Tag Archives: urinalysis

June 2019 newsletter

Possible causes of macrocephaly this month.  Also the start of a new series on causes of coca-cola coloured urine and updates on safeguarding CPD requirements and the terminology of children “in care”.  Do leave comments below:

March 2019 PDF published

Part 2 of Medically Unexplained Symptoms this month.  Also antibiotics in cystitis, too many investigations in community acquired pneumonia, carotenaemia and heart murmurs in unwell children.  Do leave comments below:

November 2017 PDF

Children’s cancer information this month – prevalence and red flags, a link to the excellent immunisation resource – Oxford vaccine group – for all those questions about individual immunisations that you can’t always answer,  NICE’s recent UTI update and infant dyschezia.  Do leave comments below.

October 2017 PDF digest

Local anaesthetic cream this month (why do some places not use it in the under 1’s?), a link to useful “flash card” learning in the paediatric ED from Leicester, new Movicol doses, diphtheria and the last instalment of urinalysis with bilirubin and urobilinogen.  A reminder also to please discuss children with glycosuria and a high BM with a paediatrician – most children have type 1 diabetes and are at risk of DKA at diagnosis.  Do leave comments below:

September 2107 PDF ready to go

A bit more on babies’ stooling habits this month, NICE’s update on the epilepsies and glycosuria.  Also the annual round up of useful blogs to get newcomers off to a good start in their paediatric practice.  Please do leave comments below:

Urinalysis – What Each Component Means

www.lifeinthefastlane.com has a great article describing the components of the humble urine dipstick and what we might learn from it. It is available here and I am going to borrow extensively from Dr Mike Cadogan’s work over the next few months but try to put a paediatric slant on it.

1) SPECIFIC GRAVITY (SG) – measures concentration of urine

Normal range varies by lab but roughly 1.005 to 1.030
< 1.005 – diabetes insipidus, fluid overload, pyelonephritis
> 1.030 – dehydration, glycosuria, SIADH
Falsely high in proteinuria, falsely low in alkaline urine

2) pH

Glomerular filtrate has a pH of about 7.4 which is acidified to about 6 by the time it is passed as urine.

Causes of alkaline urine (⇑pH)
Causes of acidic urine (⇓pH)
Old sample, vegetarian diet, salicylate
overdose, UTI, citrus fruit ++, low carb diet
Metabolic/respiratory acidosis, diarrhoea, high
protein diet, DKA, cranberries, malabsorption
Not a helpful test as can vary from 4.5 to 8.  Stones can form with either alkaline or acidic urine

3) NITRITES

Nitrites on a dipstick test has a positive predictive value of 96% ie. it is highly likely that the child has a UTI. But the test’s negative predictive value is not so good (around 70%) ie. some children still have a UTI even though they have no nitrites in their urine. Why?

  • ? only gram -ive bacteria convert nitrates to nitrites in urine; E coli, Proteus and Klebsiella are gram -ive, Enterococcus is not
  • Can take 4 hours for this conversion to take place. Babies don’t hold urine in their bladder for that long.

The current NICE UTI guideline recommends microscopy and culture to rule out UTI in children younger than 3 but suggests that dipstick urinalysis is enough in older children. They are currently looking at new evidence to see if the dipstick result (leucocytes and nitrites) can be “trusted” in younger children. Update due to be published this year.

4) LEUCOCYTES

  • Determines the presence of whole or lysed white cells in the urine (pyuria) by detecting leucocyte esterase activity.
  • A positive leucocyte esterase test correlates well with pyuria. BUT, pyuria does not necessarily indicate a UTI. The white cells may be increased because of infection elsewhere. NICE “do not do recommendation”: Do not test urine if the infant or child has an obvious alternative source of infection.
  • Conversely, a UTI diagnosis may be missed if a negative urinalysis dipstick is used to exclude UTI. Especially true in children less than 3 years old. NICE recommendation: if you suspect a UTI clinically, send urine for MC&S and do not rely on the dipstick result alone; we are supposed to diagnose a UTI if there is bacteriuria on microscopy, even without pyuria. Click here for further information on diagnosing UTI in children; it’s not quite as straight forward as you would hope.

5) BLOOD

  • Red or brown urine does not always mean blood
  • High false positive rate (eg. haemoglobinuria, myoglobinuria, concentrated urine, menstrual blood in the urine sample, rigorous exercise) so dipstick positive blood needs to be looked at under the microscope to accurately diagnose haematuria
  • False negative possible if specific gravity is < 1007
  • Significant haematuria is defined as ≥ 10 red blood cells (≥ 3 in adults) per high-power field in a properly collected and centrifuged urine specimen
  • Isolated microscopic haematuria in a well child only really needs further investigation after 3 positive samples over a period of a few months
  • Concomitant proteinuria, high BP or a palpable abdominal mass should be investigated promptly
  • Possible causes of haematuria in children:
    • UTI
    • Viral infections
    • Post streptococcal glomerulonephritis
    • Trauma
    • Henoch Schonlein Purpura
    • Wilm’s tumour (median age 3.5 years)
  • The Royal Children’s Hospital in Melbourne has a sensible, easy-to-follow guideline for the management of children with haematuria

6) PROTEIN

  • Normal daily protein excretion ≤ 150mg/24 hours or 10mg/100mL. In nephrotic syndrome >3.5g/day is excreted. “Trace” positive results = 10 mg/100 ml or about 150 mg/24 hours (the upper limit of normal).
  • Causes: transient or orthostatic (most common and benign), click here for summary of causes in children
  • False Positive: Concentrated or alkaline urine (pH >7.5), trace residue of bleach, NaHCO3, cephalosporins
  • False Negative: Dilute urine or acidic urine (pH <5)  Use spot, early morning urine testing for a protein/creatinine ratio if the urine dipstick test result is 1+ protein or more. A 24 hour collection is impractical
Dipstick protein reading Protein excretion gm/24 hours Protein excretion mg/dL
Negative <0.1 <10
Trace 0.1-0.2 15
1+ (and above is abnormal) 0.2-0.5 30
2+ 0.5-1.5 100
 3+ 2.0-5.0 300
4+ >5.0 >1000

7) KETONES

Ketones are not normally found in the urine. Produced by the liver as intermediate products of fatty acid metabolism, in normal states they will be completely metabolised. In “starvation” states eg. DKA or vomiting and reduced intake, fever, extreme cold and extreme exercise, the body metabolises increased fat to get the energy it needs to keep functioning. This results in ketonuria. ≥ ++ is abnormal.  We often see ketones in the urine of unwell children in the ED. When glucose is present at the same time in the urine, diabetic ketoacidosis is the likely diagnosis.

RESOURCES

http://lifeinthefastlane.com/investigations/urinalysis/
http://labtestsonline.org.uk/understanding/analytes/urinalysis/ui-exams?start=1
https://patient.info/doctor/urine-ketones-meanings-and-false-positives-pro

August 2017 PDF is published

Ambulatory Blood Pressure Monitoring this month, re-housed NSPCC leaflets, ketonuria and lignocaine in intraosseous fluids and fluid intake in constipated children.  Do leave comments below.

July 2017 PDF

Proteinuria this month, babies’ poo, bedwetting and a bit more on paediatric hypertension.  Please do leave comments below.

June 2017 PDF

Haematuria this month with links to an algorithmic Australian guideline on how to manage it in children, assessing paediatric hypertension, postural orthostatic tachycardia syndrome and the last for the time being in the “decoding the FBC” series – MCHC.

Please do leave comments below:

URINALYSIS

(From June 2017 Paediatric Pearls Newsletter)

Also see:

Blood

  • Red or brown urine does not always mean blood
  • High false positive rate (eg. haemoglobinuria, myoglobinuria, concentrated urine, menstrual blood in the urine sample, rigorous exercise) so dipstick positive blood needs to be looked at under the microscope to accurately diagnose haematuria
  • False negative possible if specific gravity is < 1007
  • Significant haematuria is defined as ≥ 10 red blood cells (≥ 3 in adults) per high-power field in a properly collected and centrifuged urine specimen
  • Isolated microscopic haematuria in a well child only really needs further investigation after 3 positive samples over a period of a few months
  • Concomitant proteinuria, high BP or a palpable abdominal mass should be investigated promptly
  • Possible causes of haematuria in children:
    • UTI
    • Viral infections
    • Post streptococcal glomerulonephritis
    • Trauma
    • Henoch Schonlein Purpura
    • Wilm’s tumour (median age 3.5 years)

Resources: