In patients at high risk for developing another stone, a metabolic evaluation is usually recommended. This includes analysis of the stone, blood tests, and a 24-hour urine collection. The urine collection involves saving urine for 24 hour period and taking the collection or sending a small sample of the collection to a laboratory. Tests will be performed to determine if there are any abnormalities in a stone patient’s metabolism that puts them at higher risk for forming more stones. The results of these tests will then be discussed with a patient to choose a treatment plan individualized to their unique situation.
Specific medical conditions that predispose to stones
In a minority of stone patients, an identifiable medical condition can be the cause of stones. These uncommon conditions include primary hyperparathyroidism, renal tubular acidosis, cystinuria, hyperoxaluria, and gouty diathesis. In these situations, specific treatments can help prevent or reduce future stone development.
Other abnormalities in metabolism that predispose to stones
In the majority of stone patients, more subtle abnormalities may be present that increase their risk for developing stones. Identifying these abnormalities can help direct specific dietary or pharmaceutical treatments to lower the chances of another stone from forming. These abnormalities can occur together and include:
- Low urine volume
- Hypercalciuria (high calcium concentrations in urine)
- Hyperoxalauria (high oxalate concentrations in urine)
- Hypocitraturia (low citrate levels in urine)
- Hyperuricosuria (high uric acid levels in urine)
Additionally, there are other factors that can put someone at increased risk for forming stones including gender, race, age, geography, climate, body weight, occupation, the presence of urinary infections, and anatomic abnormalities.