Diagnosis methods for OTC deficiency

When a person expresses all the symptoms of OTC deficiency, he is first put through a initial test where the test is specific to OTC deficiency and several other conditions, therefore we do not say that it is a specific test. If the test results come back positive, a confirmatory test is then given to the patient to confirm that he has OTC deficiency. This test is far more specific than the initial test, however may require more sample from the patient.

One of this confirmatory test methods is the test for blood gases. The patient would be tested for respiratory alkalosis due to hyperammonemia, this would clearly distinguish that the patient has a urea cycle disorder compared to an organic acidemia.

An initial test that can be done to confirm OTC deficiency is the plasma ammonia concentration test. When a patient’s blood ammonia concentration is above 100 micromol/L. If this initial test comes back positive, the confirmatory test would be carried out.

This confirmatory test varies depending on the age group of the patient testes. In newborns, samples would be taken from the baby and run through plasma amino acid analysis to test the results of amino acid testing, the result expected would be high concentrations of glutamine and a low concentration of citrulline.

When the testing is done on anyone else except newborn babies, the same test can be repeated and the results of the test should be the same, which would conclude that this person has OTC deficiency. However there is another test that can be done to confirm that this person has OTC deficiency. This is the urine organic acid analysis, the results of the test for a OTC deficient patient should be that the orotic acid concentration would likely to be elevated. This method is more specific to OTC deficiency because it is one fo the few diseases that would cause this to happen.

When the patient has tests that come back as all positives, the doctors would put the patient through a final diagnosis which would confirm that he has OTC deficiency. This is a genetic test, and therefore would be very specific towards OTC deficiency. The first test is the identification of the pathogenic mutation in OTC, which is the only mutation which can cause OTC deficiency.

The next test that the doctors can use to confirm that this person has OTC deficiency is looking for decreased OTC enzyme activity in the liver, the exact numbers are <20% of control in severe cases of OTC deficiency and up to 30% of control in a milder case of OTC deficiency.

When a patient has all these tests turn up positive, there is a very high chance that he suffers from OTC deficiency, and the doctors can conclusively say that the patient is OTC deficient and should start medical care for the disease.

Sources: http://www.orpha.net/consor/cgi-bin/OC_Exp.php?Expert=664