Epidemiology of Kindey Stones
Prevalence: very common, somewhere between 12 - 20% in males and 5-10% of females
Age Distribution: peak 18- 45 years
Gender ratio: Male to female is 3:1
Recurrence rates: 40% in 2-3 years. 55% in 5-7 years, 75% in 7-10 years, 100% in 15-20 years
Types of Kidney Stones
There are only four possiblities. Calcium oxalate stones ccur 70-80% of the time, struvite (infection) stones in 10%, urate stones in 10-15%, cystone stones <1%. Extremely rare are trimaterene and indinivir stones that occur in HIV patients. There are a number of factors that conitibute
This is the most common stone. They are formed in the urine after supersaturation with calcium, oxalate, or phosphate. The risk factors of developing these stones are hypercalciuria (hyperparathyroidism), hyperuricosuria, hyperoxaluria, deficiency of inhibitors (citrate or nephrocalcitonin), low urine output, or high sodium intake. High sodium intake begets a high calcium exceretion which then causes hypercalciuria which leads to stones. High Hyperuricosuria is not associated in this case with urate stones but rather it is associated with increased occurce of calcium oxalate and calcium phospahte stones for unclear reasons.
Why stones form
Kidney stone events require the production of salid phase (crystals) of calcium oxalate, calcium phosphate, uric acid, struvit, cystine, etc. There is a relationship of the concentration of the dissolved salt in the urine divided by the solubility in the urine. The more soluble the more can fit in the urine. The concentration of dissolved salt depends on the urine volume and the solubility in the urine depends on pH and the temperature. The amount of fluid a person drinks or does not drink can change the concentration. When this concentration gets to a certain point, called super saturation, there is growth of pre-formed crystals or de novo cystals. So why doesn't everyone develop kidney stones? Well, there are a number of reasons for that. Most people drink lots of fluid so there is lower urine concentration and higher volumes. A very acid urine pH makes some crystals insoluble and an alkaline pH makes them more soluble. Urine also has naturally occuring inhibiors of crystal formation in the urine. The relationship between the inhibitor and the amount fo the type of crystals determines the likelyhood of developing stones.
(Concentration of dissolved salt) / (Solubility in the urine ) = Super Saturation
Spiral, unenhanced, non contrast CT scans is the single best imaging test to look for kidney stones. You are able to look at the entire urinary tract and so you can see other causes of flank pain. CT scanning allows visualization of all four types of stones in the collecting system down to 1 millimeter sized stones. IVP And KUB x rays are not this specific. Ultrasound is even worse.