A General Approach to Inborn Errors of Metabolism

A General Approach to Inborn Errors of Metabolism 

Kate Billings, MD


Case: A 7-year-old girl is brought to the ER by her mom for vomiting. Her mom states she has vomited 5 times this morning and hasn’t been tolerating PO intake. The girl’s brother recently had a “24-hour stomach bug” per mom. Within the past hour, the girl has been difficult to arouse and mumbling random words. Mom says she has a history of S-CAD.  

Physical Exam – BP 82/60; HR 124; Temp 37.4; RR 32 

General: Lethargic appearing, but arousable to vocal stimulation. 

Cardiac: Tachycardic, regular rhythm, no murmurs 

Pulmonary: Lungs are clear to auscultation bilaterally; no respiratory distress. 

Abdominal: Soft with mild generalized tenderness  


What is S-CAD? S-CAD, also known as Short-chain acyl-CoA dehydrogenase, is one of the many inborn metabolic disorders that can be seen in pediatric patients.  

There is a seemingly endless number of inborn errors of metabolism, and many of these children can present acutely to the emergency room. Many emergencies in these patients are triggered by dehydration, such as vomiting in the case above. This leads to a catabolic state in these patients.  


Below is a general outline on how to approach most inborn errors of metabolism and general guidelines for resuscitation (besides the usual ABCs, IV, O2, monitor) 

  1. Glucose! This should be obtained immediately upon arrival. 

  1. Many of these patients will be hypoglycemic and need intervention. 

  1. Rehydration. Dehydration often caused the catabolic state.  

  1. IVF should be started right away. A general rule is to give D10 ½ NS at 1.5 times the maintenance rate.  

  1. Ammonia level. These patients can have elevated ammonia levels secondary to catabolic pathways. *Should be drawn free flowing* 

  1. Treatment can be with sodium benzoate or sodium phenylbutyrate  

  1. Electrolytes, VBG, ketones, lactate. 

  1.  These patients often can have significant acidosis, ketosis, and electrolyte abnormalities that need to be corrected. 

  1. Other important labs to draw (won’t result in the ER): plasma amino acids and urine organic acids. 

  1. Consult a metabolic geneticist for further management and transfer decisions. 

  1. Most importantly: talk to the parents. They often have a written treatment plan given to them by their child’s metabolic doctor. It will provide the steps necessary to treat this child’s specific disorder emergently. 



MacNeill EC, Walker CP. Inborn Errors of Metabolism in the Emergency Department (Undiagnosed and Management of the Known). Emerg Med Clin North Am. 2018 May; 36 (2): 369-385.