Urology - kidney stones Flashcards
Two key complications of kidney stones
Obstruction - leading to AKI
Infection - obstructive pyelonephritis
Types of kidney stones
Calcium based are the most common by far:
- Calcium oxalate (most common)
- Calcium phosphate
Other types:
- Uric acid (not visible on X-ray)
- Struvite – produced by bacteria, therefore, associated with infection
- Cystine – associated with cystinuria, an autosomal recessive disease
Risk factors for kidney stones
Raised serum calcium
Low urine output
Differential diagnosis for flank pain
Renal colic Pyelonephritis Ruptured AAA Biliary pathology Bowel obstruction Lower lobe pneumonia MSK pain
What is a staghorn calculus?
Stone forms in the shape of the renal pelvis, giving it a similar appearance to the antlers of a deer stag.
(The body sits in the renal pelvis with horns extending into the renal calyces.)
Most commonly occurs with struvite stones
Presentation of renal stones
May be asymptomatic
Renal colic:
- Severe unilateral loin to groin pain
- Colicky
Haematuria
Nausea and vomiting
Reduced urine output
Symptoms of sepsis if infection present
Investigations in renal stones/colic
Urine dip - may show haematuria, useful to exclude infection
Bloods - FBC/CRP (infection), U&Es
Non contrast CT is the gold standard
Management of renal colic
Analgesia - NSAIDs more effective than paracetamol
Antiemetics if needed
Antibiotics if infection
Watchful waiting for stones to pass (if less than 5mm) - will often pass spontaneously
Surgical interventions for stones which are >10mm or which aren’t passing spontaneously
Surgical intervention options for renal stones
Extracorporeal shock wave lithotripsy
Ureteroscopy and laser lithotripsy
Percutaneous nephrolithotomy (PCNL) under GA - nephroscope passed through incision in back and stones removed
Open surgery is an option but rarely needed
Prevention of recurrent stones
Increase oral fluid intake (2.5 – 3 litres per day)
Add fresh lemon juice to water (citric acid binds to urinary calcium reducing the formation of stones)
Avoid carbonated drinks ( contain phosphoric acid, which promotes calcium oxalate formation)
Reduce dietary salt intake < 6g per day
Maintain a normal calcium intake (low dietary calcium might increase the risk of kidney stones)
For calcium stones - can also reduce intake of oxalate rich foods e.g. spinach, nuts and beetroot
For uric acid stones - educe the intake of purine-rich foods (e.g., kidney, liver)
Medications that may be used to reduce risk of recurrence of renal stones
Potassium citrate in patients with calcium oxalate stones and raised urinary calcium
Thiazide diuretics (e.g., indapamide) in patients with calcium oxalate stones and raised urinary calcium
