Nephrolithiasis: Workup and Management
Initial Diagnostic Approach
For suspected nephrolithiasis, obtain low-dose non-contrast CT as the first-line imaging modality, which has become the gold standard for detecting ureteral calculi. 1
Essential Initial Workup
- Imaging: Low-dose CT without contrast is the diagnostic method of choice for acute presentations, providing rapid and accurate stone detection 1
- Urinalysis: Check for hematuria, though its absence does NOT exclude nephrolithiasis—up to 20-80% of cases may lack hematuria 2
- Stone analysis: Obtain stone composition analysis for ALL first-time stone formers, as approximately 80% are calcium-based (oxalate/phosphate), with uric acid and struvite being less common 3
- Metabolic evaluation: Perform 24-hour urine collection measuring volume, pH, calcium, oxalate, uric acid, citrate, sodium, potassium, and creatinine 4, 5
Critical pitfall: Absence of hydronephrosis on ultrasound never excludes kidney stones, and conversely, pelvic dilation does not necessarily indicate obstruction 2
Acute Management of Renal Colic
NSAIDs (diclofenac, ibuprofen, or metamizole) are first-line therapy for renal colic pain, as they reduce the need for additional analgesia compared to opioids. 4
Pain Management Algorithm
- First-line: NSAIDs at the lowest effective dose (cardiovascular and GI risks must be considered) 4
- Second-line: Opioids (hydromorphine, pentazocine, or tramadol—NOT pethidine) only when NSAIDs are contraindicated or insufficient 4
- Medical expulsive therapy: Alpha-blockers are strongly recommended for distal ureteral stones >5 mm in patients suitable for conservative management 4
Emergency Indications Requiring Urgent Intervention
Immediate decompression via percutaneous nephrostomy or ureteral stenting is mandatory for:
- Sepsis with obstructed kidney 4
- Anuria in an obstructed kidney 4
- Administer antibiotics immediately and adjust based on culture results in infected cases 4, 6
Conservative vs. Surgical Management Decision
Stone Size Criteria
- ≤5 mm: Conservative management with hydration and medical expulsive therapy is appropriate 2
- 6-20 mm: Stones <6 mm can pass spontaneously; consider shock wave lithotripsy (SWL) or ureteroscopy (URS) if symptomatic and failing conservative management 7, 1
- >20 mm: Percutaneous nephrolithotomy (PCNL) should be offered as first-line surgical therapy 7
Asymptomatic calyceal stones may be observed via active surveillance, particularly lower pole stones. 1
Medical Prevention of Recurrence
First-Line: Fluid Management
Increase fluid intake to achieve at least 2 liters (preferably 2-2.5 liters) of urine output daily, which reduces stone recurrence by approximately 50%. 3, 4, 7
- Water is preferred, though coffee, tea, beer, and wine also reduce stone risk 7
- Avoid: Grapefruit juice (increases stone risk by 40%) and colas acidified with phosphoric acid 3, 7
- Tap water and mineral water show no significant difference in efficacy 3
Pharmacologic Monotherapy (When Fluids Fail)
For patients with active recurrent disease where increased fluid intake fails, use pharmacologic monotherapy with thiazide diuretics, citrate, or allopurinol. 3
Drug Selection and Dosing
Thiazide diuretics (for hypercalciuria >200 mg/day):
- Hydrochlorothiazide 50 mg daily 3, 4
- Chlorthalidone 25-50 mg daily 3, 4
- Indapamide 2.5 mg daily 3, 4
- Note: Higher doses are more effective but carry more adverse effects; lower doses have unknown efficacy 3
Potassium citrate (for hypocitraturia <320 mg/day):
- 30-100 mEq/day, targeting urinary pH 6.0-6.5 4, 7
- Critical: Use potassium citrate, NOT sodium bicarbonate or sodium citrate, as sodium load increases calcium excretion 5
Allopurinol (for hyperuricosuria):
Combination therapy is NOT more beneficial than monotherapy and should be avoided to minimize adverse effects. 3, 4
Dietary Modifications
Evidence-Based Dietary Recommendations
- Maintain normal dietary calcium: 1,000-1,200 mg/day from food sources, NOT supplements 4, 5, 7
- Limit sodium: ≤2,300 mg/day to reduce urinary calcium excretion 4, 5, 7
- Reduce animal protein: 5-7 servings of meat, fish, or poultry per week 5, 7
- Limit oxalate intake: For patients with calcium oxalate stones 5
- Increase fruits and vegetables: Counterbalances acid load and raises urinary pH 7
- Avoid excessive vitamin C supplementation: Can increase oxalate excretion 5
Stone-Specific Management
Uric Acid Stones
Potassium citrate is first-line therapy to raise urine pH to 6.0, as most patients have low urinary pH rather than hyperuricosuria as the predominant risk factor. 4
- Oral chemolysis with alkalinization (citrate or sodium bicarbonate to pH 7.0-7.2) can dissolve existing uric acid stones 4
Cystine Stones
Use a stepwise approach:
- Increased fluid intake 4
- Sodium and protein restriction 4
- Urinary alkalinization with potassium citrate to achieve urine pH of 7.0 4
Monitoring and Follow-Up
Metabolic Monitoring Protocol
- 6 months post-treatment: Obtain 24-hour urine collection to verify urine volume >2 L/day and assess metabolic parameters 4, 7
- Annual monitoring: Continue yearly 24-hour urine collections to assess adherence and metabolic response 4
- Urinary pH: Ensure pH remains 6.0-6.5 and does not exceed 7.0 7
Adverse Effect Monitoring
Obtain periodic blood testing for patients on pharmacologic therapy to monitor for: 4
- Hypokalemia and glucose intolerance (thiazides)
- Elevated liver enzymes (allopurinol, tiopronin)
- Anemia (acetohydroxamic acid, tiopronin)
- Hyperkalemia (potassium citrate)
Stone Analysis Follow-Up
Obtain repeat stone analysis in patients not responding to treatment, as stone composition may change over time. 4
Key Clinical Caveats
- Do NOT increase fluids in patients already drinking recommended amounts or those with contraindications to increased fluid intake 3, 7
- Avoid excessive hydration in acute obstruction—an obstructed kidney protects itself 2
- Evidence is insufficient to guide treatment based solely on stone composition or biochemistry without metabolic evaluation 3, 4
- Most trial evidence applies only to calcium stone formers; no trials have assessed treatment for uric acid or cystine stones specifically 3