Information
Editors
Interpretation of Urine Test Results in Children
Essentials
- Urinalysis is a first line investigation whenever a urinary tract infection (UTI), kidney disease or metabolic disease is suspected. A chemical examination of urine (reagent strip or dipstick test) and urine particle analysis are the baseline tests. A diagnosis of a UTI also requires a bacterial culture of the urine.
- Reagent strip tests are good for screening purposes, but abnormal findings must be verified with further investigations, such as particle analysis or a quantitative protein measurement.
- In order to obtain a reliable result, urine samples from children should be collected in a hospital or health centre. Urine may be collected at home if the reagent strip testing is to be carried out at home.
Indication for routine urinalysis
- History
- Urinary frequency
- Excessive drinking
- Pain or burning on urination
- Foamy urine
- Abnormal colour or smell of urine
- Findings
- Findings suggestive of kidney disease, such as increased plasma creatinine concentration
- Oedema (occasionally only affects the eyelids)
- Hypertension
- Petechiae without sepsis
- Unexplained recurrent febrile episodes in an infant
Abnormal urine test results
- Abnormal appearance and smell
- A red-brown colour is not only a sign of haematuria but may also indicate concentrated urine, consumption of certain foods or medicines, or hyperbilirubinaemia.
- Excessively foamy urine may be caused by proteinuria.
- An unpleasant smell is only rarely an indication of a UTI.
- In the above situations, a chemical urinalysis is an adequate baseline test. If necessary, further investigations should be ordered according to the results of the reagent strip test and clinical findings.
- Proteinuria
- Proteinuria may be caused by glomerular dysfunction, where the urinary excretion of albumin is increased, or by tubular dysfunction, where the excretion of proteins involves low molecular weight proteins, such as beta-2-microglobulin or alpha-1-microglobulin.
- Reagent strip tests mainly detect the presence of albumin in the urine. A positive result (≥ ++) must be verified by quantitative measurement.
- Normal urinary excretion of protein is less than 100 mg in 24 hours. The amount of protein is compared to the creatinine concentration in a random spot sample, the upper limit of normal being 20 mg/mmol in over 2 year olds and 50 mg/mmol in under 2 year olds. Nephrotic-range proteinuria refers to excretion of more than 1 500 mg of protein in 24 hours or a protein excretion that exceeds 200 mg/mmol in a random sample.
- Proteinuria may also be physiological, caused by physical exertion or fever. Orthostatic proteinuria is also harmless. In these situations, the amount of protein in urine is usually less than 1 g in 24 hours (< +++).
- Nephrotic-range proteinuria may cause hypoalbuminaemia and oedema. Nephropathy may be associated not only with nephrotic syndrome (= minimal change disease) but also with glomerulonephritis.
- If the concentration of urinary protein is less than 1.5 g/l (< +++) and the child has no nephritic symptoms (oedema, hypertension, oliguria), the urine sample may be rechecked within one week (e.g. after the child has recovered from a febrile illness). Persistent proteinuria is an indication for a non-urgent referral to a paediatrician.
- In order to exclude orthostatic proteinuria, a morning urine sample may be collected at home before the child gets out of bed in the morning.
- Proteinuria above 1.5 g/l (≥ +++) necessitates a consultation with a paediatrician and, as required, an emergency referral to a paediatrician.
- Haematuria
- Microscopic haematuria is present if particle analysis shows ≥ 3 red blood cells/high power field (microscope) or ≥ 20 × 106 red blood cells/l (flow cytometry).
- The incidence of haematuria in children is 4%, and significant kidney disease is diagnosed in less than 10% of these cases.
- Haematuria may be caused by kidney disease, mucosal bleeding from the urinary tract (ureters, bladder or urethra) or mucosal or skin damage to the genital area.
- The evaluation of haematuria should encompass the following: a careful history (e.g. past history of infections, family history of kidney disease, urinary calculus), physical examination, including an inspection of the skin (petechiae, cutaneous infections, oedema), palpation of the abdomen and an external examination of the genital area.
- In asymptomatic microscopic haematuria, three new samples should be checked at weekly intervals. If marked microscopic haematuria is detected in all repeat samples, a non-urgent referral to a paediatrician may be indicated.
- Symptomatic microscopic haematuria (oedema, hypertension or decreased urine output), or haematuria with concurrent proteinuria (> 1.5 g/l), is an indication for an urgent referral to a paediatrician.
- The first occurrence of macroscopic haematuria is an indication for an urgent referral to a paediatrician.
- Pyuria
- Normal urinary excretion of white blood cells does not exceed 10 × 106 /l, which corresponds to 2 white blood cells/high power field (microscope).
- The most common cause of pyuria is a UTI. Other causes may include tubulo-interstitial nephritis, glomerulonephritis and interstitial cystitis.
- Bacteriuria: see Urinary Tract Infection in a Child
- Other findings
- Tubular cells indicate kidney damage (pyelonephritis, tubulo-interstitial nephritis, acute tubular necrosis).
- Transitional epithelial cells are derived from the urinary tract (anywhere from the renal pelvis to the bladder/base of the urethra). Their appearance in urine is indicative of damage to the urinary tract (cystitis-pyelitis, urinary calculus, malignancy).
- Squamous epithelial cells originate from the urethra or the external genital organs. Their appearance in urine does not indicate kidney disease.
- The only urinary casts normally present in urine are hyaline casts (= Tamm-Horsfall protein). Granular or waxy casts (derived from plasma proteins) and fatty casts (derived from plasma lipids) are indicative of kidney disease.