Orotic Acid on OAT and Ammonium

[Aaron Hartman]

You mentioned Orotic Acid being a marker for ammonium excess. I have a patient who consistently has normal orotic acid levels but on Amino Acid UAA testing has high ammonium levels (94800 [nl 16000-75000). Could you help me to understand the disparity with this?
Thanks
Aaron Hartman MD

[DrWoeller]

Dr. Hartman,
Direct measurement of ammonia is going to be more accurate for ammonia issues than orotic acid, although the orotic acid when high does indicate an ammonia build-up problem – specifically linked to the urea cycle.

What happens is carbamoyl-phosphate (a compound linked to ornithine transcarbamoylase deficieny) is converted to orotic acid. This leads to excess serum ammonia (and likely urine ammonia) and decreased BUN. The hyperammonia can deplete alpha-ketoglutarate leading to Kreb Cycle inhibition and decreased production of ATP.

How urine ammonia correlates to serum ammonia I don’t know specifically, other than individuals with kidney disorders may have a difficult time regulating ammonia.

Have you checked serum ammonia on this individual?

Dr. Woeller

P.S. One thing about amino acid tests in general, from my understanding, is the potential for degradation of the sample leading to inadvertent ammonia build-up.

[Aaron Hartman]

She has not had a serum ammonium level done to date.

With a normal orotic then the NH4 could be from product degradation. Interesting.

[DrWoeller]

Dr. Hartman,
From the looks of the amino acid they give it a good specimen viability rating. It’s always possible for degradation. I think with Orotic acid there needs to be significant dysfunction. I don’t see it elevated that often, and when it is it is just mildly high. Therefore, it is more of an indirect measurement I believe and getting ammonia checked itself is best.

Dr. Woeller

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