Proteinuria
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/m2/24 h or 4 mg/m2/h in children and 150 mg/24 h in adults).
- Nephrotic-range proteinuria >1,000 mg/m2/24 h 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 to 300 mg/g albumin/creatinine ratio or 30 to 300 mg/24 h); generally used to indicate kidney disease in those with diabetes mellitus
- Classification
- Persistent or fixed proteinuria
- Urinary dipstick ≥1+ on 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.
- May be associated with high fever, cold stress, dehydration, and exercise
- Orthostatic or postural proteinuria
- Elevated protein excretion when the patient is upright but normalizes when patient is supine
- The most common cause of fixed or transient proteinuria in childhood and adolescence
- Rarely exceeds 1 g/m2/24 h
- Benign condition and not associated with edema
- Persistent or fixed proteinuria
Epidemiology
Prevalence of asymptomatic proteinuria in school-aged children is 5.4–10.7% on single urine sample and <1% on ≥3 urine samples.
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
- 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/24 h and is not associated with edema
- The major marker is urinary β-2-microglobulin.
- 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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Citation
Cabana, Michael D., editor. "Proteinuria." 5-Minute Pediatric Consult, 8th ed., Wolters Kluwer, 2019. Pediatrics Central, peds.unboundmedicine.com/pedscentral/view/5-Minute-Pediatric-Consult/617415/1.0/Proteinuria.
Proteinuria. In: Cabana MDM, ed. 5-Minute Pediatric Consult. Wolters Kluwer; 2019. https://peds.unboundmedicine.com/pedscentral/view/5-Minute-Pediatric-Consult/617415/1.0/Proteinuria. Accessed August 31, 2024.
Proteinuria. (2019). In Cabana, M. D. (Ed.), 5-Minute Pediatric Consult (8th ed.). Wolters Kluwer. https://peds.unboundmedicine.com/pedscentral/view/5-Minute-Pediatric-Consult/617415/1.0/Proteinuria
Proteinuria [Internet]. In: Cabana MDM, editors. 5-Minute Pediatric Consult. Wolters Kluwer; 2019. [cited 2024 August 31]. Available from: https://peds.unboundmedicine.com/pedscentral/view/5-Minute-Pediatric-Consult/617415/1.0/Proteinuria.
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