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, sen-sitive method that primarily detects albumin in the urine. It is less sensitive for other forms of proteinuria.

Urinary protein:creatinine ratio (UP:UCr)

Collection of an 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 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 EMU UP:Ucr ratio. If the proteinuria is combined with haematuria, investigations should be directed at 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 centre for consideration for biopsy.