Occasional vomiting is not a specific symptom for insulinoma.
 
Low blood glucoses can also be the result of lab error - if the blood is
not quickly processed, then the red blood cells may use the glucose for
energy, and the level goes down.  This continues until the blood is
processed.
 
If he has shown no evidence of hypoglycemia (staring, drooling, difficulty
walking, seizures, etc.), and is still full of energy, I would strongly
recommend rechecking that blood test.
 
With kindest regards,
Bruce H. Williams, DVM, DACVP
 
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[Posted in FML issue 3419]