Summary

• Amino acid disorders, called aminoacidopathies, are rare conditions that are usually inherited from your parents.
• These conditions cause problems with the way your body processes food.
• Amino acid testing is mostly used to investigate infants thought to have an aminoacidopathy.
• Treatment is usually through diet.
• Testing is also used to make sure treatment is working.

What are amino acid disorders?

Aminoacidopathies are a group of rare but treatable disorders in which the body has problems breaking down, processing, or transporting amino acids, the tiny molecules that join together to make proteins. Proteins are your body’s basic building blocks that it needs to function and grow.

The main use of amino acids is to make new proteins for building cells, muscles, enzymes, hormones and just about everything. When the body does not need to make more protein, amino acids are broken down for energy.

Your metabolism is the system your body uses for processing food to make energy and build tissue. This system uses enzymes to convert food into energy proteins to transport amino acids around the body. A metabolic disorder is when this process does not work properly, usually due to a faulty or missing enzyme or transporter protein.

Aminoacidopathies are almost always caused by gene mutations and are inherited – meaning you get them from your parents. Certain genes give instructions for making or transporting amino acids. When one of these genes has a mutation, and the genetic instructions are faulty, amino acids or their by-products can build-up to toxic levels, affecting normal growth, development and organ function.

More than 30 aminoacidopathies are known about and examples include phenylketonuria (PKU), maple syrup urine disease (MSUD) and homocystinuria.

Almost all aminoacidopathies are inherited, but a few are not caused by gene mutations and can occur because of medical problems such as liver failure, severe infection, starvation or toxin exposure.

Why get tested?

Amino acid testing is mostly used to investigate infants thought to have an aminoacidopathy. It is also used for monitoring treatment.

Reasons for amino acid testing include:

• failure to thrive (where a baby is not growing as fast as it should)
• recurrent vomiting
• lethargy
• high levels of ammonia in the blood
• metabolic acidosis (when blood pH falls below the normal range due to having too much acid in the body)

Most metabolic disorders present early in life although milder forms can go undetected until adulthood.

With early diagnosis and treatment, symptoms can be minimised or prevented. Treatment is usually based on having a special diet.

Regular testing is used to help monitor treatment to make sure amino acid levels stay under control and nutrition is adequate for growth and development.

Newborn bloodspot screening or heel prick test

The newborn blood spot screening is a test done on all babies born in Australia. When the baby is born, drops of blood are collected and testing is done to identify if they have one of a range of conditions including aminoacidopathies. The blood is collected by pricking the baby’s heel which is why it is sometimes called the heel prick test.

The results of this testing are returned very quickly so that any condition identified can be treated quickly to minimise any associated symptoms.

Having the test

Sample

Either blood or urine depending on the test.

Any preparation?

None.

Your results

In amino acid testing all the amino acids that are made by the body or taken in from your diet are separated and measured. This makes it possible to see if the amount of any particular amino acid is high or low.

The measured levels are compared to established reference intervals (ranges for healthy people) so that any high or low concentrations can be identified.

Reference intervals for amino acids vary depending on the age of the person being tested and the type of amino acid. The laboratory performing the test will comment on any important findings.

Increased or decreased levels of certain amino acids can reveal a metabolic problem that has been caused by an aminoacidopathy. For example, increased glutamine may point to a defect in the urea cycle. Having normal amounts of amino acids does not rule out other inborn errors of metabolism.

Your results will be presented along with those of your other tests on the same form. You will see separate columns or lines for each of these tests.

Reference intervals - comparing your results to the healthy population

Your results will be compared to reference intervals (sometimes called a normal range).

• Reference intervals are the range of results expected in healthy people.
• They are used to provide a benchmark for interpreting a patient's test results.
• When compared against them, your results may be flagged high or low if they sit outside this range.
• Some reference intervals are harmonised or standardised, which means all labs in Australia use them.
• Others are not because for these tests, labs are using different instruments and chemical processes to analyse samples.
• Always compare your lab results to the reference interval provided on the same report.

If your results are flagged as high or low this does not necessarily mean that anything is wrong. It depends on your personal situation.

Questions to ask your doctor

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

More information

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.

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