Paediatrics: Proteinuria

Proteinuria

This is defined as excessive urinary protein excretion. Protein may be found in the urine of healthy children and does not exceed 0.15g/24hr.

Detection of proteinuria

Urinalysis

Performed by dipstick testing (Table 11.1), this is a cheap, practicable, sensitive method that primarily detects albumin in the urine. It is less sensitive to other forms of proteinuria.

Urinary protein: creatinine ratio (UP: UCr)

Collection of early morning urine (EMU) specimen for measurement of the urinary protein to creatinine ratio. Normal <20mg/mmol

24hr urinary protein excretion

This is the gold standard test and requires a 24hr collection of urine to estimate urinary protein excretion.

• Normal: <30mg/24hr.
• Microalbuminuria: 30–300mg/24hr.
• Proteinuria: >300mg/24hr.

Causes

 Proteinuria may be due to benign or pathological causes.

Non-pathological proteinuria

• Transient.
• Fever.
• Exercise.
• Urinary tract infection (UTI).
• Orthostatic proteinuria (postural proteinuria). This is a common cause of referral in older children. There is usually no history of significance and a normal examination. Investigations reveal a normal UP:UCr ratio in early morning urine with an elevated level in afternoon specimen (may require two 12hr collections). This is regarded as a benign finding and requires no treatment.

Pathological (persistent) proteinuria

This may be seen in a number of renal disorders including:

• Nephrotic syndrome;
• Glomerulonephritis;
• Chronic kidney disease;
• Tubular interstitial nephritis.

Investigations

Proteinuria detected on dipstick testing should be confirmed using the EMU UP: Ucr ratio. If the proteinuria is combined with haematuria, investigations should be directed at the causes of haematuria and nephritis.

• A renal US scan should also be performed.
• Patients with persistent proteinuria detected over a period of 6–12mths should be referred to a paediatric nephrology center for consideration for biopsy.