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Subject: Protein (Total), Urine
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Normal urine contains up to 150 mg (1–14 mg/dL) of protein each day. This protein originates from ultrafiltration of plasma. Presence of increased amounts of proteins in urine is termed as proteinuria and is the first indication of renal disease. Proteinuria can be classified into three types:
Prerenal: overflow proteinuria, with an increase in plasma, low molecular weight proteins spill into urine (normal proteins, acute-phase reactants, light chain immunoglobulins)
Glomerular proteinuria: defective glomerular filtration barrier. This could be selective or nonselective to different proteins.
Tubular proteinuria: defective tubular reabsorption; increase in low molecular weight proteins.
Postrenal: proteins produced by the urinary tract, during inflammation, malignancy, or injury
Twenty-four–hour urine: <150 mg/day
Random urine: <200 mg/g creatinine
Evaluation of proteinuria (see Table 16.70) (e.g., following urinalysis in which proteinuria is detected)
Evaluation of renal diseases, including proteinuria complicating DM and the nephrotic syndromes.
Workup of other renal diseases, including malignant hypertension, GN, TTP, collagen diseases, toxemia of pregnancy, drug nephrotoxicity, hypersensitivity reactions, and allergic reactions and renal tubular lesions
Management of myeloma and evaluation of hypoproteinemia.
Guidelines for adults and children
Under most circumstances, untimed (spot) urine samples should be used to detect and monitor proteinuria in children and adults.
It is usually not necessary to obtain a timed urine collection (overnight or 24 h) for these evaluations in either children or adults.
First morning specimens are preferred, but random specimens are acceptable if first morning specimens are not available.
In most cases, screening with urine dipsticks is acceptable for detecting proteinuria:
Standard urine dipsticks are acceptable for detecting increased total urine protein.
Albumin-specific dipsticks are acceptable for detecting albuminuria.
Patients with a positive dipstick test (1+ or greater) should undergo confirmation of proteinuria by a quantitative measurement (protein-to-creatinine ratio or albumin-to-creatinine ratio) within 3 mo.
Patients with two or more positive quantitative tests temporally spaced by 1–2 wk should be diagnosed as having persistent proteinuria and undergo further evaluation and management for chronic kidney disease.
Monitoring proteinuria in patients with chronic kidney disease should be performed using quantitative measurements.
Specific guidelines for adults
When screening adults at increased risk for chronic kidney disease, albumin should be measured in a spot urine sample using either:
When monitoring proteinuria in adults with chronic kidney disease, the protein-to-creatinine ratio in spot urine samples should be measured using:
Total protein-to-creatinine ratio is acceptable if albumin-to-creatinine ratio is high (>500–1,000 mg/g)
Specific guidelines for children without diabetes
When screening children for chronic kidney disease, total urine protein should be measured in a spot urine sample using either
Standard urine dipstick
Total protein-to-creatinine ratio
Orthostatic proteinuria must be excluded by repeat measurement on a first morning specimen if the initial finding of proteinuria was obtained on a random specimen.
When monitoring proteinuria in children with chronic kidney disease, the total protein-to-creatinine ratio should be measured in spot urine specimens.
Specific guidelines for children with diabetes
Screening and monitoring of postpubertal children with diabetes of 5 or more years of duration should follow the guidelines for adults.
Screening and monitoring other children with diabetes should follow the guidelines for children without diabetes.
Data from: http://www.kidney.org/professionals/kdoqi/guidelines_ckd/p5_lab_g5.htm
Monoclonal gammopathies such as multiple myeloma and other myeloproliferative or lymphoproliferative disorders
Abnormal renal tubular absorption
Heavy metal poisoning
Sickle cell disease
Urinary tract malignancies
Inflammatory, degenerative, and irritative conditions of the lower urinary tract
Highly alkaline urine produces false-negative results.
Not reliable to quantify urinary immunoglobulin light chains.