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Urine Analysis | Urinary proteins (chemistry) , causes of Proteinuria

After illustrating the physical examination of urine sample, This article is to discuss the Chemical examination of urine, which includes:
 - Proteins .
- Glucose and ketones .
- Bilirubin and urobilinogen .
Glucose,  ketones, Bilirubin and urobilinogen will be discussed in another post , Here , we will focus on Urinary Proteins.

Urinary Proteins

• Normally, there is a trace of protein.
• It is a glycoprotein secreted by the cells of the ascending limb of the loop of Henle called (Tamm Horsfall) + trace of albumin, (normal urine protein = 150-200 mg/24 hr) .
• Slightly higher values up to 300 mg daily may be excreted by adolescents.

Causes of Proteinuria (Albuminuria)

1. Heavy proteinuria > 3.5gm/24 hr urine  = Nephrotic syndrome (glomerular Disease).
2. Mild proteinuria <  3.5gm :
- Nephritic syndrome.
- Tubulointerstitial disease.
- Orthostatic.
- Exercise.
- Febrile albumnuria.
- Excessive RBCs or pus cells may give False albuminuria.
- Congestive heart failure ==> Congested kidney ==> escape of protein through the glomerulus.

Methods of measurement of Proteinuria

1- Timed 24 hour urinary excretion.
2- Random urine samples in which albumin concentration is related to urinary creatinine concentration i.e. albumin/Cr ratio.
3- Dipsticks are available (Cannot detect Bence- Jones proteins)
N.B
• Normal urine contains albumin < 20 mg/L .
- Micro albuminuria = albumin between 20-150 mg/L this is an indicator of early diabetic nephropathy.
Proteinuria can be classified into :
-Glomerular e.g. glomerulopathies.
- Tubular e.g. Interstitial nephritis.
- Over flow e.g. multiple myeloma (Bence-Jones proteinuria), myoglobinuria.
-Hemodynamic e.g congestive heart failure, fever and exercise .
Read also :
Urine Analysis Physical examination,  interpretation and significance
- Urine analysis | Microscopic examination of urine sample, interpretation of results
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Tamer Mobarak

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