Specimen Collection
Adults:
24 hr urine collected into a thymol container and delivered to a collection centre within 6 hours of completion to allow prompt acidification. If this is not possible, the specimen can be collected into acid (20ml of 6M HCL)
Testing citrate on spot urine is reserved for children <15 yrs. Those who are >=15 yrs old should always aim for a 24 hour urine collect. If there are unique clinical circumstances whereby only a casual urine can be collected, then prior approval must be obtained from the on-duty Chemical Pathologist.
Children:
Random urine samples may be used; collect into a plain container and transport into the laboratory for acidification within 6 hours. If there will be a delay in transport to the laboratory, please freeze the sample and transport frozen.
Reference Intervals
Uncertainty of measurement: 10%
Adult
|
|
24h urine (mmol/day)
|
|
Male
|
> 1.9
|
|
|
Female
|
> 1.6
|
|
For patients with a history of renal stones, the therapeutic target excretion greater than 2.0 mmol/day is recommended.
Children
under 16 years old*
(
1
)
1.
24h urine
Boys:
> 1.9
mmol/1.73m2/day
Girls:
> 1.6
mmol/1.73m2/day
*As the cut offs are based on BSA, they are reported as "comment" with the result.
2. Spot urine
|
|
Spot urine (mmol/mmol)
|
|
0 - 5 years
|
> 0.25
|
|
6 - 15 years
|
> 0.15
|
Conversion factor: mg/24h x 0.00522 = mmol/24h
References
1.
Hoppe B, Kemper MJ. Diagnostic examination of the child with urolithiasis or nephrocalcinosis. Pediatr Nephrol. 2010;25(3):403-13.
Turnaround Time: Within 2 weeks
Assay Method
Principle:
End point colourimetric
Reagent:
R-Biopharm
Analyser:
Indiko Plus
Diagnostic Use and Interpretation
24h urine citrate measurement is indicated for investigation of patients with calcium renal stones and to monitor patients' response to therapy.
Urinary citrate acts as an inhibitor for calcium oxalate stone formation and low urine citrate excretion is a known risk factor for kidney stone formation. Urinary citrate binds to urinary calcium, forming a soluble complex and decreasing available free ionic calcium for calcium oxalate stone formation. Urinary citrate interacts with calcium oxalate crystal as an inhibitor of crystal aggregation and crystal growth.(2)
Literature shows a large prevalence of hypocitraturia in stone forming patients (20-60%).
Although the majority of patients have idiopathic hypocitraturia, c
auses of hypocitraturia include renal tubular acidosis, metabolic acidosis, hypokalaemia, diet (animal protein, high sodium intake, low fruit/vegetable intake), medications (ACE inhibitors, acetazolamide, amiloride, calcium, lithium, vitamin D), hypocalciuria, hypomagenesuria, and renal insufficiency. Management of hypocitraturia would involve a combination of dietary modification and oral akali (e.g. potassium citrate, sodium citrate), which will increase urinary citrate by providing an alkali load.(3) For patients with a history of renal stones, the therapeutic target excretion greater than 2.0 mmol/day is recommended.
1. Hoppe B, Kemper MJ. Diagnostic examination of the child with urolithiasis or nephrocalcinosis. Pediatr Nephrol. 2010;25(3):403-13.
2. Domrongkitchaiporn S, Stitchantrakul W, Kochakarn W. Causes of hypocitraturia in recurrent calcium stone formers: focusing on urinary potassium excretion. Am J Kidney Dis. 2006;48(4):546-54.
3. Zuckerman JM, Assimos DG. Hypocitraturia: pathophysiology and medical management. Rev Urol. 2009;11(3):134-44.
Contact Information
Emails to
chemicalpathologist@adhb.govt.nz
will receive priority attention from the on-call chemical pathologist.
If the query concerns a specific patient please include the NHI number in your email.
If email is not a suitable option, please contact the on-call chemical pathologist via
Lablink (Auckland City Hospital ext. 22000 or 09-3078995).
Individual chemical pathologists may be contacted but will not be available at all times.
After-hours
: contact
Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours.
Dr Samarina Musaad
(Clinical Lead)
:
SamarinaM@adhb.govt.nz
ext. 22402
Dr Cam Kyle:
CampbellK@adhb.govt.nz
ext 22052
Dr Weldon Chiu:
WeldonC@adhb.govt.nz
ext. 23427
Dr Campbell Heron:
CHeron@adhb.govt.nz
ext. 23427
Dr Sakunthala Jayasinghe:
Sakunthala@adhb.govt.nz
ext. 23427
Specimen Transport Instructions for Referring Laboratories
For
all samples, take a 10ml aliquot and acidify with concentrated HCL to pH 2
within 6 hours of receipt. Send frozen.