What is Amino Acids Blood Test? 

Amino acids are the basic building blocks of proteins - the macronutrient that makes up most of our body tissues. Our body needs 20 amino acids to function. Some of these are made inside the body (non-essential), while others are obtained from the diet (essential). 

Regardless of the source, amino acids perform various important functions in our body ranging from nitrogen storage to the formation of enzymes and neurotransmitters (signalling compounds that help transmit messages between brain cells). Fluctuations in the levels of amino acids would hence affect the overall health. 

These fluctuations may either be due to metabolic errors or genetic abnormalities that affect the body’s ability to take up the amino acids. 

An amino acids blood test measures the concentration of amino acids circulating in your bloodstream. This test is used to check if a health condition is due to a deficiency or excess of a certain amino acid. 

  1. Why is Amino Acids Blood test performed?
  2. How do you prepare for an Amino Acids Blood test?
  3. How is an Amino Acids blood test performed?
  4. What do Amino Acids Blood test results mean?

Your doctor may order this test if they observe the following signs and symptoms associated with faulty amino acids metabolism in your body: 

  • Seizures
  • Inability to thrive
  • Lethargy
  • Developmental delay
  • Movement disorders
  • Liver dysfunction in new-borns

This test may also be ordered if your present with the following symptoms or conditions:

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You may have to fast before this test. If the test is being done for a newborn, the baby should not be fed for four hours before the test. 

For assessment of a particular amino acid, your doctor may recommend a diet rich in that amino acid prior to the test. You may maintain moderate hydration before the fasting period.  

Amino acid concentration levels may be affected by various factors such as:

  • Sleeping pattern
  • Drugs such as amphetamines, norepinephrine, levodopa, almost all antibiotics, and intravenous therapy
  • Age
  • Time of sample collection 
  • Pregnancy 

So, please share your complete medical history with your doctor before the test. 

A lab technician will draw a blood sample from a vein in your arm. After the test, you may experience mild pain at the site of the injection - it will go away on its own. 

In newborns, the sample is collected through a heel prick.

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Normal results:

The reference ranges of different amino acids tested commonly in the blood are mentioned in Table 1. 

Table 1: References ranges of some important amino acids in the blood 

Amino acid Concentration in blood in micromoles/litre (µmol/L)
Children  Adults
Alanine 200-450 230-510
Arginine 44-120 13-64
Asparagine 15-40 45-130
Aspartic acid 0-26 0-6
Cystine 19-47 30-65
Glutamic acid 32-140 18-98
Glutamine 420-730 390-650
Glycine 110-240 170-330
Histidine 68-120 26-120
Isoleucine 37-140 42-100
Leucine 70-170 66-170
Lysine 120-290 150-220
Methionine 13-30 16-30
Phenylalanine 26-86 41-68
Proline 130-290 110-360
Serine 93-150 56-140
Threonine 67-150 92-240
Tyrosine 26-110 45-74
Valine 160-350 150-310

Normal values may vary slightly among different laboratories. 

Abnormal results:

Abnormal results are indicated by either a decrease or an increase in the total levels of the amino acids. 

A decrease in the blood amino acids levels may indicate: 

  • Overproduction of hormones in the cortex of the adrenal gland 
  • Huntington's chorea (brain disorder characterised by involuntary movements)
  • Phlebotomus fever (infection caused by the bite of a sand-fly)
  • Nephrotic syndrome (kidney disorder marked by excretion of protein in the urine)
  • Rheumatoid arthritis
  • Hartnup disease (characterised by skin rashes that occur due to an inability to absorb amino acids)

Elevated total amino acids in the blood may be seen in the following conditions: 

  • Seizures
  • Acidosis
  • Kidney failure
  • Encephalopathy (brain disease) 

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.


  1. Guyton AC, Hall JE. Textbook of Medical Physiology. Protein metabolism. 11th ed. 2006. Elsevier Saunders. Pp: 852-857.
  2. Fischbach FT. A Manual of Laboratory and Diagnostic Tests. 7th ed. 2003. Lippincott Williams & Wilkins Publishers. Pp: 38, 119, 174, 176, 198, 730.
  3. Benioff Children's Hospital [internet]: University of California, San Francisco; Plasma Amino Acids
  4. South Tees Hospitals. NHS Foundation trust. National Health Service, U.K. Amino Acids (CSF, Plasma & Urine)
  5. Cleveland Clinic. [Internet]. Cleveland, Ohio. Technical Update: December 2018
  6. Aliu E, Kanungo S, Arnold GL. Amino acid disorders. Ann Transl Med. 2018;6(24):471. PMID: 30740402
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