Proteinuria

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Basics

Description

  • Protein may be found in the urine of healthy children.
  • The term proteinuria is used to indicate urinary protein excretion beyond the upper limit of normal (100 mg/m2/day or 4 mg/m2/h in children and 150 mg/day in adults).
    • Nephrotic range proteinuria >1,000 mg/m2/day or 40 mg/m2/h
    • Nephrotic syndrome: nephrotic-range proteinuria with edema and hypoalbuminemia (<2.5 g/dL)
    • Microalbuminuria: elevated urinary excretion of albumin (30–300 mg/g albumin/creatinine ratio or 30–300 mg/day). Currently, it is only used to indicate kidney disease in those with diabetes mellitus.
  • Classification
    • Persistent or fixed proteinuria
      • Urinary dipstick ≥1+ in the first morning urine specimen on ≥3 samples >1 week apart
      • Requires prompt referral to nephrology
    • Transient proteinuria
      • Proteinuria absent on subsequent urine examinations
      • It is not usually associated with clinically significant underlying renal disease.
      • Often associated with high fever, cold stress, dehydration, and exercise
    • Orthostatic or postural proteinuria
      • Elevated protein excretion when the patient is upright that normalizes when patient is supine
      • The most common cause of fixed or transient proteinuria in childhood and adolescence
      • Proteinuria rarely exceeds 1 g/m2/day.
      • Benign condition

Pathophysiology

  • Normally, ∼50% urinary proteins are derived from tissue proteins and proteins from cells lining the urinary tract (i.e., Tamm-Horsfall protein).
  • Proteinuria may be the result of glomerular proteinuria or tubular proteinuria.
  • Glomerular proteinuria
    • An increased permeability of the glomeruli to the passage of plasma proteins
    • Normally may range from <1 to >30 mg/day
    • Large amounts of glomerular proteinuria may be found in the context of edema and hypoalbuminemia (nephrotic syndrome).
    • If there is hypertension, abnormal glomerular filtration rate, and hematuria, there may be nephritis as well.
  • Tubular proteinuria
    • Decreased reabsorption of low-molecular-weight proteins by the proximal renal tubules
    • Rarely >1 g/day and is not associated with edema.
    • The major marker is urinary beta-2-microglobulin.
    • It may be associated with other defects of proximal tubular function (e.g., renal tubular acidosis [RTA], glucosuria, phosphaturia, aminoaciduria) and tubular interstitial processes.

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Basics

Description

  • Protein may be found in the urine of healthy children.
  • The term proteinuria is used to indicate urinary protein excretion beyond the upper limit of normal (100 mg/m2/day or 4 mg/m2/h in children and 150 mg/day in adults).
    • Nephrotic range proteinuria >1,000 mg/m2/day or 40 mg/m2/h
    • Nephrotic syndrome: nephrotic-range proteinuria with edema and hypoalbuminemia (<2.5 g/dL)
    • Microalbuminuria: elevated urinary excretion of albumin (30–300 mg/g albumin/creatinine ratio or 30–300 mg/day). Currently, it is only used to indicate kidney disease in those with diabetes mellitus.
  • Classification
    • Persistent or fixed proteinuria
      • Urinary dipstick ≥1+ in the first morning urine specimen on ≥3 samples >1 week apart
      • Requires prompt referral to nephrology
    • Transient proteinuria
      • Proteinuria absent on subsequent urine examinations
      • It is not usually associated with clinically significant underlying renal disease.
      • Often associated with high fever, cold stress, dehydration, and exercise
    • Orthostatic or postural proteinuria
      • Elevated protein excretion when the patient is upright that normalizes when patient is supine
      • The most common cause of fixed or transient proteinuria in childhood and adolescence
      • Proteinuria rarely exceeds 1 g/m2/day.
      • Benign condition

Pathophysiology

  • Normally, ∼50% urinary proteins are derived from tissue proteins and proteins from cells lining the urinary tract (i.e., Tamm-Horsfall protein).
  • Proteinuria may be the result of glomerular proteinuria or tubular proteinuria.
  • Glomerular proteinuria
    • An increased permeability of the glomeruli to the passage of plasma proteins
    • Normally may range from <1 to >30 mg/day
    • Large amounts of glomerular proteinuria may be found in the context of edema and hypoalbuminemia (nephrotic syndrome).
    • If there is hypertension, abnormal glomerular filtration rate, and hematuria, there may be nephritis as well.
  • Tubular proteinuria
    • Decreased reabsorption of low-molecular-weight proteins by the proximal renal tubules
    • Rarely >1 g/day and is not associated with edema.
    • The major marker is urinary beta-2-microglobulin.
    • It may be associated with other defects of proximal tubular function (e.g., renal tubular acidosis [RTA], glucosuria, phosphaturia, aminoaciduria) and tubular interstitial processes.

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