Kidney stones are accumulations of crystals that pass from the bladder through the urethra. Small stones are common and are usually passed in urine without incident. However, stones over 2mm in diameter can cause obstruction of the urethra, leading to decreased or blocked flow of urine accompanied by extreme pain and distension of the bladder until the stone passes. The stone can be formed of several different types of materials, but most are some form of calcium compound. They are very common, occurring in 10-15% of the population in the United States. They are more common in hot, dry countries.
Several conditions can lead to the accumulation of crystals in the bladder that lead to stone formation, such as renal tubular acidosis and Crohn's disease. People suffering from stones should be screened for all the diseases that are associated with them. Stones can be seen with x-rays, ultrasound, or a CT Scan, and can also be confirmed through testing the urine or blood.
The vast majority of stones will pass without medical intervention, and the remainder usually only require encouragement of urination, such as drinking more water. Pain control is an important part of treatment. Surgery to remove a stone is rare and is generally only considered when the stone is accompanied by an infection or has not passed after a few days. As such, treatment is focussed on prevention. A patient who suffers from kidney stone formation will generally be treated by:
- Being told to drink more water to prevent crystal formation;
- Avoiding high-protein, high-nitrogen and high-sodium foods, which encourage crystal formation.
- Avoiding foods high in oxalates - e.g. nuts, chocolate, spinach, rhubarb.
- Avoiding certain medications which can form stones.
- Drinking more juices - e.g. orange, blackcurrant and cranberry.
- Avoiding caffeine.
Struvite stones
This is a description of a certain type of kidney stone where the crystals are made from the breakdown of urea by bacteria. They usually indicate that the patient also has a urinary tract infection. This was a suggested differential in the episode Frozen.