Renal Calculus (Kidney Stones)

Urinary stones affect 1 in 10 Australians. Most pass spontaneously, but ongoing pain, renal impairment or infection mandate intervention. The two main stone types are calcium and uric acid.

Presentation

• Acute-onset severe unilateral flank/lower abdominal pain — sharp, stabbing, cramping
• Lower urinary tract symptoms (haematuria, dysuria, frequency) can indicate distal stone migration
• Nausea, sometimes vomiting
• Fevers are important to elicit — an infected stone must be removed

Examination

Abdomen often soft and non-tender; flank tenderness and a positive renal angle punch test on the affected side. Urine dip may show blood, leukocytes and protein — nitrites plus fever raise suspicion of an infected stone.

Investigations

• Non-contrast CT KUB is first-line imaging in older patients (an ultra-low-dose protocol is acceptable for anyone over 18 — radiation dose is roughly equivalent to 10 abdominal X-rays)
• USS KUB can show hydronephrosis and possible stone shadowing; if significant hydronephrosis or renal impairment is present, urologists will still want a CT KUB to plan their approach
• FBC, renal function, inflammatory markers
• X-ray KUB can confirm a radio-opaque stone for monitoring passage

Pain management — mechanism and hierarchy

Renal tract pain is mediated by a prostaglandin surge causing arteriolar vasodilatation, increased vascular permeability, and ureteric oedema/spasm — the progressive stone passage along the ureter causes the classic referred/migratory pain pattern.

• Paracetamol and NSAIDs are both effective and superior to opioids for analgesic efficacy, with less need for rescue analgesia. NSAIDs reduce prostaglandin production, lowering GFR by up to 35% and thus reducing renal pelvic pressure and stretch-receptor stimulation; they also directly relax ureteric smooth muscle. Available orally, IV, or per rectum (rectal administration may give better local anti-inflammatory control).
• Caution: NSAIDs can worsen acute renal failure in patients with underlying CKD — use the lowest effective dose for the shortest time.
• Opioids are second-line — for NSAID contraindication or inadequate control. Provide only short-term relief, need repeat dosing, and carry a less favourable side-effect profile (nausea, sedation, respiratory depression, constipation) with prolonged use. Combining opioids with paracetamol/NSAIDs gives synergistic pain control with an opioid-sparing effect.

Conservative management

If no obstructive uropathy and the stone is ≤6mm at its largest diameter: conservative management with NSAID suppository analgesia, good oral hydration, and asking the patient to try to catch/strain the stone for analysis. ~70% of these stones pass spontaneously.

Medical expulsive therapy (MET) with alpha-blockers — evidence has narrowed since earlier practice. A meta-analysis of alpha-blockers as a class found increased stone expulsion (RR 1.54), reduced time to expulsion, and reduced analgesia use. Tamsulosin is the most studied agent and proved most efficacious specifically for larger stones (>5mm) in the distal ureter — current EAU/AUA guidance treats MET as a selective adjunct for this group rather than a routine addition for all sub-6mm stones (most of which pass regardless). Tamsulosin is not PBS-subsidised for this indication; the most common side effect is transient postural hypotension (~4.2%). Newer, more selective agents in the same class include silodosin and naftopidil. Alpha-blockers are also studied post-lithotripsy to aid passage of residual fragments.

Repeat imaging 6 weeks after a stone passes to confirm resolution in patients with asymptomatic obstruction.

When surgery is needed

Obstructive uropathy or a concurrent UTI mandate surgical intervention — untreated infection with obstruction risks calyceal rupture and pyelovenous/pyelolymphatic spread, causing severe sepsis.

Relative surgical indications:

• Stone >6mm
• Ongoing/recurrent pain
• Occupational/social circumstances (e.g. airline pilots, an important upcoming event or planned remote travel)

Surgical options for obstructing stones:

• Ureteroscopic laser lithotripsy — the most-used option over the last 15 years, more widely available in the last 10; often combined with ureteric stenting (painful, minimum 2 weeks in situ before removal)

Treatment of stones still in the kidney (to prevent future obstruction):

• Shockwave lithotripsy — stones <1cm
• Retrograde uretero-pyeloscopic laser lithotripsy — stones 1–2cm
• Percutaneous nephrolithotomy — stones >2cm
• Open nephro/pyelolithotomy — rare, for staghorn calculi; ~6 week recovery

Prevention

Recurrence rate is high — 50% within 5 years. Lifestyle/dietary measures have controversial evidence but are reasonable to offer: increased fluid intake, avoid added salt, balanced diet. Stone-type-specific prevention:

• Calcium stones — reduce salt, avoid an oxalate-rich diet (tea, chocolate, spinach, beetroot, rhubarb, peanuts, cola, vitamin C)
• Uric acid stones — treat as for gout prophylaxis

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Sources: https://www.racgp.org.au/download/documents/AFP/2011/October/201110macneil.pdf, EAU Guidelines on Urolithiasis (https://uroweb.org/guidelines/urolithiasis)