Calcium: the majority of stones have calcium in them. Calcium oxylate is the most common, but calcium phosphate is seen too. Think about hyperparathyroidism, other causes of hypercalcemia, medulary sponge kidney, low urine volumes, or chronic metabolic acidosis like in distal renal tubule acidosis (aka Type 1).Uric Acid: Seen primarily in patients with particularly acidic urine, like a pH less than 5.5 where uric acid precipitates out. This is seen most commonly in those with gout, but can be found in anyone with high uric acid production (eg myeloproliferative/lymphoproliferative disorders). Note: Plain X-ray is not helpful in the diagnosis as these stones are radiolucent. Treat with increasing urine volume, urine alkalinization, and allopurinol to lower uric acid production.
Struvite: caused by organisms that produce the enzyme urease (Proteus or Klebsiella). These may form really big stones, called Staghorn stones, and can fill collecting ducts. See the accompanying pictures. Ouch.
Cystine: Usually an autosomal dominant disorder where patients have cystinuria. A hexagonal cystine crystals may be seen on urinalysis. Treatment usually involves increasing fluid intake and alkalinization of the urine with an agent like potassium citrate.
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