Lactic acid is a substance produced by the body, particularly in muscle and red blood cells. It is a byproduct of metabolism when cells generate energy without sufficient oxygen. While its presence is normal, extremely high concentrations in the blood signal a serious medical issue where cells are not receiving adequate oxygen. This accumulation can disrupt the body’s acid-base balance.
Normal vs. Dangerous Lactic Acid Levels
A normal resting blood lactate level is below 2 millimoles per liter (mmol/L). When levels rise, it indicates a problem with production or clearance, which is handled by the liver and kidneys. A persistent, mild to moderately high lactate level between 2 and 4 mmol/L is defined as hyperlactatemia.
The situation becomes more serious when levels exceed 4 mmol/L, a state known as severe lactic acidosis. At this threshold, the body’s pH can drop to dangerously acidic levels, interfering with organ function. Levels above 4 mmol/L are associated with a significant increase in mortality risk and require urgent medical intervention.
The Highest Documented Lactic Acid Level
One of the highest reported lactic acid levels in a patient who survived is 40.0 mmol/L. This level is more than 20 times the upper limit of the normal range and is typically considered incompatible with life. The case involved a 40-year-old woman who ingested a massive overdose of metformin, a diabetes medication known to cause lactic acidosis in cases of overdose.
The patient developed profound lactic acidosis, with her blood pH dropping to 6.59, a level of acidity that is often fatal. She became unresponsive and required intensive medical support, including hemodialysis to filter the metformin and lactate from her blood. Remarkably, she made a complete recovery without lasting neurological damage, a rare outcome for such an extreme case.
Causes of Extreme Lactic Acidosis
Extreme elevations in lactic acid are categorized into two main types. Type A lactic acidosis is the most common and results from inadequate oxygen delivery to tissues throughout the body. This can be caused by conditions that lead to systemic shock, such as severe infections (sepsis), heart attacks, major blood loss, or cardiac arrest.
Type B lactic acidosis occurs without widespread tissue hypoxia and is instead related to metabolic problems or toxins. Certain medications are a primary cause, with metformin being a well-known example. Other causes include liver failure, which impairs the body’s ability to clear lactate, alcohol use disorder, and some cancers like leukemia and lymphoma.