Calculi

Diagnostic Use

Stone analysis is used to determine the components of a renal stone and may be useful in determining the contributing cause(s).

See Additional Information below for links to documents related to testing, interpretation and management.

Interpretation

The following is a guide for the investigation of patients who have passed a renal stone:

A. Analysis of the Stone:

Send it to the laboratory. The composition of the stone may be helpful in identifying the cause of its formation.

B. Blood Tests: 5 mL blood in a heparin tube. Request the following tests:

• Na, K, Cl
• Urea, Creatinine
• Calcium, Phosphate
• Albumin
• Urate
• Parathyroid Hormone (PTH) if calcium is high or in patients with CKD
• Venous Bicarbonate
• Liver enzyme tests

C. Spot urine (mid-stream) is recommended:

• pH
• Microscopy for Red Cell Count, White Cell Count
• Microscopy for presence of crystals
• Urine culture
• Cystine

D. 24 hour urine tests are not usually necessary for a single stone episode, but should be done for recurrent stones.

Request the following tests:

• pH
• Volume
• Urea, Creatinine
• Sodium, Potassium, Calcium, Phosphate, Magnesium
• Oxalate, Citrate
• Urate

Preferred specimen is thymol-bottle which is available from LabPlus or LabTests Auckland (LTA)’s designated collection centres in the community.

Store at room temperature and deliver to LTA’s designated collection centres (or LabPlus Specimen Reception) within 6 hours of completion .

Collection requirements and contact details of LTA Collection Centres can be found by downloading the two attachments below – under Additional Information.

The Guide for interpreting 24 hour urinalysis for kidney stones: adults – under Additional Information.

NOTE: (Plain or HCl containing bottles may be used under occasional circumstances, but unable to deliver a full test repertoire – not recommended).

E. For children

Random urine samples are acceptable, if they are sent to the laboratory without delay. Acidification of the sample will be performed by the laboratory.

Please state “renal stone” on the form and request::

• Calcium, Oxalate
• Creatinine
• Urate
• Cystine
• Citrate
• pH

F.  If renal tubular acidosis is suspected, submit

a)  Venous or arterial blood taken in a heparinised blood gas syringe for:

• pH
• pCO2
• Bicarbonate

b) Random urine for pH and Ammonia.