Renal stones as also referred to as renal calculi, urolithiasis and nephrolithiasis. They are hard stones that form in the renal pelvis, where the urine collects before travelling down the ureters. They may be asymptomatic until they irritate or get stuck in the ureters. They might get stuck at any point along the ureters, but commonly at the vesico-ureteric junction.
Two key complications are:
- Obstruction leading to acute kidney injury
- Infection with obstructive pyelonephritis
Types
Calcium-based stones are the most common type of kidney stone (about 80%). Having a raised serum calcium (hypercalcaemia) and a low urine output are key risk factors for calcium collecting into a stone. There are two types of calcium stones:
- Calcium oxalate (more common)
- Calcium phosphate
Other types of kidney stones include:
- Uric acid – these are not visible on x-ray
- Struvite – produced by bacteria, therefore, associated with infection
- Cystine – associated with cystinuria, an autosomal recessive disease
Staghorn Calculus
A staghorn calculus is where the 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. They may be seen on plain x-ray films.
Most commonly, this occurs with stones made of struvite. In recurrent upper urinary tract infections, the bacteria can hydrolyse the urea in urine to ammonia, creating the solid struvite.
Presentation
Renal stones may be asymptomatic and never cause an issue.
Renal colic is the presenting complaint in symptomatic kidney stones. Renal colic is:
- Unilateral loin to groin pain that can be excruciating (“worse than childbirth”)
- Colicky (fluctuating in severity) as the stone moves and settles
Patients often move restlessly due to the pain.
There may also be:
- Haematuria
- Nausea or vomiting
- Reduced urine output
- Symptoms of sepsis, if infection is present
Investigations
Urine dipstick usually shows haematuria in cases of kidney stones. A normal urine dipstick does not exclude stones. Urine dipsticks are also helpful to exclude infection.
Blood tests help establish signs of infection and also kidney function. Checking the serum calcium helps identify hypercalcaemia that may have caused the kidney stone.
An abdominal x-ray can show calcium-based stones, but uric acid stones will not show up (they are radiolucent).
Non-contrast computer tomography (CT) of the kidneys, ureters and bladder (CT KUB) is the initial investigation of choice for diagnosing kidney stones. The NICE guidelines (2019) recommend a CT within 24 hours of the presentation.
Ultrasound of the kidneys, ureters and bladder (ultrasound KUB) is a less preferred alternative to CT scan. A negative result does not exclude kidney stones. It is less effective at identifying kidney stones but is helpful in pregnant women and children.
Stones can be analysed to determine the type, which can help establish the cause and reduce the risk of recurrence.
TOM TIP: Remember hypercalcaemia as a cause of kidney stones. You can remember the presentation of hypercalcaemia with the mnemonic “renal stones, painful bones, abdominal groans and psychiatric moans”. The three causes to remember are calcium supplementation, hyperparathyroidism and cancer (e.g., myeloma, breast or lung cancer).
Management
NSAIDs are the most effective type of analgesia, for example, intramuscular diclofenac. IV paracetamol is an alternative, where NSAIDs are not suitable. Opiates are not very helpful for pain management and are not routinely used.
Antiemetics are used for nausea and vomiting (e.g., metoclopramide, prochlorperazine or cyclizine).
Antibiotics are required if infection is present.
Watchful waiting is usually used in stones less than 5mm, as there is a 50-80% chance they will pass without any interventions. It may also be suitable for patients with stones 5-10mm, depending on individual factors. It can take several weeks for the stone to pass.
Tamsulosin (an alpha-blocker) can be used to help aid the spontaneous passage of stones.
Surgical interventions are required in large stones (10mm or larger), stones that do not pass spontaneously or where there is complete obstruction or infection.
Surgical Interventions
Extracorporeal shock wave lithotripsy (ESWL):
ESWL involves an external machine that generates shock waves and directs them at the stone under x-ray guidance. The shockwaves break the stone into smaller parts to make them easier to pass.
Ureteroscopy and laser lithotripsy:
A camera is inserted via the urethra, bladder and ureter, and the stone is identified. It is then broken up using targeted lasers, making the smaller parts easier to pass.
Percutaneous nephrolithotomy (PCNL):
PCNL is performed in theatres under a general anaesthetic. A nephroscope (small camera on a stick) is inserted via a small incision at the patient’s back. The scope is inserted through the kidney to assess the ureter. Stones can be broken into smaller pieces and removed. A nephrostomy tube may be left in place after the procedure to help drain the kidney.
Open surgery:
Open surgery can be used to access the kidneys and remove the stones. This is rarely needed as other, less invasive, methods are usually effective.
Recurrent Stones
One episode of renal stones predisposes patients to further episodes. NICE guidelines (2019) recommend advising patients to:
- 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 (cola drinks contain phosphoric acid, which promotes calcium oxalate formation)
- Reduce dietary salt intake (less than 6g per day)
- Maintain a normal calcium intake (low dietary calcium might increase the risk of kidney stones)
Other common recommendations include:
- For calcium stones – reduce the intake of oxalate-rich foods (e.g., spinach, beetroot, nuts, rhubarb and black tea)
- For uric acid stones – reduce the intake of purine-rich foods (e.g., kidney, liver, anchovies, sardines and spinach)
- Limit dietary protein
Two medications that may be used to reduce the risk of recurrence are:
- 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
Last updated May 2021