Citrate, Urine

Diagnostic Use

One of the main functions of the kidney and urinary tract is to dispose of waste products and excess ions in a soluble form. Certain combinations of these ions, however are only sparingly soluble in urine and sometimes precipitate. The precipitates may become lodged in the urinary tract and form a nucleus around which a stone may grow (urolithiasis).

Most renal stones are passed spontaneously (65%). Those trapped in the kidney or lower urinary tract can cause serious anatomical damage, partial or total obstruction of urine flow, and excruciating pain for the patient. The estimated prevalence varies from about 1.5% of the general population in UK to 12% in USA6 and seems to depend on many factors including diet, climate, and genetic variability and underlying disease such as infection. A high intake of animal protein increases urinary excretion of calcium and oxalate, and the increase in purine consumption increases the excretion of uric acid. Incidence increases with ambient temperature mainly due to decreased urine volume. Diseases such as hyperparathyroidism and renal tubular acidosis (failure to acidify urine) can also lead to urolithiasis. Hospital admissions due to stone formation in New Zealand are 7.6 per 10,000 head of population.

Most stones are usually composed of calcium oxalate (58%) or calcium phosphate (14%) or a combination of these (9%) in Christchurch (refer to Woods et al poster in appendix). Others are due to infection with urea splitting bacteria (causes alkalization of urine and calcium phosphate and magnesium ammonium phosphate precipitation), excess uric acid (10%), or cystine (0.6%).

Low urinary citrate is subject to therapy by correcting acidosis, hypokalemia, or hypomagnesemia by altering diet or using drugs such as citrate and potassium.

Department

Lipids/Trace Metals

Delphic Registration Code

UCIT

Laboratory Handling

Separating

Take aliquot for UCRN please

Laboratory

Sample needs to be acidified to be acceptable for analysis. Please confirm pH is less than 4 before sending to CHL. Make sure 24 hour urine volume is provided on the form or sample.

Test Adds

Stable refrigerated for 14 days.

Turnaround Time

1 week

Test Code

4518

Specimen Type

• Urine

Specimen Requirements

Tube/Container Type:

Preferred

• 24hr Urine Container

Acceptable

• Pottle

Preferred Sample Volume (ml)

5

Minimum Sample Volume (ml)

2

No of Samples Required

1

Additional Specimen Information

24 hour collection into 2L bottle containing 10 mL HCL. Please confirm pH is less than 4 before sending to CHL for analysis.
Specimens not collected on acid are unsuitable for analysis and will not be processed.

Please note that this test "Citrate, urine" should be requested for patients with renal stones. For dialysis patients please see the "Citrate, plasma" listing.

Non-acidifed samples may give falsely low citrate due to bacterial decomposition and are not accepted for analysis.

Aliquot Instructions

Sample Type

• Urine

Minimum Volume (ml)

5

Transport to Lab

Frozen
If overnight - Frozen

Additional Referral/Aliquot Information

24 hour collection into 2L bottle containing 10 mL HCL. Please confirm pH is less than 4 before sending to CHL for analysis.

Specimens not collected on acid are unsuitable for analysis and will not be processed.

Interpretation

Urine Reference range:

CHL 0.3 – 3.8 mmol/ day n = 36

Published reference 0.4 – 3.4 mmol/ day n = 35

There may be an age related difference where older humans excrete slightly larger amounts of citrate however we have too few normal volunteers to demonstrate this in Christchurch.

Random urine reference range:

0-5 years >0.25 mol/mol creatinine

> 5 years >0.15 mol/mol creatinine

Reference Intervals

Reference range: 0.4 – 3.4 mmol/24 hours.

Test Method

Spectrophotometric / enzymatic

Non-Funded Test Cost

$84.47 (Exclusive of GST)

Billing Code

4518

Contact Information

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