hydroxide (5%) or boric acid (100 mg/mL) are acceptable.
- Specimens stored at room temperature with no additives will cause an approximately 10% increase in the protein level over a three- day period.
- Hydrochloric acid (0.1N) or boric acid (>200 mg/mL) cause destruction of protein & should be avoided as additives at these concentrations.
More General Terms
Additional Terms
References
- Henry, John Bernard, M.D., Clinical Diagnosis & Management by Laboratory Methods, 18th Edition, W.B. Saunders Company, Philadelphia, PA, 1991, pp.400-404.
- Teitz, Norbert W., Textbook of Clinical Chemistry, W.B. Saunders Company, Philadelphia, PA, 1986, pp.602-607.
- ACA IV Discrete Clinical Chemistry Analyzer Instrument Manual, Volume 3B, UP 49.
