• Clinical science

Proteinuria

Abstract

Proteinuria is defined as a urinary protein excretion of > 150 mg/day. It has many possible causes, which may be benign (e.g., fever, intense exercise, dehydration) or more serious (e.g., glomerulonephritis, multiple myeloma). There are three different pathophysiological mechanisms that may lead to proteinuria: damage to the glomeruli (glomerular), damage to the tubules (tubular), or overproduction of low-molecular-weight proteins (overflow). If proteinuria is detected, patients should be further evaluated (e.g., additional urinalyses) to determine the underlying cause. The detection of microalbuminuria is of particular importance, as it suggests early diabetic or hypertensive nephropathy.

Definition

Proteinuria = urinary protein excretion of > 150 mg/day

References:[1]

Diagnosis

Urinalysis

Proteinuria can cause foamy urine!

Diagnosis of underlying disease

References:[2][1]

Classification

According to quantity

Microalbuminuria

  • Urine albumin excretion of 30–300 mg/day or 20–200 mcg/min
  • Diagnosis is made if two out of three tests are positive.
  • Early symptom of diabetic and hypertensive nephropathy
  • Specific urine dipstick tests; , radioimmunoassay, or ELISA required for detection

Overt proteinuria (formerly "macroalbuminuria")

According to origin

Glomerular proteinuria

Tubular proteinuria

  • Damage to the tubules → failure to reabsorb small proteins in the tubules → urinary protein excretion
  • The detection of beta-2 microglobulin without large proteins is typical.

Mixed proteinuria

Found in diseases that affect both the glomeruli and the tubules

Overflow proteinuria

Post-renal proteinuria

References:[3][1][4][5][6]

Benign proteinuria

  • Defined as isolated proteinuria < 3.5 g/day
  • Important, benign differential diagnosis in the evaluation of proteinuria
  • Very common; mostly affects younger individuals
  • Types of benign proteinuria
  • A dipstick test should be repeated to exclude underlying disease.
  • No treatment necessary; excellent prognosis

References:[1]

  • 1. Rovin BH. Assessment of urinary protein excretion and evaluation of isolated non-nephrotic proteinuria in adults. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/assessment-of-urinary-protein-excretion-and-evaluation-of-isolated-non-nephrotic-proteinuria-in-adults. Last updated January 25, 2017. Accessed April 20, 2017.
  • 2. Goldman L, Schafer AI. Goldman-Cecil Medicine, 25th Edition. Philadelphia, PA: Elsevier; 2016.
  • 3. Kumar V, Abbas AK, Aster JC. Robbins & Cotran Pathologic Basis of Disease. Philadelphia, PA: Elsevier Saunders; 2014.
  • 4. Devkota BP, Staros EB. Microalbumin. In: Microalbumin. New York, NY: WebMD. http://emedicine.medscape.com/article/2088184. Updated January 17, 2014. Accessed August 20, 2017.
  • 5. Kher K, Schnaper HW, Makker SP. Clinical Pediatric Nephrology. CRC Press; 2006.
  • 6. Swaminathan R. Handbook of Clinical Biochemistry. World Scientific; 2011.
  • Longo D, Fauci A, Kasper D, Hauser S, Jameson J, Loscalzo J. Harrisons's Principles of Internal Medicine, 18th Edition, 2011. McGraw-Hill Medical; 2011.
  • Herold G. Internal Medicine. Cologne, Germany: Herold G; 2014.
last updated 10/18/2018
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