Lactic acid (mg/dl, mmol/l)

Lactic acid, or lactate, is one of the substances produced by cells as the body turns food into energy (cell metabolism), with the highest level of production occurring in the muscles. Lactate is produced in excess by muscle cells, red blood cells, brain, and other tissues when there is insufficient oxygen at the cellular level or when the primary way of producing energy in the body's cells is disrupted.^1,2

The principal means of producing energy within cells occurs in the mitochondria, tiny power stations inside most cells of the body. The mitochondria use glucose and oxygen to produce ATP (adenosine triphosphate), the body's primary source of energy. This is called aerobic energy production. 

Whenever cellular oxygen levels decrease and/or the mitochondria are not functioning properly, the body must turn to less efficient energy production to metabolize glucose and produce ATP. This is called anaerobic energy production and the primary byproduct is lactic acid, which is processed (metabolized) by the liver.⁴

Abnormalities. Disorders or diseases caused or related ^3,4

Normally, the level of lactate in blood is low.

Lactic acid can accumulate in the body and blood when it is produced faster than the liver can break it down. Excess lactate may indicate one or a combination of the following:

Lack of oxygen (hypoxia);

The presence of a condition that causes increased lactate production;

The presence of a condition that causes decreased clearance of lactate from the body.

When lactic acid production increases significantly, the affected person is said to have hyperlactatemia, which can then progress to lactic acidosis as more lactic acid accumulates. Lactic acidosis, the most common kind of metabolic acidosis, is characterized by reduced blood pH (usually <7.25) in association with marked increase in blood lactate (usually >5.0 mmol/L). The body can often compensate for the effects of hyperlactatemia, but lactic acidosis can be severe enough to disrupt a person's acid/base (pH) balance and cause symptoms such as muscular weakness, rapid breathing, nausea, vomiting, sweating, and even coma. Some of these conditions could include:

Sepsis

Heart attack

Congestive heart failure

Severe lung disease or respiratory failure

Fluid build-up in your lungs

Very low red blood cell count (severe anemia)

Kidney disease

Diabetes that’s not under control

Leukemia

AIDS

Lactic acidosis can also occur in a person who takes metformin (Glucophage) to control diabetes when heart or kidney failure or a severe infection is also present.⁵

Deficiency of vitamin B1 (thiamine) is a very rare cause of lactic acidosis (type B) that is highlighted in two recently published papers.⁶ The mechanism of lactic acidosis in vitamin B1 deficiency is explained by the fact that thiamine is an essential co-factor for the enzyme pyruvate dehydrogenase that allows oxidation of pyruvate to acetyl CoA. But still, it is rare because thiamine deficiency is rare. A diet containing a normal amount of carbohydrates provides more than the daily requirement and in any case the body stores sufficient thiamine for a 2-3 weeks period on a diet entirely devoid of thiamine (e.g. it can occur in the context of prolonged parenteral nutrition without vitamin supplementation).

If lactate is ≥ 4.0 mmol/L, SI should be monitored

1.        Lactic Acid. University of Michigan Medicine. (October 9, 2017). Accessed on 6/5/18. Available online at https://www.uofmhealth.org/health-library/hw7871#hw7874.

2.        Lab Tests Online [Internet]. Washington D.C.; American Association for Clinical Chemistry; c2001–2019. Lactate; [updated 2018 Dec 19; cited 2019 Aug 14]; [about 2 screens]. Available from: https://labtestsonline.org/tests/lactate

3.        UF Health: University of Florida Health [Internet]. Gainesville (FL): University of Florida Health; c2019. Lactic acidosis: Overview; [updated 2019 Aug 14; cited 2019 Aug 14]; [about 2 screens]. Available from: https://ufhealth.org/lactic-acidosis

4.        Lactate Information Sheet for Clinicians. Clinical Excellence Commission. Available online at http://www.cec.health.nsw.gov.au/__data/assets/pdf_file/0007/259387/lactate-information-sheet-for-clinicians.pdf. Accessed on 6/6/18.

5.        Lactic Acidosis. Medscape. (April 27, 2018). Available online at https://emedicine.medscape.com/article/167027-overview?pa=5Z9vIFRH5l1pOUB%2Fx4oi9qbCs%2B3z8Zw4bqpC0whkiaVEcNpoHbq5x79lDN%2FYNmXz8SIvl8zjYv73GUyW5rsbWA%3D%3D. Accessed on 6/6/18.

6.        Lactate. Available on https://labtestsonline.org/tests/lactate#:~:text=Whenever%20cellular%20oxygen%20levels%20decrease,(metabolized)%20by%20the%20liver.

7.        Facts about Mitochondrial Myopathies. MDA Publications [On-line information]. (2001 November). Available online at http://www.mdausa.org/publications/mitochondrial_myopathies.html

8.        Chris Higgins. A rare cause of metabolic (lactic) acidosis highlighted. Available online https://acutecaretesting.org/en/journal-scans/a-rare-cause-of-metabolic-lactic-acidosis-highlighted