Table 2.

Diagnostic evaluation and interpretation of laboratory profiles

Simplified ambulatory metabolic evaluation	Extensive ambulatory metabolic evaluation	Expected daily values	Results interpretation
Random 24-h urinary profile	Random 24-h urine profile and 24-h urine profile after 1 wk of dietary restrictions
Total volume	Total volume	≥2.5 liter	Indicative of daily fluid intake. This value diminishes with low fluid intake, sweating, and diarrhea
pH	pH	5.9–6.2	Values < 5.5 increase UA precipitation. Commonly found in UA stone patients, subjects with intestinal disease and diarrhea, and in those with intestinal bypass surgery. Values > 6.7 increase CaP precipitation. Commonly found in patients with dRTA, primary hyperparathyroidism, alkali overtreatment, and carbonic anhydrase treatment. Values > 7.0–7.5 indicate a urinary tract infection as a result of urease-producing bacteria
Creatinine	Creatinine	15–25 mg/kg body weight	15–20 mg/kg body weight in females; 20–25 mg/kg body weight in males
Sodium	Sodium	100 mEq	Reflective of dietary sodium intake, given a lack of excessive sweating and/or diarrhea
Potassium	Potassium	40–60 mEq	Reflective of dietary potassium intake, given a lack of diarrhea
Calcium	Calcium	≤250–300 mg	There may be differences in male and female subjects. A higher value is expected in males
Magnesium	Magnesium	30–120 mg	Low urinary magnesium is detected with low magnesium intake, intestinal malabsorption (small bowel disease), and after bariatric surgery
Oxalate	Oxalate	≤45 mg	Commonly encountered with intestinal fat malabsorption and after bariatric surgery. Values > 100 mg/d may indicate primary hyperoxaluria
Phosphorus	Phosphorus	≤1100 mg	Indicative of dietary phosphorus intake and absorption. A higher excretion may increase the risk of CaP stone formation
UA	UA	600–800 mg	Hyperuricosuria is encountered with the overindulgence of purine-rich foods such as red meat, poultry, and fish
Sulfate	Sulfate	≤25–30 mmol	Sulfate is a marker of an acid-rich diet that occurs as a result of increased oxidation of sulfur-rich amino acids (methionine) found in meat and meat products
Citrate	Citrate	≥320 mg	An inhibitor of calcium stone formation. Hypocitraturia is commonly encountered in metabolic acidosis, dRTA, chronic diarrhea, excessive protein ingestion, strenuous physical exercise, hypokalemia, intracellular acidosis, with carbonic anhydrase inhibitor drugs (acetazolamide, topiramate, and zonisamide), and rarely with ACE-inhibitors
Ammonium	Ammonium	30–40 mEq	Ammonium is a major buffer that neutralizes hydrogen protons secreted by the kidney. Its excretion corresponds with urinary sulfate (acid load). A higher ammonium:sulfate ratio indicates gastrointestinal alkali loss
Chloride	Chloride	100 mEq	Chloride values also correspond with sodium intake
Cystine	Cystine	<30–60 mg	Cystine has a limited urinary solubility at 250 mg/liter
	2-h fasting Ca:Cr ratio	<0.11 mg/100 ml glomerular filtrate	Elevated fasting Ca:Cr, high serum calcium, and elevated PTH are suggestive of primary hyperparathyroidism. Elevated fasting Ca:Cr, normal serum calcium, and normal or suppressed PTH are suggestive of resorptive hypercalciuria. Elevated fasting Ca:Cr, normal serum calcium, and elevated PTH are suggestive of renal hypercalciuria
	4-h Ca:Cr ratio after a 1-g oral calcium load	≤0.20 mg/mg Cr	Elevated Ca:Cr after a 1-g oral calcium load is suggestive of absorptive hypercalciuria
Simplified fasting blood chemistries	Extensive fasting blood chemistries
Complete metabolic panel	Complete metabolic panel	Variablea	Low serum potassium, high serum chloride, and low serum total CO2 content are suggestive of a diarrheal state of dRTA
PTH	PTH	10–65 pg/mla	High serum calcium, low serum phosphorus, and high PTH are suggestive of primary hyperparathyroidism
	1,25(OH)2D	Variablea	Normal serum calcium, normal PTH, and elevated 1,25(OH)2D are suggestive of absorptive hypercalciuria. Normal serum calcium, normal PTH, low serum phosphorus, and elevated 1,25(OH)2D are suggestive of renal phosphorus leak
	Other evaluations
	Bone mineral density measurements (DXA)	Z-score > −2; T-score > −2.5	Z-score < −2 or T-score < −2.5 indicates bone loss. This finding may be more prevalent in hypercalciuric kidney stone formers

These limits are mean + 2 sd (for calcium, oxalate, UA, pH, sodium, sulfate, and phosphorus) or mean − 2 sd (for citrate, pH, and magnesium) from normal. ACE, Angiotensin-converting enzyme; DXA, dual-energy x-ray absorptiometry.

^aExpected values should be cross-checked with reference laboratory recommendations because these values may differ.