Last update:
09-Mar-2009

Nephrolithiasis is a relatively common disease with a higher rate in the white race and in males. The main types of kidney stones are composed of calcium (80%) oxalate or phosphate, uric acid, struvite and cystine. Patients may be asymptomatic, or present with renal colic or atypical symptoms, or with complications (such as obstruction) that need to be managed by specialist physicians. In asymptomatic, first-time and single-stone formers, without residual stone or fragments, and in patients with mild disease, an abbreviated diagnostic evaluation may also be performed by non specialist physicians. This includes a focused history to assess the risk of further stone formation, radiographic imaging, urine tests, blood chemistry and, if available, stone analysis. The medical history may reveal a family history of stones and suggest an underlying condition (such as gout) or life-style risks (including patient's occupation, dietary habits, fluid consumption, intake of certain medications). Non-contrast helical computed tomography (CT) is the gold standard in radiographic diagnosis, and it may suggest the type of stones and the site and degree of obstruction. An intravenous pyelography, restricted during recent years because of contrast medium-related toxic effects, may identify urinary tract anatomical abnormalities and establish the diagnosis of medullary sponge kidney. An abdominal plain X-ray film and ultrasonography (US), the latter being an alternative in pregnant women, are useful in patient monitoring. Urine pH >7.5 is compatible with infection lithiasis whereas pH <5.5 favors uric acid lithiasis. Specific crystal types in urine sediment may provide clues as to stone composition. Hypercalcemia necessitates serum intact parathyroid hormone measurement for diagnosing primary hyperparathyroidism. A low plasma bicarbonate concentration is suggestive of distal renal tubular acidosis or chronic diarrhea. All available stones should be analyzed to determine their crystalline composition in order to select the appropriate treatment program. In groups at moderate to high risk, a more extensive metabolic evaluation by specialist physicians is recommended, with two or three 24-hour urine collections in the outpatient setting at least two or three months after a stone event. Hypercalcemia, hypercalciuria, hyperuricosuria, hyperoxaluria and hypocitraturia are possible underlying causes of stone disease. The decision for a complete evaluation, including 24-hour urine collections, should be shared by physicians and patient, because first time and recurrent stone formers have the same underlying risk factors and severity of stone disease.

Key words: Metabolic evaluation, Nephrolithiasis, Radiographic imaging, Renal colic, Stone composition.