The incidence of kidney stones is rising worldwide, especially with increasing age and among women. The risk of developing a kidney stone has now risen to between 10 and 15 percent and is trending higher. A probability of stone formation after an initial episode is 20 to 50 percent for the next ten years. Some contributing factors for kidney stones are insulin resistance, obesity, gastrointestinal and absorption problems, and specific diets and medications.
The pain of a kidney stone is extremely severe. It starts with sudden pain and cramping, usually in the flank, as the stone begins to travel slowly down the urinary tract. There can be nausea, vomiting, fever, chills and blood in the urine. Stones located in the middle of the renal pelvis may not have symptoms, but urine will be abnormal and sometimes testing may show impaired kidney function.
The types of stones and their composition depend on many factors. The most common type is calcium oxalate, making up about 60 percent of all stones. Calcium phosphate makes up another 10 to 15 percent. Cystine stones—the third most common type—may have genetic factors as a cause.
Geography plays a significant role in stone formation. High temperature and high humidity are contributing factors, and indeed hot summer months are the most common time for presentation of stones.
Diagnosing a stone is quite easy when the presenting pain in the flank area is sharp and associated with nausea and vomiting. Most affected individuals are unable to find any comfortable position to relieve the pain, which may be migratory as a stone works it way down from the kidney through the ureter and into the bladder.
Examination of urine will show blood on most occasions, and a stone that is passed should be analyzed to determine its composition. X-rays and ultrasound can demonstrate a stone’s composition, particularly when calcium based (which is radio-opaque).
Uric acid may also be a culprit for stone formation. Affected individuals may either over-produce uric acid or they may have too much uric acid in their bloodstream. This may eventually lodge in a spot in the kidney’s delicate filtration tubules and begin to form a stone. Uric acid is radiolucent and not seen on x-rays, so ultrasound is important in making the diagnosis for these cases.
Recurrent stones pose problems (besides the obvious pain and discomfort that accompanies them) when they obstruct the kidney and prevent normal urine flow. The backup not only distorts parts of the urinary tract with urine, but can compress and eventually cause renal failure if allowed to collect and form recurrently. Large stones may form in the pelvis of the kidney (staghorn calculi) and may have to be removed surgically to prevent permanent renal compromise.
Stones have the worst prognosis when they are bilateral, recurrent and/or lodge in the kidneys and are unable to be passed (staghorn). Medication, such as thiazide diuretics for calcium stones, allopurinol and dietary changes for uric acid stones, and increased fluid intake in almost all types of stones work effectively to avoid long term complications and, therefore, standard and preferred ratings are available in most cases.
