Kidney Stones

What are kidney stones?

Kidney stones form within the urine collecting system of the kidney (calyces and renal pelvis).  If they pass into the ureter (tube connecting the kidney to the bladder) then can block the outflow of the kidney and cause a back of urine (hydronephrosis). This obstruction and pressure usually cause pain. The stones may pass from the ureter into the bladder where they are usually passed in the urine.

Kidney stones are very common and the lifetime risk of developing a kidney stone is up to 10%. Men are more commonly affected than women.

There are several kinds of kidney stones:

  • Calcium oxalate – are formed from calcium combined with oxalate. These are the most common type
  • Uric acid – are developed from crystals of uric acid in highly acidic urine
  • Struvite – struvite is a hard-crystalline form of magnesium ammonium phosphate. Kidney stones of this substance are formed in patients with urine infections caused by certain types of bacteria. These often form “Staghorn calculi” (large branched stones)
  • Cystine – cystine is an amino acid found in proteins and may form stones when it is excreted in excessive amounts in the urine, due to a hereditary cause

What causes kidney stones to form?

Kidney stones usually form in concentrated urine (darker colour) because there is an excess of certain chemical elements/minerals in the urine compared to the volume of urine. The urine becomes supersaturated (overloaded) with these compounds that can form stones, and they bind together to create solid crystals, which grow into stones.

Thus, the most common cause is dehydration.

Other conditions which can predispose to formation of kidney stones include:

  • Excess consumption of oxalate containing foods, salts and animal proteins
  • Gout
  • Inflammatory bowel disease
  • Renal Tubular Acidosis
  • Sarcoidosis
  • Hyperparathyroidism
  • Medullary sponge kidney
  • Adult Polycystic Kidney disease
  • Cystinuria – genetic condition resulting in high levels of cysteine in urine
  • Medications: high doses of Vitamin C & D, some HIV medications
  • Urinary tract infections
  • Anatomical abnormalities within the urinary tract

What are the symptoms of kidney stones?

  • Asymptomatic – if they are in the kidney and/or not causing obstruction
  • Pain – usually in the flank and the groin (“loin to groin”); often described as one of the worst pains people experience
  • Haematuria – blood in urine
  • Urinary tract infections – fever, burning with urination
  • Nausea & vomiting

How are kidney stones diagnosed?

  • A CT scan of the kidneys and ureters (CT KUB) is the best test to detect stones.
  • Provides details on the number of stones, their size and location
  • Stones may also be detected on an ultrasound of the kidneys or a plain X-ray, however these are less sensitive than a CT and can easily miss stones
  • You will also need to have a urine and blood test to check for infection and kidney function

How are kidney stones treated?

This depends on:

  • Number of stones
  • Size of stone(s)
  • Location of stone(s)
  • If infection is present
  • Type/composition of stone (if known)
  • Patient preference

How are stones in the kidney treated?

  • 1. Observation: for small (usually <3-4mm) asymptomatic stones
  • Regular x-rays or ultrasound to ensure the stones are not growing
  • 2. ESWL – Extra corporeal shock wave lithotripsy
  • Using shock/sound waves to target the stone resulting in fragmentation. The small fragments are then passed
  • This procedure is minimally invasive and usually performed under sedation
  • ESWL is less effective for large stones (>2cm), very hard stones (cysteine) or stones located in the lower part of the kidney
  • Direct visualisation and destruction of stone with a high-power laser through a small telescope passed into the kidney from below
  • The tiny fragments then pass or are extracted with a small basket
  • A ureteric stent is usually left for 1-2 weeks after the procedure
  • Although more invasive than ESWL, this technique is more effective at treating larger and multiple stones than ESWL, irrespective of their location
  • 4. PCNL – Percutaneous Nephrolithotomy
  • For large stones within the kidney (>2cm)
  • The kidney is accessed via a keyhole through the back and the stone is visualised with a telescope and destroyed with a Lithoclast master device (a type of small “jack hammer”)
  • 5. Open/laparoscopic (key hole) procedures:
  • Seldom performed these days but may be occasionally required for complex cases
  • If the affected kidney is poorly functioning, sometimes it is completely removed (nephrectomy), which is usually performed laparoscopically
  • 6. Dissolution therapy
  • Dissolving the stone
  • Only possible for some types of stones (uric acid stones)
  • You will be required to a strict course of medications which make the urine more alkaline (less acidic) will need to be taken strictly (eg. Ural) as well as reduce the levels of uric acid in the blood (Allopurinol)
  • You will also need to significantly increase you intake of water (2-3L a day) unless this is contraindicated because of certain heart conditions
  • Dissolution is slow and only suitable for stones which are not causing symptoms

How are stones in the ureter treated?

These usually produce severe pain (renal colic) and more urgent treatment may be required.

The best pain regimen for this type of pain includes (in order of preference):

  • Paracetamol
  • Anti-inflammatories e.g. Neurofen, Indocid, Voltaren (if no contraindications)
  • Endone
  • Morphine
  • 1. Medical expulsive therapy (MET): expectant management of waiting for the stone to pass is usually only possible if:
  • Pain is under control with tablets
  • No fever or other signs of infection
  • Kidney function is normal
  • The stone is <6mm in size (ie. good chance to pass spontaneously)
  • Medical expulsion therapy involves:
  • Taking Tamsulosin (Flomaxtra) a medication which increases the chance of stone passage
  • A follow up x-ray/CT to ensure the stone has passed (not needed if urine is strained and the stone is caught)
  • Note - it is critically important to know that the stone has passed one way or another because a retained stone can result in “silent” (asymptomatic) loss of an entire kidney if left untreated
  • There are signs of infection
  • Pain, nausea or vomiting are persisting
  • The stone stone is large (≥6mm) and unlikely to pass spontaneously
  • Note – the stent does not remove the stone; it bypasses it and allows urine to drain past the stone, thus relieving the obstruction. The stent will also allow the ureter to expand, which makes subsequent procedures to treat the stone easier. A ureteric stent is not permanent and always needs to be removed or changed.
  • Direct visualisation and destruction of stone with a high-power laser through a small telescope passed into the ureter from below
  • The tiny fragments then pass or are extracted with a small basket
  • A ureteric stent is usually left for 1-2 weeks after the procedure

How can I prevent kidney stones in the future?

  • General lifestyle modifications include:
  • Increasing fluid intake
  • Reducing salt intake
  • Reducing animal protein intake (meat, fish, chicken)
  • Reducing intake of high oxalate containing foods (nuts, beetroot, rhubarb, strawberries, potatoes, chocolate)
  • Sometimes further evaluation and specialised treatment is required for some metabolic abnormalities, which predispose to stones. This may involve:
  • Analysis of the stone type
  • Blood tests – check for calcium, parathyroid and uric acid levels
  • 24 hours urine collection test
  • Referral to a renal physician or endocrinologist
  • Note – despite all preventative measures there is a 50% chance of forming more stones within 10 years of having them treated.