Kidney Stones

Kidney stones (calculi) are hardened mineral deposits that form in the kidney. They originate as microscopic particles and crystals and develop into stones over time. The medical term for this condition is nephrolithiasis, or renal stone disease. The kidneys filter waste products from the blood and add them to the urine that the kidneys produce. When waste materials in the urine do not dissolve completely, crystals and kidney stones are likely to form. These stones may stay in the kidney for a long time or they may pass out of the kidney and become lodged in the tube that carries urine from the kidney to the bladder (ureter). If left untreated, the kidney may swell and lose its function.

Stone Formation

Kidney stones form when there is a high level of calcium (hypercalciuria), oxalate (hyperoxaluria), or uric acid (hyperuricosuria) in the urine; a lack of citrate in the urine; or insufficient water in the kidneys to dissolve waste products. The kidneys must maintain an adequate amount of water in the body to remove waste products. If dehydration occurs, high levels of substances that do not dissolve completely (e.g., calcium, oxalate, uric acid) may form crystals that slowly build up into kidney stones.

Urine normally contains chemicals-citrate, magnesium, pyrophosphate-that prevent the formation of crystals. Low levels of these inhibitors can contribute to the formation of kidney stones. Of these, citrate is thought to be the most important.


The four most common types of stones are comprised of calcium, uric acid, struvite, and cystine.

  1. Calcium stones
    Approximately 85% of stones are composed predominantly of calcium compounds. The most common cause of calcium stone production is excess calcium in the urine (hypercalciuria).
    Increased intestinal absorption of calcium (absorptive hypercalciuria), excessive hormone levels (hyperparathyroidism), and renal calcium leak (kidney defect that causes excessive calcium to enter the urine) can cause hypercalciuria. Prolonged inactivity also increases urinary calcium and may cause stones.
  2. Uric acid stones
    Digestion produces uric acid. If the acid level in the urine is high or too much acid is excreted, the uric acid may not dissolve and uric acid stones may form. Genetics may play a role in the development of uric acid stones, which are more common in men. Approximately 10% of patients with kidney stone disease develop this type of stone.
  3. Struvite stones
    This type of stone, also called an infection stone, develops when a urinary tract infection (e.g., cystitis) affects the chemical balance of the urine. Bacteria in the urinary tract release chemicals that neutralize acid in the urine, which enables bacteria to grow more quickly and promotes struvite stone development.Struvite stones are more common in women because they have urinary tract infections more often. The stones usually develop as jagged structures called “staghorns” and can grow to be quite large.
  4. Cystine stones
    Cystine is an amino acid in protein that does not dissolve well. Some people inherit a rare, congenital condition that results in large amounts of cystine in the urine. This condition (called cystinuria) causes cystine stones that are difficult to treat and requires life-long therapy.

Causes & Risk Factors

Several factors increase the risk for developing kidney stones, including:

  • Inadequate fluid intake and dehydration
  • Reduced urinary flow and volume
  • Certain chemical levels in the urine that are too high (e.g., calcium, oxalate, uric acid) or too low (e.g., citrate)
  • Medical conditions that block or reduce the flow of urine (e.g. urinary obstruction, genetic abnormality) also increases the risk.
  • Urinary tract infections
  • Diet – A diet high in sodium, fats, meat, and sugar, and low in fiber, vegetable protein, and unrefined carbohydrates increases the risk for renal stone disease. High doses of vitamin C (more than 500 mg per day) can result in high levels of oxalate in the urine (hyperoxaluria) and increase the risk for kidney stones. Oxalate is found in berries, vegetables (e.g., green beans, beets, spinach, squash, tomatoes), nuts, chocolate, and tea. Stone formers should limit their intake of cranberries, which contain a moderate amount of oxalate.

Signs & Symptoms

Small, smooth kidney stones may remain in the kidney or pass out without causing pain (called “silent” stones).

Larger stones may cause symptoms including:

  • Loin to groin pain – Stones that lodge in the tube that carries urine from the kidneys to the bladder (ureter) result in severe pain that begins in the loin and lower back and radiates to the groin or front of the lower abdomen.
  • Blood in the urine (hematuria)
  • Increased frequency of urination
  • Nausea and vomiting
  • Pain during urination (stinging, burning)
  • Tenderness in the abdomen and kidney region
  • Urinary tract infection (fever, chills, loss of appetite)


Diagnosis of renal stone disease involves a medical history, physical examination, laboratory evaluation, and imaging tests.

Laboratory Tests

  • Urinalysis to detect the presence of blood (hematuria) and bacteria (bacteriuria) in the urine.
  • Blood tests for Creatinine (to evaluate kidney function), Urea & Electrolytes (to detect dehydration), Calcium (to detect hyperparathyroidism), and a Full Blood Count (to detect infection).

Imaging Tests

Imaging tests used to diagnose kidney stones include:

  • Ultrasound
  • IVU (Intravenous Urogram)
  • CT scan (Computer tomography)


Small stones may move through the ureter and be passed out naturally with adequate fluid intake.

If a kidney stone does not move through the ureter on its own, surgery is considered. There are several options available, including:

  • ESWL (Extracorporeal shock wave lithotripsy)
  • URS (Ureteroscopic removal of stone)
  • PCNL (Percutaneous Nephrolithotripsy)
  • Open Surgery

This procedure requires general anesthesia. An incision is made in the patient’s back and the stone is extracted through an incision in the ureter or kidney. Most patients require prolonged hospitalization and recovery takes several weeks. This procedure is now rarely used for kidney stones.