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You are asked to evaluate a 3 day old male with severe lethargy and hypotonia. He is mildly tachypneic. He is afebrile. As part of your work-up, you evaluate him for inborn errors of metabolism. Which of the following is false about urea cycle disorder as a diagnosis for his findings?
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December 3, 2019 at 12:23 pm
A) An ammonia level of 100 micromol/L supports the diagnosis
Urea cycle disorders are a defect in ammonia metabolism. Infants can have an ammonia level of 100 micromol/L normally. Infants with urea cycle disorder should have a level > 250-500, and often have an even higher level. The most common urea cycle disorder is ornithine transcarbamylase deficiency. Newborns typically present on day 2-3 of life, but depending on the degree and type of enzyme deficiency, patients can present at older ages. Symptoms include headache, vomiting, altered mental status, seizures. Hyperventilation often occurs from cerebral edema, causing respiratory alkalosis. Protein intake must be stopped, and patients should receive dextrose at 8-10 mg/kg/min to reduce catabolism and promote insulin release. Ammonul, a combination of sodium phenylacetate and sodium benzoate, which act as nitrogen scavengers, should be administered. Very high ammonia levels may require emergent hemodialysis. An expert in genetic metabolic diseases should be consulted.