Definition
Urolithiasis is the formation of stones anywhere in the urinary tract (the kidney, ureter, or bladder). Renal or ureteric colic generally describes an acute and severe loin pain caused when a urinary stone moves from the kidney or obstructs the flow of urine through the ureter.
Pathophysiology
Urinary stones form when the urine becomes excessively supersaturated with a mineral, leading to crystal formation. Once crystals are formed, they either pass out with the urine or are retained in the kidney, where they can grow and form stones.
Urinary stones are often asymptomatic but may cause pain when they move or obstruct the flow of urine through the ureter. Obstruction of urinary flow causes an increase in tension in the urinary tract wall. The increasing pressure stimulates the synthesis and release of prostaglandins, and subsequent vasodilatation induces a diuresis which further increases pressure within the kidney.
Pain from urinary stones can also be due to smooth muscle spasm (as a result of prostaglandins acting directly on the ureter), hyperperistalsis (due to the obstruction), oedema, and mucosal irritation.
Common Obstruction Sites
Vesico-ureteric Junction
Where ureter enters the bladder - most common site of obstruction
Mid-ureter
Where ureter crosses the iliac vessels
Pelvi-ureteric Junction
Where renal pelvis meets ureter
Types of Stones
Calcium stones (80%)
- Calcium oxalate stones (80% of calcium stones)
- Calcium phosphate stones (20% of calcium stones)
- Associated with low urine volume, hypercalciuria, hyperuricosuria, hyperoxaluria, and hypocitraturia
Uric acid stones (10-20%)
- Associated with hyperuricosuria
- Low urinary pH (less than 5.5)
Struvite stones (1-5%)
- Infection stones from bacterial urea hydrolysis
- High urine pH (greater than 7.2)
- Mixture of magnesium, ammonium, and phosphate
Cystine stones (1%)
- Result from genetic cystinuria
- Cystine leaks through kidneys into urine
Drug-induced stones (1%)
- Formed by crystallised drugs or urine composition changes
- Includes acetazolamide, allopurinol, vitamin D, topiramate, etc.
Risk Factors
Demographic
- Age: Peak incidence 40-60 years (low in children/elderly)
- Gender: 3:1 male to female ratio
- Ethnicity: Most common in white people
Lifestyle
- Diet high in oxalate, urate, sodium, animal protein
- Chronic dehydration
- Obesity
- High ambient temperatures
Medical
- Family history
- Anatomical urinary tract abnormalities
- Gastrointestinal conditions
- Genetic conditions
- Conditions altering urine volume/pH
Clinical Features
Renal or ureteric colic is characterized by:
- Abrupt onset of severe unilateral abdominal pain
- Originates in loin/flank, radiates to groin/genitals
- Pain lasts minutes to hours in spasms
- Often described as most severe pain experienced
- Accompanied by nausea, vomiting, haematuria
- May have dysuria, frequency, straining
- Patient restless, unable to lie still
Investigations
Urine Dipstick
- Check for haematuria (supports but doesn't confirm diagnosis)
- Check for nitrite/leucocyte esterase (suggests UTI)
Imaging
| Patient Group |
Recommended Imaging |
Timing |
| Most adults |
Low-dose non-contrast CT KUB |
Within 24 hours |
| Pregnant women |
Ultrasound |
Avoid CT |
| Children/young people |
Ultrasound first, then CT if uncertain |
As clinically indicated |
Management
Immediate Hospital Admission Required If:
- Systemic infection/sepsis
- Increased risk of acute kidney injury
- Chronic/transplanted kidney disease
- Bilateral stones suspected
- Unable to take oral intake
- Diagnosis doubtful
Pain Relief
First Line
NSAID by any route (PR, oral, IV)
Preferred due to prostaglandin inhibition
Second Line
IV Paracetamol if NSAID contraindicated or ineffective
Third Line
Opioid analgesic if both NSAIDs and IV paracetamol contraindicated/ineffective
Do not offer antispasmodics for renal/ureteric colic
Treatment Options by Stone Size
<5mm Stones
- Watchful waiting with analgesia
- High fluid intake (2-3L/day)
- 90% pass spontaneously
- Follow-up in 4-6 weeks
5-10mm Stones
- Medical expulsive therapy
- Alpha-blockers (tamsulosin)
- 50-80% pass spontaneously
- Surgical intervention if fails
>10mm Stones
- Surgical intervention required
- Shockwave lithotripsy (SWL)
- Ureteroscopy (URS)
- Percutaneous nephrolithotomy (PCNL)
Surgical Treatment Options
Shockwave Lithotripsy (SWL)
Non-invasive outpatient treatment using shock waves to fragment stones
- Best for: Renal stones <2cm, upper ureteric stones
- Success rate: 70-90%
- Advantages: Non-invasive, outpatient procedure
Ureteroscopy (URS)
Endoscopic procedure with laser stone fragmentation
- Best for: Lower ureteric stones, failed SWL
- Success rate: 85-95%
- Advantages: High success rate, stone retrieval possible
Percutaneous Nephrolithotomy (PCNL)
Surgical procedure through small back incision for large stones
- Best for: Large renal stones >2cm, complex stones
- Success rate: 90-95%
- Advantages: Best for large stones, complete clearance
Metabolic Testing & Prevention
Metabolic Workup
- Stone analysis for all first-time stone formers
- Measure serum calcium and parathyroid hormone
- 24-hour urine collection for recurrent stone formers
- Refer children to pediatric nephrologist/urologist
Prevention Advice
- Fluid intake: 2-3L daily to produce 2L urine
- Citrate: Add fresh lemon juice to water
- Avoid: Carbonated drinks, high oxalate foods
- Salt: Reduce to <6g daily
- Calcium: Don't restrict dietary calcium
- Protein: Moderate animal protein intake
- Weight: Maintain healthy BMI
Complications
Main Complications
- Obstruction: Can decrease GFR, cause irreversible kidney damage if persisting >48 hours
- Infection: Obstructive pyelonephritis or pyonephrosis (life-threatening sepsis risk)
Other Complications
- Renal carcinoma
- Chronic kidney disease (CKD)
- Coronary heart disease (CHD)
- Rare rupture with urinoma formation
- Ureteral stricture
- Recurrent stone formation