Amino acid testing for depression, anxiety and other mental symptoms
Amino acid tests can help some people with depression, anxiety, or other mental symptoms.
However there is no cookie cutter protocol for "treating depression." As a naturopathic doctor I only believe in treating the person, not the disease. Every individual is different and the causes for mental symptoms vary greater from person to person. In fact, for most people who complain of depression or anxiety I don't even recommend amino acid testing. After taking a careful history these is usually something else more important to treat.
Factors which may contribute to mental symptoms include:
- Toxicity (ie. heavy metals, infections, candida, etc...)
- Emotional trauma
- Physical trauma (ie. head injury, spine subluxation, etc...)
Some people in the nutrition field tend to view mental illness (especially depression) as an amino acid deficiency problem. This may be true from some people, but not everyone. I hope that the information below helps people, but please use it with respect to the whole person and consider all factors relevant to the individual.
Amino acids introduction
Amino acids are the building blocks of proteins. Our muscles and organs are mostly made out of protein. Neurotransmitters are made from amino acids, and that's why they are often helpful for people with mental symptoms.
There are 9 essential amino acids. Our bodies can't make these on their own so we have to get them through our diet.
The nine essential amino acids:
Other amino acids which our bodies can manufacture are called "non essential." However, if we are deficient in protein, nutrients, dealing with excess toxicity or under stress, we can become deficient in non-essential amino acids as well.
Non-essential amino acids:
- Aspartic acid
- Glutamic acid
Factors which can lead to sub optimal levels of amino acids:
- Lack of protein in diet, either eating too little, or a poor vegetarian diet.
- Poor digestion
- Genetic factors
- Iatrogenic (side effect of medical treatment) 
In case of a deficiency ,amino acid supplements can help, but it's also important to find out what caused the deficiency and fix that problem as well.
Certain vitamin deficiencies may lead to high levels of amino acids on tests. The body may have the amino acids, but lack the vitamins necessary to use them.
Amino acid testing
Amino acid status can be tested in blood or urine. Generally blood is the preferred method to monitor status and guide supplementation. Urine is mostly used to detect genetic problems, nutrient deficiencies or toxicity related to amino acid status.
Sample amino acid test:
The above test shows low amounts of histidine, lysine and marginally low phenylalanine. Elevated tryptophan can be related to poor usage, or in this case supplementing with 5-htp.The following section will overview the amino acids generally most relevant with respect to mental symptoms.
We are always producing some ammonia as part of normal metabolism. Arginine is needed to remove ammonia from the body and insufficiency can lead to excess ammonia (hyperammonemia). 
Signs of excess ammonia:
- Anorexia (loss of appetite)
- Heavy or rapid breathing
- Somnolence (sleepy)
- Cerebral edema
Histidine is the precursor to histamine. Many people are familiar with the role histamine plays in triggering allergies. However, in the brain histamine functions as a neurotransmitter, especially in an area called the hypothalamus which regulates hormone production.
The diagram shows just a few of the many jobs histamine has:
If one process (such as an allergy) uses up a lot of histidine, this may leave less available for the brain and present as mental symptoms. Therefore, not only may supplementing with histidine make sense, but it's important to investigate why the body is using up all it's histidine. 
Phenylalanine and Tyrosine
Phenylalanine and tyrosine are precursors to both thyroid hormone, and three neurotransmitters.
Dopamine, norepinephrine and epinephrine (commonly known as adrenaline) make up a family of neurotransmitters called catecholamines. Catecholamines are needed for movement, memory, attention, problem solving, desire, motivation, the stress or "fight or flight" response, regulation of the cardiovascular system and energy production.
Deficiency of tyrosine (or nutrients needed to convert tyrosine to the catecholamines) may lead to: hypothyroidism, chronic fatigue, nervous system dysfunction, depression, impaired learning, memory and behavioral disorders including anxiety. 
The newer class of antidepressants, the SNRIs (serotonin norepinephrine reuptake inhibitors) in theory increase the levels of norepinephrine available to brain cells.
But doesn't it make more sense to give the body the amino acids and vitamins it needs, then to manipulate the brain with toxic medications?
In addition to testing amino acid levels, the production of dopamine, norepinephrine and epinephrine can be looked at on an organic acid test.
Tryptophan and 5-HTP
Tryptophan, and 5-HTP (5-hydroxy-tryptophan) are the precursors to serotonin.
Serotonin has been promoted as a feel good neurotransmitter related to depression. However, it has numerous functions:
- Most of it is (over 90%) is in the gastrointestinal system regulating digestion.
- Regulation of pain perception. Low levels of serotonin increase pain perception. This can contribute to chronic pain such as in classic fibromyalgia.
- Regulates sleep through conversion to melatonin. Melatonin is our sleep hormone. It is low during the day, then goes up at night so we can fall asleep.
Vitamin B6 and magnesium are also needed to convert tryptophan to serotonin. Signs of low magnesium include constipation, muscle cramps (especially calves and bottom of feet), and chocolate cravings (chocolate is relatively high in magnesium). Lack of dream recall sugests a need for vitamin B6.
GABA is a inhibitory neurotransmitter low in some people with mental symptoms such as depression or anxiety. GABA is available as a supplement. Vitamin B6 can also help the body make more on its own. 
Serine is the amino acid precursor for the neurotransmitter acetylcholine. Acetylcholine is important for memory, and the nervous system. Studies have also found a link between low serine levels and depression. 
Other tests for neurotransmitter status?
There are no tests which measure brain levels of neurotransmitters. Various blood or urine tests for neurotranmitters do not show what is going on in the brain.. Rather the results are used to infer brain biochemistry.
Hypothetically, even if a test was available to measure brain neurotransmitters was available the results could still be of limited value. For example, if someone felt depressed and a neurotransmitter test showed low serotonin, that still doesn't say why serotonin is low. Is serotonin low due to a specific nutritional deficiency? Toxcity? Emotional abuse? Something else?
Ordering an amino acid test
Amino acid tests can be run through specialty labs such as Genova diagnostics, and Doctors Data. Many natural health care practitioners such as Naturopathic Doctors will use such labs when appropriate.
 Lord, Richard S., J. Alexander. Bralley, and J. Alexander. Bralley. Laboratory Evaluations for Integrative and Functional Medicine. Duluth, GA: Metametrix Institute, 2008. 185. Print.
 Lord, Richard S., J. Alexander. Bralley, and J. Alexander. Bralley. Laboratory Evaluations for Integrative and Functional Medicine. Duluth, GA: Metametrix Institute, 2008. 198. Print.
 Lord, Richard S., J. Alexander. Bralley, and J. Alexander. Bralley. Laboratory Evaluations for Integrative and Functional Medicine. Duluth, GA: Metametrix Institute, 2008. 252. Print.
 Lord, Richard S., J. Alexander. Bralley, and J. Alexander. Bralley. Laboratory Evaluations for Integrative and Functional Medicine. Duluth, GA: Metametrix Institute, 2008. 219. Print.
 Lord, Richard S., J. Alexander. Bralley, and J. Alexander. Bralley. Laboratory Evaluations for Integrative and Functional Medicine. Duluth, GA: Metametrix Institute, 2008. 222. Print.