Lactic acidosis is a dangerous buildup of lactic acid in the bloodstream that makes the blood too acidic. It’s diagnosed when blood lactate rises above 4 mmol/L and blood pH drops below 7.35. Unlike the temporary lactate spike you get from hard exercise, lactic acidosis signals that something has gone seriously wrong with how your body produces or clears lactic acid, and it requires emergency medical treatment.
How Lactic Acid Builds Up
Your cells normally burn glucose using oxygen to produce energy. When oxygen is scarce, or when something disrupts the normal energy-production machinery inside your cells, they switch to a backup system that doesn’t need oxygen. This backup process generates lactate as a byproduct. In small amounts, your body handles lactate easily. The liver clears most of it, converting it back into usable fuel. But when lactate is produced faster than the liver can process it, or when the liver itself isn’t working well, levels climb and the blood becomes acidic.
Both types of lactic acidosis share the same core problem: the energy-producing structures inside cells (mitochondria) can’t keep up with demand. The difference is why they can’t keep up.
Type A: Not Enough Oxygen
Type A is the more common form. It happens when tissues don’t receive enough oxygen, forcing cells into that backup energy mode on a large scale. The classic triggers are conditions that reduce blood flow throughout the body: septic shock, severe blood loss, heart failure, or cardiac arrest. Regional blockages, like a blood clot cutting off circulation to the intestines or a limb, can also drive lactate levels up.
In sepsis, lactate levels serve as a direct marker of how sick someone is. Patients admitted with initial lactate above 2.5 mmol/L have a 28-day mortality rate roughly three times higher than those below that threshold. That’s why current international guidelines from the Surviving Sepsis Campaign recommend serial lactate measurements to guide treatment in sepsis and septic shock, with fluid administration individualized based on how quickly lactate levels drop rather than simply pushing fluids until levels normalize.
Type B: No Oxygen Shortage
Type B lactic acidosis is trickier. Oxygen delivery is fine, but something else interferes with the cell’s ability to use it properly. The list of potential causes is long:
- Medications: Metformin (used for type 2 diabetes) is the most well-known culprit. Metformin-associated lactic acidosis occurs in roughly 1 to 9 cases per 100,000 people. The risk rises sharply when the kidneys aren’t clearing the drug properly, since most metformin leaves the body through urine. Kidney injury, liver failure, heart failure, or critical illness can all cause the drug to accumulate to toxic levels.
- Alcohol and toxic substances: Heavy alcohol use, methanol poisoning, and ethylene glycol ingestion can all trigger it.
- Cancer: Certain malignancies, particularly leukemia, lymphoma, and some solid tumors, can produce enough lactate to overwhelm the body’s clearing capacity.
- Nutrient deficiencies: Thiamine (vitamin B1) deficiency disrupts the normal oxygen-dependent energy pathway, shunting more glucose into lactate production.
- Liver disease: Since the liver is the primary organ responsible for clearing lactate, liver dysfunction significantly impairs the body’s ability to normalize lactate levels. Research in sepsis patients shows that those with liver disease have measurably slower lactate clearance, making recovery harder.
- Other triggers: Cyanide poisoning, HIV infection, severe trauma, and several other medications can also cause Type B lactic acidosis.
What It Feels Like
The symptoms of lactic acidosis often blend with whatever underlying condition is causing it, which makes it hard to identify on its own. Early signs tend to be nonspecific: nausea, vomiting, abdominal pain, and a general sense of feeling very unwell. Muscle weakness and fatigue are common.
As acidosis worsens, the body tries to compensate by breathing faster and deeper to blow off carbon dioxide and reduce acidity. In severe cases, this becomes a distinctive pattern of deep, labored breathing called Kussmaul breathing. Neurological symptoms can develop too, including confusion, disorientation, and in extreme cases, seizures. The heart may beat rapidly, and blood pressure can drop. These later signs indicate a medical emergency.
How It’s Diagnosed
Lactic acidosis is confirmed through blood tests. Two numbers matter most: a lactate level above 4 mmol/L and a blood pH below 7.35 (normal blood pH sits between 7.35 and 7.45). Doctors typically check lactate levels whenever someone presents with signs of shock, sepsis, unexplained rapid breathing, or other conditions where poor oxygen delivery or metabolic disruption is suspected.
For context, a healthy person at rest has blood lactate well under 2 mmol/L. Even after all-out exercise, trained athletes peak around 14 mmol/L at about six minutes post-exercise, then clear it steadily at a rate of roughly 0.3 mmol/L per minute, dropping to about half the peak value within 30 minutes. The body’s ability to self-correct after exercise is what separates a normal lactate spike from true lactic acidosis, where the clearing mechanisms are overwhelmed or broken.
How It’s Treated
The most important principle of treatment is straightforward: fix whatever is causing it. There is no effective standalone treatment for lactic acidosis itself. Restoring oxygen delivery, treating the infection, stopping the offending medication, or addressing the underlying organ failure is what brings lactate levels down.
For Type A, that means aggressive treatment of the shock state. If sepsis is the trigger, antibiotics and carefully titrated intravenous fluids are central. If the heart isn’t pumping effectively, supporting cardiac function takes priority. If a blood clot is blocking circulation, restoring flow to the affected tissue is the goal.
For Type B, the approach depends on the cause. If metformin is responsible, stopping the drug and supporting kidney function are key. In cases of toxic alcohol ingestion, specific antidotes and sometimes dialysis are used to clear the poison.
One treatment you might expect to work, giving sodium bicarbonate to directly neutralize the acid, has consistently failed to show benefit. Multiple clinical trials have found no improvement in survival or heart function from bicarbonate infusion in lactic acidosis. One retrospective study actually found an association between bicarbonate use and higher mortality. The Surviving Sepsis Campaign guidelines recommend against using it in patients with lactic acidosis whose pH is at or above 7.15. The reasoning is that acidosis is a symptom, not the disease, and buffering the acid without fixing the source doesn’t help.
Why the Liver Matters
The liver is the body’s main lactate processing center. When it’s functioning normally, it converts lactate back into glucose or burns it for energy, keeping blood levels in check. People with chronic liver disease start at a disadvantage: their baseline ability to clear lactate is already reduced. If they then develop an infection, go into shock, or experience another insult that increases lactate production, they can tip into acidosis faster and have a much harder time recovering. Research in sepsis patients confirms that liver dysfunction is significantly associated with impaired lactate clearance during early treatment, creating a population where prolonged high lactate levels are especially difficult to resolve.