Clinical use: Tests of urine will show if the individual is excreting too many stone-forming minerals or too few stone-inhibiting substances.
Background: Kidney stones often have no definite, single cause. A number of factors, often in combination, create the conditions in which susceptible people develop kidney stones. Kidney stones form when the components of urine, fluid and various minerals and acids are out of balance. When this happens, urine contains more crystal-forming substances, such as calcium, oxalate and uric acid, than the available fluid can dilute. At the same time, urine may have low concentration of substances that inhibit crystal formation e.g citrate. This creates an environment in which kidney stones are more likely to form. Most kidney stones contain crystals of more than one type.

Types of kidney stones include:
Calcium stones, most kidney stones are calcium stones, usually in the form of calcium oxalate;
Struvite stones (Magnesium Ammonium Phosphate) stones form in response to an infection, such as a urinary tract infection. Struvite stones can grow quickly and become quite large.
Uric acid stones can form in people who are dehydrated, those who eat a high-protein diet and those with gout. Certain genetic factors and disorders of the blood-producing tissues also may predispose an individual to uric acid stones.

Cystine stones, these stones represent only a small percentage of kidney stones. They form in people with a hereditary disorder that causes the kidneys to excrete excessive amounts of certain amino acids (cystinuria).
Other stones. Other, rarer types of kidney stones e.g. xanthine can occur.

Reference ranges:
Urine Citrate: Male: 0.6 – 4.8 mmol/24h
Female: 1.3 – 6.0 mmol/24h
Urine Cystine: 0.0 – 186 umol/24h
Urine Oxalate: 100 – 460 umol/24h
Associated diseases:
Patient preparation:
Specimen requirements: Sample type – 24h urine collection in a plain collection bottle
Turnaround time: 2 weeks
Additional information:
Referred test: Referred test
Location: UCLH