Protein (Total), Urine

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Subject: Protein (Total), Urine

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Definition

  • 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)

    • Renal:

      • 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

  • Normal range:

    • Twenty-four–hour urine: <150 mg/day

    • Random urine: <200 mg/g creatinine

Use

  • 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.

 
TABLE 16–70
National Kidney Foundation Guidelines for Assessment of Proteinuria

Interpretation

Increased In

  • Nephrotic syndrome

  • Diabetic neuropathy

  • Monoclonal gammopathies such as multiple myeloma and other myeloproliferative or lymphoproliferative disorders

  • Abnormal renal tubular absorption

    • Fanconi syndrome

    • Heavy metal poisoning

    • Sickle cell disease

  • Urinary tract malignancies

  • Inflammatory, degenerative, and irritative conditions of the lower urinary tract

  • After exercise

Limitations

  • Highly alkaline urine produces false-negative results.

  • Not reliable to quantify urinary immunoglobulin light chains.

 
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