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What is a Kidney Stone? Renal Calculus, Size and Types of Stones

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A kidney stone, also known as a renal calculus (plural ~ calculi), are crystal aggregates that form within the kidney. A stone or stone(s) will pass down the ureter and enter the bladder. Due to its passage through the urinary system, kidney stones may also be called urinary stones or the term nephrolithiasis is used to refer to the presence of kidney stones.

The term ureterolithiasis refers to stones in the ureter(s) – usually stones form in the kidneys but grow further in the ureter, where they cause the most notable pain. Some stones may pass out with the urine while others will require medical intervention like surgery or ultrasound ‘shock waves’ or laser ‘blasting’.

There are a number of causes of kidney stones but in most cases the formation of the kidney stones are the same. A high concentration of certain substances within the urine will cause precipitation. With time these substances aggregate and a kidney stone is formed. It may continue growing further while it passes through the rest of the urinary system.

Size of Kidney Stones

The size of kidney stones may vary in size – calculi can be small like fine sand or large round stones may be found in the bladder. Stones that are 2 to 4 mm may pass out with much pain while stones larger than 5 to 6 mm can result in obstruction and require intervention. Frequent stones or those as large as 7mm to 8mm can result in serious complications.

The most common symptoms of kidney stones include kidney pain, pain from the flanks to the groin, pain upon urination (dysuria),  nausea, vomiting, changes in urine color or blood in the urine (hematuria). Less frequently, a fever and chills may be present.

Types of Kidney Stones

Most kidney stones contain calcium but other compounds, particularly the breakdown products of proteins, may also form kidney stones. The types of crystals that give rise to kidney stones are listed below  in order of prevalence.

  • Calcium oxalate (sometimes calcium phosphate)
  • Magnesium ammonium phosphate (struvite)
  • Urate/uric acid
  • Hydroxyapatite
  • Brushite
  • Cystine
  • Mixed stones

Shape, Color of Stones

  • Calcium oxalate- spiky, uneven jagged, brown.
  • Calcium phosphate – smooth.
  • Struvite – staghorn, tan color.
  • Urate – smooth, brown.
  • Cystine – yellow crystalline.

Article reviewed by Dr. Greg. Last updated on May 27, 2010