Hyperammonemia and Ornithine Transcarbamylase Deficiency after Bariatric Surgery: A Retrospective Study

Background: The number of bariatric surgeries has risen in the past decades. Hyperammonemia related to ornithine transcarbamylase (OTC) deficiency is a potentially lethal disorder in patients with neurological symptoms. The apparent prevalence of OTC deficiency and potential predictors of mortality was examined in patients after bariatric surgery. Methods: This is a retrospective study of postoperative patients who developed hyperammonemia in a large, urban teaching hospital. Urinary orotic acid levels were ordered in individuals with elevated plasma ammonia. Results: Between January 2012 and August 2017, 1597 bariatric surgical procedures were performed. Seven women hospitalized with consistent symptoms had a mean peak plasma ammonia level of 155 umol/L (range: 57 to 273) and mean urinary orotic acid excretion of 3.3 mmol/mol creatinine (range: 1.6–7.9) after vertical sleeve gastrectomy, duodenal switch, or gastric bypass surgery, and there were four mortalities (57%). The apparent postoperative prevalence of OTC deficiency is 0.31%. Peak lactic acid (p = 0.011) level is a predictor of mortality. Conclusions: Hyperammonemia is associated with a high mortality rate predicted by high lactic acid levels. Postoperative prevalence of OTC deficiency is higher than the general population. Further investigations should examine potential mechanisms for its development.