The two most common defects in fatty acid metabolism are systemic primary carnitine deficiency and medium-chain acyl-CoA dehydrogenase deficiency or MCAD [FA2020 p89]. Both can present with physically normally appearing babies as the primary issues occur later (MCAD between 3 and 24 months and some variations of carnitine deficiency don't present until adolescence). Often the main danger is "hidden" in neonates unless prolonged fasting occurs because the individuals will go into hypoketotic hypoglycemic and can die. Thus, they are put on the newborn screens along with other disorders of fatty acid metabolism.
Thus, this neonate would have likely normal appearing physical exam and general labs. The best test of the list would be to look at acylcarnitine concentrations, which can be used to detect many disorders of fatty acid metabolism and some organic acidemias (https://neurology.testcatalog.org/show/ACRN)
Amino acids are not associated with fatty acid metabolism. ABG and electrolytes would likely be normal and would not be helpful in diagnosis. Lactic acid levels would be useful in neonates to give an idea of oxygen delivery to tissues, but is not useful here.
solidshakeJust adding to comment above
In the setting of a suspected defect in fatty acid oxidation, test for carnitine to find the cause:
If carnitine is low/absent -> primary carnitine deficiency
If carnintine is present/normal -> MCAD (deficiency with acyl-coa-dehydrogenase)
A big flag that you are in this scenario is an infant with Hypoketotic Hypoglycemia (characteristic of both diseases)+1
sexymexican888Just to add to this on how to differentiate MCAD from primary carnitine deficiency: (1) Primary carnitine deficiency: muscle weakness, cardiomyopathy, hypoketotic hypoglycemia, inc. muscle trygicerides.
(2) MCAD: hypoketotic hypoglycemia +1
submitted by โcassdawg(1780)
The two most common defects in fatty acid metabolism are systemic primary carnitine deficiency and medium-chain acyl-CoA dehydrogenase deficiency or MCAD [FA2020 p89]. Both can present with physically normally appearing babies as the primary issues occur later (MCAD between 3 and 24 months and some variations of carnitine deficiency don't present until adolescence). Often the main danger is "hidden" in neonates unless prolonged fasting occurs because the individuals will go into hypoketotic hypoglycemic and can die. Thus, they are put on the newborn screens along with other disorders of fatty acid metabolism.
Thus, this neonate would have likely normal appearing physical exam and general labs. The best test of the list would be to look at acylcarnitine concentrations, which can be used to detect many disorders of fatty acid metabolism and some organic acidemias (https://neurology.testcatalog.org/show/ACRN)
Amino acids are not associated with fatty acid metabolism. ABG and electrolytes would likely be normal and would not be helpful in diagnosis. Lactic acid levels would be useful in neonates to give an idea of oxygen delivery to tissues, but is not useful here.