Nitrogen, derived from breakdown of dietary amino acids as ammonia, is normally converted to urea and excreted. Impairment in the conversion process (called the urea cycle) can occur, either as a consequence of primary genetic defects or through secondary suppression of enzyme activity. Either process results in hyperammonemia, producing a clinical picture virtually indistinguishable from many other diseases of infancy. Moreover, there is no way to detect hyperammonemia except to measure the blood ammonia level. Thus, the capability to do so is a minimum standard of care in any hospital setting. Use of commonly obtained laboratory studies is discussed in the context of rapid, presumptive diagnosis of the causes of hyperammonemia.
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