Organic acid test (OAT) has gained popularity among many functional health experts in recent years. A large part of the test looks at metabolites involved in energy production, including those involved in carbohydrate and fatty acid metabolism and mitochondrial markers. But how informative are these markers? Read the article and judge for yourself.
What is the Organic Acid Test?
Organic Acid Test, popularly known as OAT, measures the levels of organic compounds in urine that are produced in the body as a part of many vital biochemical pathways. It’s used to check for RARE inborn genetic defects of metabolism, most often in newborns.
A defect in a particular pathway can result in either accumulation or lowered levels of its byproducts. Thus, measuring the levels of these markers can help to identify which metabolic process is blocked or compromised.
However, OAT has been increasingly available as a pricy, direct-to-consumer test recommended by many alternative practitioners. In this article, we will break down the science behind testing for the glycolytic cycle, mitochondrial or Krebs cycle, and fatty acid metabolites. Read on to find out which ones are actually worth testing.
Carbohydrate Metabolism – Glycolytic Cycle Metabolites
Glycolysis is the first step in glucose metabolism (breakdown of sugar) producing pyruvate and some energy (ATP). This step takes place in the absence of oxygen. Pyruvate, then, enters mitochondria and is converted into acetyl CoA, which is then metabolized in the Krebs cycle to produce more energy in the presence of oxygen.
1) Pyruvic Acid (Pyruvate)
Pyruvic acid is created in the metabolism of carbs, proteins, and fats. It is one of the intermediate compounds our body uses to convert food into energy [1].
Apart from its role in energy metabolism, pyruvic acid is also an antioxidant and helps decrease inflammation [2].
When mitochondrial functions are compromised due to low oxygen supply or other factors, glycolysis becomes the major source of energy, producing more pyruvate. Excess pyruvate has an escape route where it is converted to oxaloacetate and lactic acid [3]. Thus, pyruvate levels are usually evaluated with levels of lactic acid and other organic acids.
A pyruvic acid test can tell you if there is a lack of oxygen in your body or issues with your blood vessels. A lactic acid (lactate) test, however, is more reliable and much more often used for these purposes.
These can increase pyruvate levels:
- Strenuous exercise [4, 5, 6]
- Migraines [7]
- Thiamine (vitamin B1) deficiency [8]
- Magnesium deficiency [8]
- Biotin (vitamin B7) deficiency [9]
- Circulatory failure (shock) [10]
- Heart failure [11]
- Parkinson’s [12]
- Diabetes [13]
- Cancer [14, 15]
- Rare inborn disorders — very high pyruvate levels can point to inborn metabolic disorders due to genetic mutations [16, 17, 18]
Since pyruvate levels can increase due to various causes, they are not particularly informative, unless they are used to check for rare metabolic disorders. If your levels are elevated, work with your doctor to find out why and to treat the underlying cause.
2) Lactic Acid (Lactate)
Lactic acid is produced in the body as cells convert food (glucose) into energy. It gets used and removed quite efficiently, and therefore the blood and urine levels are normally low [19, 20].
Larger amounts of lactic acid are produced by the muscles, brain, and other tissues when there is not enough oxygen. This process is known as the anaerobic (= without oxygen) metabolism of glucose. This often happens during exercise, for example. Some gut bacteria also produce lactic acid [19, 20].
Lactic acid gets broken down in the liver and kidneys and can accumulate in the body when it is produced faster than it can be removed [19, 20].
Lactic acid in excess can lower the pH of the blood and cause what is known as lactic acidosis. A lactic acid test is often ordered when a person has signs of low oxygen (hypoxia) and lactic acidosis such as [19]:
- Shortness of breath
- Rapid breathing
- Paleness
- Sweating
- Nausea
- Muscle weakness
- Abdominal pain
Higher lactic acid levels can be caused by many different factors and conditions, including:
- Strenuous exercise — when there is an imbalance between oxygen delivery and energy requirements in the muscles [21, 22, 23, 24, 25, 25]
- Asthma [26, 20]
- Thiamine (vitamin B1) deficiency, often encountered in malnutrition [27, 28, 29, 30]
- Magnesium deficiency [31]
- Gut bacterial dysbiosis, found in short bowel syndrome and after gastric bypass surgery [32, 33, 34, 35, 36, 37]
- Probiotics — in people who are susceptible [38, 39]
- Diabetes [40, 41, 42, 43]
- Inflammatory bowel disease (IBD) [40]
- Seizures [44, 45]
- Thyrotoxic crisis, caused by excessive release of thyroid hormones [46, 47, 48]
- Conditions that decrease blood flow or oxygen supply to the tissues, such as bleeding (hemorrhage) and anemia [49, 50, 51, 52, 53]
- Physical injury (trauma) and burns [20, 54, 55]
- Exposure to toxins such as cyanide (found in bitter almonds), carbon monoxide, toluene, or the pesticide fenaminosulf [56, 57, 58, 59, 60]
- Alcohol intoxication, including ingestion of ethanol, propylene glycol, ethylene glycol, and alcohol-containing products such as hand sanitizer [61, 62, 35, 63, 64]
- Many different types of medication, including metformin, beta-2 agonists, antiviral drugs, antibiotics, etc. [65, 66, 67, 68, 69, 70, 71, 72, 73]
- Drugs of abuse, such as cocaine and synthetic marijuana [74, 75]
- Malaria [76]
- Liver failure [20, 77]
- Heart failure [20]
- Cancer and cancer therapy [78, 79, 80, 81]
- Inherited metabolic disorders due to genetic mutations [82, 83, 84, 85]
Severity and symptoms of lactic acidosis can vary widely depending on which metabolic pathway is not functional and can range from severe neurological degeneration in newborns (Leigh syndrome) and early death to relatively normal life with episodes of vomiting, nausea, and generalized weakness [86].
Since there are so many different things and conditions that can cause an increase in lactic acid, some of them life-threatening, it’s very important that you don’t try to self-diagnose! Work with your doctor to find out what’s causing elevated lactic acid and to treat any underlying condition.
Following the treatment regimen your doctor prescribes will help decrease lactic acid back to normal.
Mitochondrial Markers – Krebs Cycle Metabolites
Krebs cycle (also called tricarboxylic acid or TCA cycle) is the center for energy production from carbohydrates, fats, and proteins. The cycle consists of a series of reactions, with metabolites entering at various steps from other metabolic pathways [87].
One of the primary functions of the cycle is to generate NADH & FADH, which are utilized to produce energy (in the form of ATP) in the electron transport chain (ETC). Any impairment in any step due to genetic or environmental factors can, in theory, lead to higher or lower levels of organic acids.
The Krebs cycle inputs include pyruvate, byproducts of fatty acids or from the several amino-acids (glutamate, alanine) [87].
Additionally, thyroid hormones and cortisol influence the Kreb cycle [88, 87].
3) Succinic Acid (Succinate)
Succinic acid has an important role in energy production [89].
Succinic acid, besides being Krebs cycle intermediate, can also enter the cycle through branched-chain amino acid metabolism. Succinic acid metabolism is also linked with heme synthesis, ketone bodies utilization, and the GABA shunt [90].
Levels can increase when enzymes that break down succinic acid don’t work properly. This can happen due to:
- Vitamin B2 deficiency [91, 92, 93]
- CoQ10 deficiency [94]
- Bacterial infections [95, 96]
- Exposure to toxins and heavy metals [97, 98, 99, 100]
- Diabetes [101, 89]
- Bleeding (hemorrhage)/injury [102]
- High altitude, due to low oxygen [103]
- Fibromyalgia (urine) [104]
- Cancer [105, 106]
- Down syndrome [107]
- Rare genetic disorders, such as succinate dehydrogenase deficiency [108, 109, 110]
Low levels can be due to:
- Vitamin B12 deficiency [111]
- Polycystic ovary syndrome (PCOS) [112]
- Chronic fatigue syndrome [113]
- Kidney disease [114]
- Cancer [115]
Again, with so many factors affecting succinate levels, it’s important you work with your doctor to zero in on the underlying cause.
4) α-Ketoglutaric Acid (Alpha-Ketoglutarate)
Alpha-ketoglutarate, also known as alpha-ketoglutaric acid or 2-oxoglutaric acid, is an intermediary compound of energy metabolism. It is produced when cells convert food into energy [116, 117].
It’s important for making proteins and decreasing protein breakdown in bones and muscles. It also contributes to immunity [118].
Alpha-ketoglutarate is used as a supplement to improve athletic performance, and sometimes as a drug to prevent muscle breakdown after surgery [119, 118, 120].
These can increase alpha-ketoglutarate levels:
- Alpha-ketoglutarate supplements
- Thiamine (vitamin B1) deficiency [121, 122]
- Riboflavin (vitamin B2) deficiency [123, 122]
- Niacin (vitamin B3) deficiency [122]
- Pantothenate (vitamin B5) deficiency [122]
- Lithium [124]
- Obesity [125, 126]
- Fatty liver disease [125, 126]
- Diabetes [127, 128]
- Cancer [129, 130]
- Rare genetic disorders [131, 132, 133, 134, 83, 135, 136, 137]
5) Citric Acid (Citrate)
Some of the citrate comes from our diet, but most of it comes from the bones. In fact, about 90% of the total citrate in the body is stored in the bones and gets released into the blood when needed [138].
Citric acid also gets produced as a part of the energy metabolism in mitochondria. However, mitochondrial citrate doesn’t have a large impact on blood and urine citrate levels [138].
Kidneys are responsible for removing citric acid from the blood, either by breaking it down or by filtering it into the urine. The following hormones affect the kidney clearance of citrate [138]:
- Parathyroid hormone (PTH) – decreases urine citrate
- Vitamin D – decreases urine citrate
- Calcitonin – increases urine citrate
These can increase urine citrate levels:
- Eating foods high in citric acid, or taking citric acid-containing supplements, such as potassium or magnesium citrate [139]
- Malic acid supplements [140]
- Higher blood glucose [141]
- Diabetes and diabetic nephropathy [142, 143]
These can decrease citrate levels in the urine:
- Excess sodium [138]
- Cola-flavored carbonated beverages [144]
- Exercise [145, 146]
- Low citrate blood levels, due to dietary citrate deficiency [138]
- Starving or ketosis [147, 148, 138]
- Magnesium deficiency [149]
- Low potassium (hypokalemia) [147]
- Too much acid in the body (metabolic and cellular acidosis) [138, 150, 147]
- High parathyroid hormone levels (hyperparathyroidism) [138]
- E. coli infection [151]
- Some medication, such as water pills and anti-convulsants [141, 152]
- Rare genetic disorders [153]
These increase your risk of having low citrate levels:
- A diet low in vegetable fibers [154]
- Low urine volume (dehydration) [154]
- Higher intake of non-dairy animal protein [143]
- Higher body mass index (BMI) [143]
- Gout/high uric acid levels [143]
Lower uric acid levels in the urine have been linked to kidney stones and osteoporosis [155, 156, 157, 158].
Work with your doctor to find out what’s behind abnormal levels and treat any underlying condition. Improving your diet and losing weight if overweight may also help.
6) Aconitic Acid (Aconitate)
There are two forms of aconitic acid, cis-aconitic acid and trans-aconitic acid.
Your body makes cis-aconitic acid as an intermediate compound when it converts food into energy. Trans-aconitic acid, on the other hand, is found in plants such as sugar cane [159].
Studies suggest aconitic acid levels are higher in:
- Alcoholism [160]
- Metabolic syndrome [161]
- Chronic fatigue syndrome [162]
- Autism [163]
- Cancer [164]
- Rare inborn metabolic disorders [165, 166]
- Some people taking drugs used to treat asthma (budesonide and salbutamol) [167]
Lower aconitic acid levels have been found in kidney disease [168, 169].
Proponents of OAT testing state that increased aconitic acid points to depleted glutathione, i.e. they suggest supplementing with glutathione may be beneficial. However, we couldn’t find any studies showing a link between glutathione supplementation and high aconitic acid levels.
7) Fumaric Acid (Fumarate)
Fumaric acid is an intermediate compound produced in mitochondria as cells convert food to energy.
These can increase fumaric acid levels:
- Strenuous exercise [145, 146]
- Calorie restriction [170]
- Diabetes [171]
- Kidney disease [172]
- Cancer [129]
- Down syndrome [107]
- Rare genetic diseases such as fumarase deficiency or mitochondrial disease [173, 174, 175, 165, 176]
8) Malic Acid (Malate)
Malic acid contributes to the “sour” taste in fruits and vegetables, such as apples, grapes, and rhubarb. It is also added to processed foods as an additive [177].
Our cells produce malic acid as an intermediate compound of energy metabolism [178].
This may result from excessive dietary intake, or there may be an issue with energy production in mitochondria.
Fatty Acid Metabolism
Fatty acid breakdown may serve as an important source of energy in periods of stress such as fasting, strenuous exercise, illness, especially in the heart, skeletal muscles, and liver [179, 180].
Beta-oxidation, which occurs in the mitochondria, is the main pathway through which fatty acids generate acetyl-CoA, which is the fuel that allows the mitochondria to create usable energy (ATP).
Medium- and short-chain fatty acids are transported directly into the mitochondria, but long-chain fatty acids need carnitine to get transported across the mitochondrial membrane [179, 180].
9) Suberic Acid/Sebacic Acid/Adipic Acid
Adipic acid (adipate), suberic acid (suberate) and sebacic acid are breakdown products of fatty acids [181, 182]. Levels increase when the breakdown (oxidation) of fats is impaired for any reason.
Elevated levels can be seen in:
- Supplementation with medium-chain triglycerides, found in coconut and palm oil [183]
- Excessive consumption of jello, gelatin, and custards [184, 185]
- Vitamin B2 (riboflavin) deficiency – vitamin B2 is needed for fatty acid breakdown [186]
- Diabetes [187, 188]
- Inborn errors of metabolism, such as acyl-CoA dehydrogenase deficiency [189, 190, 191, 192, 193]
- Other rare inherited disorders such as adrenoleukodystrophy and Zellweger syndrome [194, 195]
- Some people taking valproic acid (Convulex, Depakote, Epilim, Stavzor) [196, 197]
10) Ethylmalonic Acid (Ethylmalonate)
Ethylmalonic acid, also known as ethylmalonate, is a branched fatty acid. It is normally an intermediate compound of the energy metabolism, but can accumulate when there are issues with mitochondria and the fatty acid breakdown [198].
Higher levels are found in:
- Anorexia [199]
- Malaria [200, 201]
- Breast cancer [202]
- Rare genetic disorders ethylmalonic encephalopathy and short-chain acyl-CoA dehydrogenase deficiency [203, 204, 205, 206, 207, 208]
11) Methylsuccinic Acid (Methylsuccinate)
Methylsuccinic acid, or methylsuccinate, is an intermediate metabolite in the breakdown of fatty acids.
Elevated levels are found in:
- Diabetes [209]
- Jamaican vomiting sickness, caused by eating unripe ackee fruit [210]
- Rare genetic disorders, such as ethylmalonic encephalopathy, short-chain acyl-CoA dehydrogenase (SCAD) deficiency, multiple acyl-CoA dehydrogenase deficiency, isovaleric acidaemia, and glutaric aciduria type I [211, 212, 213, 208, 214, 215, 216, 217, 186, 218, 219, 220, 221, 222]
12) Ketone bodies (Acetoacetic Acid and Beta-Hydroxybutyrate)
Acetoacetic acid and beta-hydroxybutyrate (also known as BHB or 3-hydroxybutyric acid) are ketone bodies. They are produced in the liver from fatty acids to be used as an energy source by other tissues in case of glucose/carbohydrate shortage [223, 224].
They are normally found in negligible amounts in blood and urine. However, when there is not enough glucose, which can happen after prolonged exercise or fasting, or when the body can’t use glucose properly, which happens in diabetes, ketone bodies become an important energy source [225, 223, 224].
Elevated levels can be categorized as ketosis (mild to moderate increase) and ketoacidosis, a life-threatening complication of diabetes with extremely high ketone body levels [223, 224].
These increase acetoacetic acid and BHB levels:
- Endurance exercise [226, 227, 224]
- Prolonged fasting [228, 224]
- Keto diet [229, 230]
- Ketone supplements [231, 232]
- Malnutrition/Starvation [233, 224, 234]
- Sleep deprivation (less than 5h sleep per night) [235]
- Diabetes [225, 236]
- Diabetic ketoacidosis (extremely high levels) [237, 238]
- Alcoholism, in alcohol ketoacidosis (extremely high levels) [239, 240, 241, 242]
- Celiac disease [243]
- Irritable Bowel Syndrome (IBS) [244]
- Inflammatory bowel disease (IBD) [245, 246]
- Heart failure [223]
- Rare genetic disorders [247, 248]
Studies suggest that BHB levels gradually increase as we age [223].
People will check their urine ketones to make sure their blood sugar is under control in diabetes or to make sure they are in ketosis when on a ketogenic diet.
Seek immediate medical attention if your ketones are very high!
13) Gamma-Hydroxybutyric Acid
Gamma-hydroxybutyric acid (GHB), also called 4-hydroxybutyric acid, occurs naturally in the nervous system and can be found in trace amounts in the brain. It is produced from glutamate and can be converted to GABA, a major inhibitory neurotransmitter [249, 250].
GHB is also present in trace amounts in many alcoholic and non-alcoholic drinks, including tonic water and wine [251, 252].
In addition, it is used as a psychoactive drug for the treatment of sleep disorders, fibromyalgia, and alcoholism [253, 254, 255]. This compound is also notorious for being abused as a recreational and dance club drug [256, 257].
Slightly elevated levels may occur in:
Very high levels of gamma-hydroxybutyric acid indicate a genetic disorder, called succinic semialdehyde dehydrogenase deficiency (SSADHD) [260].
Takeaway
So-called mitochondrial markers are mainly used to diagnose rare genetic disorders, and there’s likely no benefit to testing them for any other reasons.
There are many other tests that doctors can use to evaluate your overall health that are reliable and backed up by plenty of studies and actual science.
Among all of the markers reviewed above, there are three tests that doctors may actually use, depending on your signs, symptoms, medical history, and other test results:
- Lactic acid – used to check for disturbances in blood pH (lactic acidosis)
- Citric acid – used in people with or at risk of kidney stones
- Ketone bodies – used to check blood sugar control in diabetes or confirm ketosis on keto diets
If your levels on any of the tests are abnormal, work with your doctor to find out why and treat any underlying health issues.
Further Reading
To find out which parts of the OAT test can be useful, and which are nonsense, we delve into the science and look into each of the marker types in isolation:
