Urine dipsticks

Cite this article as:
Laura Riddick. Urine dipsticks, Don't Forget the Bubbles, 2021. Available at:
https://doi.org/10.31440/DFTB.32596

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 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?

Leukocytes

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

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

Blood (haematuria) can be present for many reasons, so it is important to determine if there is microscopic (dipstick only) or macroscopic (visibly bloody). If blood is seen 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

  • Infection
  • Fever
  • Kidney stones
  • Glomerulonephritis
  • Renal tumour
  • Exercise
  • Trauma
  • 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 a 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
  • Proteinuria
  • 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!

Protein

The body excretes a small amount which is usually not enough to pick up on 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.

Glucose

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 a blood glucose to rule out diabetes, and see if there is any other evidence of kidney problems.

Ketones

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.

Bilirubin

Excessive bilirubin that is not dealt with in the liver is excreted in 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)

Specific Gravity

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 a serum sodium and assess the patient for features of diabetes insipidus.

A 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

A list of causes of high specific gravity

Bottom line: compare to the patient’s hydration status

pH

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.

Urine dipticks infographics

Selected references

https://litfl.com/dipstick-urinalysis/

https://patient.info/treatment-medication/urine-dipstick-test

Yates A. Urinalysis: how to interpret results. Nursing Times. 2016 Jun 8;112(2):1-3.

https://geekymedics.com/urinalysis-osce-guide/

https://www.mayoclinic.org/tests-procedures/urinalysis/about/pac-20384907

https://www.nice.org.uk/guidance/cg54/chapter/Recommendations#diagnosis

https://www.clinicalguidelines.scot.nhs.uk/nhsggc-paediatric-clinical-guidelines/nhsggc-guidelines/emergency-medicine/haematuria-management-and-investigation-in-paediatrics/

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

Tsai JD, Lin CC, Yang SS. Diagnosis of pediatric urinary tract infections. Urological Science. 2016 Sep 1;27(3):131-4.

Urine collection

Cite this article as:
Andrew Tagg. Urine collection, Don't Forget the Bubbles, 2017. Available at:
https://doi.org/10.31440/DFTB.10888

Urine, the other amber nectar, is something we seem to want to check in nearly every unwell appearing child.  But what do you do if they just don’t want to go?  You’ve filled them up with icy poles or dilute apple juice and you are just waiting for a sample to be produced.  As a doctor (and as a parent) I have been urinated on (by children) more times than I dare to recall (in fact it happened to me just this morning) but how do we make sure we get a sample when we need it? With 4 hour targets to meet it’s worth considering any means of speeding up the process.

Paediatric Blunt Trauma and Microhaematuria

Cite this article as:
Taylan Gurgenci. Paediatric Blunt Trauma and Microhaematuria, Don't Forget the Bubbles, 2016. Available at:
https://doi.org/10.31440/DFTB.8785

Bottom line pearls:

  • Gross haematuria must be taken seriously as it raises the likelihood of finding significant renal pathology
  • Microhaematuria of any degree is most useful when serial urinalyses are performed.  Seeing a downward trend in the degree of microhaematuria is much more useful than the actual number.
  • The received wisdom suggesting a microhaematuria of 50RBC/HPF is the dividing line between trivial and significant haematuria is not supported by much evidence.
  • Microhaematuria in a child with a possible renal injury is best managed by serial examination, serial FBC, and serial urinalysis.  Discharge is safe if the examination remains stable, the FBC is stable, and the microhaematuria resolves.
  • There is no role for the urine dipstick in suspected renal injury.
  • Adult imaging protocols may be applied to paediatric blunt trauma though with some important provisos.

Microscopic haematuria

Cite this article as:
Ben Lawton. Microscopic haematuria, Don't Forget the Bubbles, 2013. Available at:
https://doi.org/10.31440/DFTB.2916

A previously well 3-year-old girl presented to your ED with a history of fever. You have confidently diagnosed otitis media and are just about to discharge the child when the nurse mentions a urine was requested at triage and has come back positive for blood.

The nurse asks you what it means if the girl has blood in her urine….

The Bottom Line

  • With a urine dipstick that is positive for blood, the first thing to do is establish whether the finding is real (by microscopy).
  • Remember to look for UTI, hypertension, proteinuria and concerning family history
  • In the absence of red flags on history and examination, no investigations beyond microscopy are required until the microscopic haematuria has proved to be persistent.

What does this finding represent?

Microscopic haematuria is a common finding in the setting of febrile illness. It can be caused by many benign phenomena including adenovirus, ibuprofen, antibiotics including penicillin and indeed by fever itself.

There is always a concern that haematuria represents significant underlying renal pathology but in this circumstance, the risk is extremely small.

What further assessment should you perform and what are you looking for?

Clinical examination and urine microscopy are sufficient at this stage. The following table outlines the major things you should be looking for. There are more sensitive and specific ways of searching for all these findings but in this context, underlying renal disease is pretty unlikely so clinical assessment alone is good enough for now.

The key things to remember are to check for hypertension, proteinuria, UTI and a family history of renal failure.

FindingSuggestive of
Failure to thrivechronic disease process
WTU for proteinglomerulonephritis
WTU for leucs/nitriteUTI
FH renal failureany hereditary nephropathy
FH deafnessAlport syndrome
FH renal stonesfamilial hypercalciuria
Hx infection (2 weeks ago)post strep GN
Hx infection (1-2 days ago)TBMN/IgA nephropathy
bruises/bleedingbleeding diathesis
loin massesWilm’s tumour
oedemanephrotic syndrome
hypertensionnephritis

If this is all normal the only investigation required at this stage is urine microscopy and culture to confirm and quantify the presence of blood and determine if the cells are dysmorphic (suggesting a glomerular source of bleeding), This is also the definitive test for a UTI.

Any positive findings from the list above should prompt more sensitive/specific investigation.

 

So the history, exam and urine microscopy was normal, can I forget about the haematuria?

No, although significant renal disease is unlikely the child should be referred back to their GP for a repeat urinalysis in 2-4 weeks when they are well. If the haematuria has resolved at that time then no further action is required. Persistent haematuria will require further investigation.

 

So what proportion of kids with microscopic haematuria actually have significant renal disease?

A large study where urinalysis was performed in asymptomatic school children to evaluate its suitability as a screening tool for occult renal disease found the following:

  • Children screened – 7 million
  • Abnormal UA – 1044
  • Isolated haematuria – 719 (of 1044)
  • Biopsy performed (indications for biopsy = severe proteinuria, hypertension, abnormal renal function of a family history of renal disease) – 52
  • Thin glomerular basement membrane nephropathy (benign condition) on biopsy – 33
  • Other defined pathology on biopsy – 16

In other words of 719 children with isolated haematuria, 16 went on to have proven renal disease that warranted further management.

This was a population of well children and you can imagine that in a population of febrile kids, with the benign reasons for having haematuria outlined above, the proportion of kids with significant renal disease as a cause of their microscopic haematuria would be even smaller.

 

Does a positive dipstick mean there is definitely blood in the urine?

No, false positives on a dipstick can result from haemoglobinuria (e.g secondary to haemolysis) or myoglobinuria. It is also worth remembering that blood in the urine may originate from the vagina or rectum and some causes (e.g. anal fissure) may not be immediately evident on exam). Several things have been reported to cause a red tinge to the urine that may be mistaken for blood.

The following can all cause the appearance of gross haematuria but they should not cause a dipstick to read positive:

  • Drugs – chloroquine, ibuprofen, iron, sorbitol, nitrofurantoin, phenazopyridine, phenolphthalein
    Foods – beets, blackberries, food colouring metabolites
    Other – bile pigments, homogentisic acid, melanin, methemoglobin, porphyrin, tyrosine, urates

Microscopy should be able to confirm that the blood is for real.

 

References

McTaggart S. Childhood Urinary Conditions. Aust Fam Phys 2005; 34:937-41.

Park YH, Choi JY, Chung HS, et al. Hematuria and proteinuria in a mass school urine screening test. Pediatr Nephrol 2005; 20:1126–1130.

Quigley R. Evaluation of hematuria and proteinuria: how should a pediatrician proceed? Current Opinion in Pediatrics 2008, 20:140–144.

Rees L, et al. Oxford Specialist Handbooks in Paediatrics: Paediatric Nephrology, Oxford University Press. 2007. p18-19.