This may be a really dumb question but please bear with me.
I have been reading some older posts and it seems that many people think that the various lab tests done for suspected metabolic disorder can either be normal or abnormal in a child who does in fact have disease.
So if this is so how do you even know or suspect something is wrong? Overall picture?
So the plan was to test him initially with an overnight fast and if that was normal we would test again when he was ill and if that was normal one more time if I recall also when ill. The idea was to catch the body under stress. He did tell me that my son had a lot of markers for metabolics (Andrew was really sick when we saw him/he was 3.5 at the time and had been in decline since about 18 months to 2 years) that he planned to treat him even if all those labs were normal to see if he responded to treatment. Andrew's initial labs were really abnormal so I don't know how all that would have played out in reality.
I don't know if other metabolic things show up better in the metabolic profiles. It's very possible they do (as most are included in newborn screenings for example) and mitochondrial is a special case. I don't know!
I can say that for some things like carntine deficiency (which we had) that's not going to fluctuate from day to day.
Rachelle, mommy to 8 year old boys!
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My son is one of the weird ones that has funky labs in a not typical mito fashion. He usually has lactic alkalosis (much more common in mito to have lactic acidosis) although in looking over his old labs recently, his was elevated once. We do standing labs every 3 months and you never know what you're going to get. One lab his 3-methylglutaconic acid was elevated (but glutaric was not), then another was elevated serine, theorine, and tryptophyn. They all are just really different for him. Until the elevated 3-MG, nothing in particular said "hey this kid has mito!" So had we just done blood and urine tests we may not have known what was going on till he was over 3 yrs old. We actually did the muscle biopsy hoping to rule out mito and instead that was his diagnosis.
It depends on the metabolic disease one has. Certain metabolic diseases always have wonky labs. Some meta diseases (like VLCAD) only have labs that are abnormal when the person is ill with a virus or has fasted to long, etc. And some diseases like Mitochondrial disorder, can be variable depending on the patient and the type of mito that child has (there are many different types).
So in a case where nothing is showing up but a doctor suspects a metabolic disorder anyway, based on symptoms, the doctors will usually try to draw "sick labs" and they may do a skin or muscle biopsy.
ETA: The doctors would usually suspect a metabolic disease based on the patient's symptoms. Not sure if I was clear with that.