This post will cover what’s what on a urine dipstick and clarify what it means when “it lights up like a Christmas tree“
It’s 3 am and the 4-year-old with a fever has finally produced a urine sample. You dip it and it lights up “positive for everything”. You’re sure it’s positive for infection, but what if the pH is 5.5? What does it mean that there is blood and protein in it?
Surely white blood cells must mean an infection is present? If you have read the NICE UTI guidelines, so you know that is not necessarily the case.
The dipstick tests for leukocyte esterase. This is an enzyme produced by neutrophils and can be a sign of a urinary tract infection (white cells in urine = pyuria). These neutrophils, however, and the enzyme they produce can also be a sign of infection outside of the body such as vulvovaginitis. They may also be found in the presence of haematuria.
The overall sensitivity for leukocyte esterase is 49 – 79% with a specificity of 79 – 87%. As a result, it can be considered to be suggestive of “possible UTI”, and “probable UTI” if found with a positive nitrite sample (specificity increased to 99%).
What does this mean/bottom line: If positive and history suggestive (i.e. dysuria or fever) consider UTI and send for culture. If negative, then it is quite unlikely that there is an infection.
Nitrites are the breakdown product by gram-negative organisms such as E.coli. They are a more specific test (93-98%) than leukocytes but their sensitivity is lower (47-49%). The sensitivity is particularly poor as the urine needs to sit in the bladder for a while (at least 4 hours) for it to be positive.
What does this mean/bottom line: If it is positive, it is highly suggestive of infection. If it is negative, then does not necessarily rule out infection and needs correlation with leukocytes and presentation
Blood (haematuria) can be present for many reasons, so it is important to determine if it is microscopic (dipstick only) or macroscopic (visibly bloody). If blood is seen with leukocytes and/or nitrites then you should consider the child to have a UTI. If blood is seen with protein, then glomerulonephritis needs to be considered as a cause.
Causes of haematuria
- Kidney stones
- Renal tumour
- Menstruation (doesn’t cause haematuria but will show up on dipstick so don’t forget to ask)
Isolated microscopic haematuria is common and only needs investigation if persistent, but make sure blood pressure is checked as this is an often missed test. If haematuria is persistent it may need further investigation.
Reasons for further investigation
- Macroscopic haematuria
- High blood pressure
- Clinical oedema or features of fluid overload
- Persisting microscopic haematuria (>2 occasions over 2-4 weeks apart)
Bottom line: If just microscopic haematuria on dipstick without explanation, then request a repeat sample with GP in 2-4 weeks. Don’t forget to check a blood pressure!
The body excretes a small amount which is usually not enough to pick up on the dipstick.
If the body is “stressed” in illness or infection, it can cause proteinuria, however, it is also a sign of inflammation or damage within the kidney and so further history and examination is required.
When there is proteinuria of 2+ or more occurs during illness or a UTI, it can be repeated in a couple of weeks to ensure that it does not persist when the patient is well.
If there is no illness or infection, you would need to consider other causes such as glomerulonephritis and nephrotic syndrome, examine for oedema, and send off a protein : creatinine ratio sample.
Bottom line: small amounts can be seen in illness, but large amounts needs review depending on how the patient is.
This is not usually found in the urine, but small amounts can be detected if the patient is unwell, or is on steroids. If there is a large amount of glucose, consider checking blood glucose to rule out diabetes, and see if there is any other evidence of kidney problems.
A by-product from the breakdown of fat when sugar stores cannot be used. These can be seen in patients who have not been eating, vomiting and in DKA. It is always worth checking the blood glucose in these patients, as its absence in hypoglycaemic patients should alert you to a potential metabolic disorder.
Bottom line: Seen during periods of vomiting or not eating. Always check a blood glucose.
Excessive bilirubin that is not dealt with in the liver is excreted in the urine. Thus the presence of bilirubin in the urine can be seen in conjugated hyperbilirubinaemia, and therefore a feature of liver disease. If the urine dipstick measures urobilirubin then this can be seen normally on a dipstick (normal to 1+). A high urobilirubin could suggest haemolytic disease, as it reflects unconjugated bilirubin.
Bottom line: Bilirubin – not normal. Urobilinogen – normal (in small amounts)
This measures how dilute your urine is by comparing the solubility if the urine to water. If <1.005 then the urine is very dilute – do they drink a lot of water? If not the kidney may be unable to concentrate the urine, there it would be wise to consider checking serum sodium and assess the patient for features of diabetes insipidus.
High specific gravity means the urine is concentrated and suggests that the patient may be dehydrated. If they do not appear hydrated, then does the patient appear oedematous? This could suggest systemic disease
Bottom line: compare with the patient’s hydration status
The urine pH varies and is usually slightly acidic. It can be influenced by diet and medication. Usually, alkaline urine is a product of vegetarian diets and medication. It can also be present in UTIs caused by urea-splitting organisms, such as Proteus and Pseudomonas. It is seen in renal tubule anomalies or if the patient has metabolic alkalosis. Urinary acidosis is seen with high protein diets and can reflect systemic acidosis (for example, DKA, diarrhoea and vomiting)
Bottom line: Not very useful on its own.
Fernandes DJ, Jaidev M, Castelino DN. Utility of dipstick test (nitrite and leukocyte esterase) and microscopic analysis of urine when compared to culture in the diagnosis of urinary tract infection in children. Int J Contemp Pediatr 2017;5:156-60
Jeng-Daw Tsai, Chun-Chen Lin, Stephan S. Yang, Diagnosis of pediatric urinary tract infections, Urological Science, Volume 27, Issue 3, 2016, Pages 131-134