Vitamins, minerals and amino acids
Lysine
An essential amino acid from protein-rich food, needed among other things to build proteins and collagen.
Everything about this testWhat it measures
Lysine is an essential amino acid: the body cannot make it itself, so it has to come from food, mainly from meat, fish, dairy and legumes. It is needed to build proteins, including collagen, and to make carnitine. This test measures lysine in the blood.
- A snapshot of amino acids in blood or urine, which mainly reflects recent protein intake, fasting and supplements
- Sometimes a clue to too little protein in the diet or malnutrition, which can only be assessed together with other tests
- Rarely: an inborn metabolic disease affecting the breakdown, production or transport of amino acids; in the Netherlands this is usually already found through the heel prick or in childhood
High
In adults without symptoms, a raised value of an amino acid is usually caused by a protein-rich meal or a protein shake shortly before the sample collection, by supplements containing amino acids (such as BCAAs, glutamine, arginine or taurine), or by the blood not being processed quickly enough. Reduced kidney function, liver disease, poorly controlled diabetes and some medicines can also raise values. A single, slightly raised value usually has no significance and causes no symptoms. Rarely, a strongly raised value, especially together with abnormalities in related amino acids, fits an inborn metabolic disease.
Low
A low value is often caused by fasting, a low-protein meal, strenuous exercise or normal fluctuations during the day. Eating little or little protein for a long time, malnutrition, serious illness and pregnancy can lower several amino acids at once. A low value of one amino acid does not mean you need that amino acid as a supplement. Rarely, a low value fits an inborn disorder in the production of an amino acid.
Preparation
- Do the finger prick in the morning before breakfast: do not eat for 12 hours before and drink only water. After a meal with protein, amino acids are temporarily higher.
If your result is abnormal
A slightly abnormal value in someone without symptoms usually does not lead to further tests; the GP looks at diet, supplements, medicines and the circumstances of the sample collection, and has the test repeated while fasting if needed. With strongly abnormal values or an abnormal pattern together with matching symptoms, the GP consults, or refers you to, an internist (specialist in internal medicine) or pediatrician with experience in metabolic diseases.
Reliability
In the Netherlands, amino acids are mainly measured in specialized laboratories for metabolic diseases, at the request of a specialist when an inborn metabolic disease is suspected or to monitor its treatment and diet. According to the American laboratory standard (ACMG), blood plasma, preferably collected while fasting, is the recommended sample; urine is less reliable as a first test, because the kidneys take back most amino acids and medicines can interfere with the measurement. As a 'functional' profile for finding deficiencies or tailoring supplements in adults without symptoms, the test has not been validated.
Limitations
- Food, especially a protein-rich meal, and supplements shortly before the sample collection shift the values strongly; a fasting sample gives a more reliable picture.
- Blood must be centrifuged quickly and kept cool or frozen; otherwise some amino acids break down (including glutamine) or are released from blood cells. With home sample collection or shipping, this is a real risk.
- Time of day, exercise, age, pregnancy, kidney function and medicines (such as some epilepsy medicines) affect the result.
- Laboratories use different methods and reference values; results from different laboratories are hard to compare.
How common is this
Inborn disorders of amino acid metabolism are rare. In the Netherlands, the heel prick finds on average about 12 children with PKU (phenylketonuria) per year and about 1 child with MSUD (maple syrup urine disease) or tyrosinemia type 1. There are no Dutch figures on abnormal amino acid values in adults without symptoms.
Who is this useful for
In hospitals, a specialist uses this test when a metabolic disorder is specifically suspected, or to monitor a known metabolic disease and the diet that goes with it. For adults without symptoms, to find nutritional deficiencies or to choose supplements, the test is not useful according to current knowledge. If you use protein supplements or single amino acids, you get a result that mainly shows that intake.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results