Kidney stones, also known as urolithiasis, are a common affliction of the urinary tract. Depending on the location of the stone in your urinary tract, the stone may be referred to by different names.
A stone in your kidney is called a renal calculi or nephrolithiasis. A ureteral calculus or ureterolithiasis is a stone in one of your ureters, the tubes that connect each kidney to your bladder.
Types of Kidney Stones
There are four major types of kidney stones: (1) calcium stones, which are the most common type, are primarily composed of calcium and either phosphate or oxalate, and are primarily due to increased calcium levels in urine; (2) urate or uric acid stones, which are smooth, soft and brown stones that form because of increased uric acid levels in urine; (3) struvite stones, which contain magnesium and ammonia and are typically formed because of infectious bacteria that split a chemical called urea; and (4) cystine stones, which are yellow and are caused by a relatively rare metabolic condition.
When a kidney stone reaches a certain size, usually 2-3 mm, it can cause blockage of the normal flow of urine from the kidneys to the bladder and out of the body. This blockage causes dilation and muscle spasm, causing pain in a patient's side, lower abdomen or groin. If a kidney stone does not pass spontaneously and is not treated, patients experience a significant amount of pain and eventually damage to the urinary tract.
Stone formation is a complex process. It begins with urine developing a higher concentration of certain salts than is normal. These salts pop out of the liquid urine to form crystals. Crystals can flow out with urine, or become attached at various sites in the kidney. Eventually crystals accumulate at an attachment site to form a stone.
Certain medications may increase your risk of developing kidney stones, such as aspirin, antacids, certain diuretics or "water pills", calcium and Vitamin D supplements, and anti-retroviral medications such as Indinavir.
Each type of kidney stone has specific factors that increase risk of their formation. The higher than normal levels of calcium in urine that can cause calcium stones could be due to an overactive parathyroid gland (hyperparathyroidism), high levels of Vitamin D, kidney disease, sarcoidosis or some cancers.
Uric acid stones can form when your urine is very acidic, which can happen as a result of metabolic imbalances such as gout, chemotherapy, or a high protein diet. Struvite stones, which are more common in women than men, are always associated with urinary tract infections. The bacteria causing these infections release a protein that lowers the acidity of urine, allowing struvite stones to form. Cystine stones are caused by an inherited condition called cystinuria, which affects how much acid is excreted in your urine.
Because the risk of having a kidney stone is increased if you have previously had one, prevention is very important. Preventative strategies include dietary modification and some drugs, depending on the cause of your stone. These strategies specifically may include:
- Drinking plenty of fluids. Normally, you should drink at least 6 to 8 glasses of water a day, but in the special case of having a kidney stone, you should increase this to 2-3 liters a day!
- Reduce the protein, nitrogen and sodium in your diet
- Restrict oxalate-rich foods such as chocolate, nuts, soybeans, spinach and rhubarb
- Maintain adequate calcium intake
- Certain fruit juices such as orange, cranberry and blackcurrant juice may reduce the risk of specific stones (orange – calcium oxalate, cranberry – struvite, blackcurrant – uric acid)
- Avoid cola beverages
- Avoid large amounts of vitamin C
- Drugs such as thiazide diuretics, allopurinol, potassium and magnesium citrate, depending on the type of stone