From the Guidelines
A metabolic stone workup is not recommended after the first kidney stone episode for most low-risk patients, but it should be considered in high-risk individuals, such as those with a family history of stones, early onset stone disease, or stones composed of uric acid, cystine, or struvite. The American Urological Association guideline 1 suggests that clinicians should perform additional metabolic testing in high-risk or interested first-time stone formers and recurrent stone formers. According to the guideline, urinary saturation of stone-forming salts has been shown to correlate with stone composition, suggesting that 24-hour urine testing can be used to inform and monitor treatment protocols.
For low-risk patients with a first-time uncomplicated stone, initial management should focus on increased fluid intake (aiming for 2-2.5 liters of urine output daily) and dietary modifications, as recommended by the American College of Physicians guideline 1. This includes moderate sodium restriction (2,300 mg/day), normal calcium intake (1,000-1,200 mg/day), and limiting animal protein and oxalate-rich foods.
However, for high-risk patients, a comprehensive metabolic evaluation should be performed after the first stone episode. This evaluation should include stone analysis, serum intact parathyroid hormone level, and 24-hour urine collections to identify metabolic and environmental risk factors that can help direct dietary and medical therapy. The rationale for this selective approach is that many first-time stone formers will not develop recurrent stones, making extensive testing cost-ineffective for all patients. However, early identification of metabolic abnormalities in high-risk individuals can lead to targeted interventions that significantly reduce recurrence rates and prevent kidney damage.
Key considerations for a metabolic stone workup include:
- Stone composition, as certain types (e.g., uric acid, cystine, or struvite) may indicate underlying metabolic or genetic abnormalities
- Family history of stones
- Early onset stone disease (before age 25)
- Solitary kidney
- Chronic kidney disease
- Recurrent urinary tract infections
- 24-hour urine testing to inform and monitor treatment protocols
- Dietary modifications, such as increased fluid intake and moderate sodium restriction, to prevent recurrent stones.
From the Research
Metabolic Stone Workup After First Stone Episode
- A metabolic stone workup is recommended for all stone formers to prevent recurrent disease 2.
- The workup should include a medical and lifestyle history, physical examination, basic urine and blood analysis, radiological examination, and stone analysis 2.
- A 24-h urine analysis should be performed to understand the lithogenic process and guide follow-up 2.
- However, one study suggests that a 24-h urine metabolic profile may be postponed until a recurrent stone event in first-time stone formers without comorbidities 3.
Importance of 24-Hour Urine Collection
- A 24-hour urine collection is an integral part of nephrolithiasis workup and can help identify lithogenic risk factors 4.
- The collection can provide information on urine volume, urinary levels of sodium, calcium, uric acid, oxalate, and citrate 3.
- However, one study found that a single 24-hour urine collection may not be adequate, and two collections may be necessary to optimize diagnostic yield 5.
Individualized Metabolic Workup
- The metabolic workup should be individualized according to stone type and severity of the disease 6.
- The workup should include analysis of stone composition, blood, and urine, as well as a careful medical history and imaging 6.
- The treatment should be tailored to the individual patient, taking into account their medical history, dietary and drinking habits, lifestyle, and ongoing pharmacological therapy 6.