Renal Stones (Nephrolithiasis)

Renal calculi are formed when the urine is supersaturated with salt and minerals such as calcium oxalate, struvite, uric acid and cystine.¹ They vary considerably in size from small " gravel like" stones, to large " staghorn" calculi. The calculi may stay in the position in which they are formed, or migrate down the urinary tract producing symptoms along the way. Recent studies suggest that the initial factor involved in the formation of a stone may be the presence of nanobacteria that form a calcium phosphate shell. These small intracellular bacteria are present at the centre of over 95% of all stones.²

• Renal stones are common, being present at some time in one in ten of the population, although a significant proportion will remain asymptomatic.
• Men are more commonly affected than women with a male to female ratio of 3:1.
• The peak age for developing stones is between 30 and 50, and recurrence is common.

Risk factors

Several risk factors are recognised to increase the potential of a susceptible individual to develop stones, these include:

• Anatomical anomalies in the kidneys and/or urinary tract e.g. horseshoe kidney, ureteral stricture
• Family history of renal stones
• Hypertension
• Gout
• Hyperparathyroidism
• Immobilisation
• Relative dehydration
• Metabolic disorders which increase excretion of solutes e.g. chronic metabolic acidosis, hypercalciuria , hyperuricosuria
• More common in hot climates

• Many stones are asymptomatic and discovered during investigations for other conditions.
• Other stones may be diagnosed by a classical presentation of colicky abdominal pain radiating from the loin to the groin. Other symptoms which may be present include:
  • Rigors and fever
  • Dysuria
  • Haematuria
  • Urinary retention
  • Nausea and vomiting
• Examination: localised abdominal tenderness; possibly palpable bladder and/or kidney(s).

Other diagnoses which must be considered in the acute situation are other causes of colicky abdominal pain e.g. bowel obstruction, strangulated hernia, pain due to bowel muscle spasm, appendicitis ,other forms of renal colic such as "clot" colic secondary to trauma and bleeding of the kidney, and other causes of urinary retention such as prostatism.

• Urine culture and microscopy looking for infection
• Urine dip testing for blood and pH
• Renal function and electrolytes: looking for evidence of renal impairment
• Serum calcium, urate , phosphate and bicarbonate
• Parathyroid hormone level
• X-ray and renal ultrasound: presence and position of stones
• Helical CT scan to confirm diagnosis and more accurately assess the size and position of stone

Initial management can either be done as an inpatient or an urgent outpatient basis, usually depending on how easily the pain can be controlled.³

• Indications for hospital admission:
  • Fever
  • Solitary Kidney
  • Known non functioning kidney
  • Inadequate pain relief or persistent pain
  • Poor social support
  • Inability to arrange urgent OPD follow-up
• Indication for urgent out-patient appointment:
  • Pain has been relieved
  • Patient able to drink large volumes of fluid
  • Adequate social circumstances
  • No complications evident

Initial management of acute presentation

• The pain of renal colic is very severe, and the immediate requirement will be for symptomatic relief. Immediate pain control may be achieved either with pethidine or diclofenac by injection, or diclofenac by suppository in addition to local heat pads.
• A calcium channel blocker such as nifedipine may help to relax the ureteral muscles and aid passage of the stone.
• Additional treatment with regular analgesia, antibiotics and a short course of prednisolone to reduce the inflammation secondary to the stone have all been found to be of value in assisting the spontaneous passage of the stone.⁴
• The majority of stones will pass spontaneously but may take 1-3 weeks, patients who have not passed a stone or who have continuing symptoms should have the progress of the stone monitored at at least weekly intervals to assess the progression of the stone.
• Conservative management may be continued for up to three weeks unless the patient is unable to manage the pain, or unless there are signs of infection or obstruction.¹

Surgical

• Approximately 1 in 5 stones will not pass spontaneously and will require some form of intervention.
• If the stone is small and proximal, shock wave lithotripsy may be used to break the stone into smaller pieces, larger stones may be removed using ureteroscopy.
• Distal stones similarly may be removed using either lithotripsy or ureteroscopy.

Recurrence of renal stones is common and therefore patients who have had a renal stone should be advised to adapt several lifestyle measures which will help to prevent or delay recurrence:

• Increase fluid intake to maintain urine output at 2-3 litres per day.
• Reduced salt intake.
• Reduced amount of meat and animal protein eaten.
• Reduced oxalate intake (foods rich in oxalate include chocolate, rhubarb, nuts).
• Drink regular cranberry juice: increases citrate excretion and reduces oxalate and phosphate excretion.
• Maintain calcium intake at normal levels ( lowering intake increases excretion of calcium oxalate).