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Nephrolithiasis: what we all know as “kidney stones”- basic information.

What are “kidney stones”?

Kidney stones are hard and solid pieces of material that look like pebbles and form in one or both kidneys when there is a high concentration of certain minerals in the urine.

What size are they?

Kidney stones vary in size and shape; they can be as small as a grain of sand or as large as a pea. Rarely, some kidney stones are as large as golf balls. Kidney stones can be smooth or serrated and are usually yellow or brown in color.

How are they formed?

The kidneys have the ability to dispose of useless substances and salts, which need to be removed from the body, through the urine. Under normal circumstances said substances are dissolved and easily excreted. Sometimes, however, under certain conditions, these salts form crystals. Their continuous deposition in the kidneys creates larger crystals and, gradually, “stones”.

What problems can they cause?

When a kidney stone passes from the kidney to the ureter (the tube that connects the kidney to the bladder), it causes little to no pain if it is very small in size and does not cause an obstruction. A larger kidney stone, however, can get stuck along the way and block the flow of urine, causing severe pain (known as colic) or bleeding.

How common are they?

There are many patients with nephrolithiasis, and that number is constantly increasing. Approximately 11% of men and 6% of women in the United States will suffer from kidney stones at least once in their lifetime. It is the third most common urinary tract condition in humans, after urinary tract infections and prostate diseases.

What types of kidney stones are the most common?

There are different types of kidney stones that can be categorized based on their chemical composition.

  • Calcium is the most common component of kidney stones. Calcium stones occur more frequently in men aged 20-30 years. This element combines with other substances, such as oxalate and phosphorus, to eventually form a stone. However, calcium received from food does not increase the chances of developing calcium oxalate stones. Normally, the extra calcium that is not used by the bones and muscles goes to the kidneys and is flushed through the urine. When this does not happen, calcium remains in the kidneys and binds to other waste products to form kidney stones.
  • A uric acid kidney stone can form when our urine contains too much uric acid. Eating lots of fish, shellfish, and meat - especially organ meats (offal) - can increase uric acid in the urine. Usually, however, the risk of developing this type of kidney stone increases in patients undergoing chemotherapy. Uric acid stones are more common in men than women.
  • Struvite kidney stones usually form in women suffering from a urinary tract infection. These stones can become very large in size and form relatively quickly.

Who is most at risk for developing nephrolithiasis?

Men generally have a threefold increased risk of nephrolithiasis compared to women, as well as those with a family history of nephrolithiasis and those who do not consume enough fluids.

People with specific pathologies:

  • “Obstruction” in the normal flow of urine;
  • Hypercalciuria: a condition in which there is a high concentration of calcium in the urine;
  • Hyperoxaluria: unusually high amounts of oxalate in the urine;
  • Obesity;
  • Hyperparathyroidism;
  • Recurrent urinary tract infections.


  • Particularly increased amounts of animal albumen and fat in our diet;
  • Increased salt consumption;
  • Liquid consumption <1-1.5 liters in 24 hours.

By the Scientific Director Aristides Paraskevopoulos


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