Excessive excretion of oxalate in the urine can predispose the patient to the formation of oxalate stones. If a patient with kidney stones has hyperoxaluria then the cause needs to be identified so that excretion can be reduced, if possible.


Definition of hyperoxaluria: > 45 mg per day (> 0.5 mmol per day)


Molecular weight of oxalic acid: 90.04 grams


General causal groups resulting hyperoxaluria:

(1) inherited metabolic disorders

(2) increased absorption due to enteric disease

(3) increased dietary intake

(4) intake of chemicals metabolized to oxalate


Inherited causes of increased excretion:

(1) primary hyperoxaluria (autosomal recessive)

(2) oxalosis (autosomal recessive)


Enteric diseases associated with increased absorption:

(1) Crohn's disease

(2) ileal bypass

(3) short bowel syndrome

(4) low calcium intake (oxalate intake is inversely proportional to calcium intake)

(5) bacterial decolonization of the gut (related to elimination of Oxalobacter species, which degrade dietary oxalate; decolonization results in more oxalate being available for absorption)


Dietary sources of oxalate:

(1) tea

(2) chocolate

(3) spinach

(4) rhubarb

(5) beets

(6) nuts

(7) wheat bran

(8) strawberries

(9) soy products


Chemicals or drugs metabolized to oxalate:

(1) vitamin C

(2) ethylene glycol (unlikely to be a chronic cause)

(3) methoxyflurane (unlikely to be a chronic cause)


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