Lactic Acidosis

What lactate is

When cells break down glucose for energy without enough oxygen, they produce lactate. Even at rest, the body makes lactate, mainly from muscle, skin, red blood cells and the gut. The liver, and to a lesser degree the kidneys, clear it and convert it back to glucose. Normally blood lactate is below about 2 mmol/L.

Lactate rises when production increases, when clearance falls, or both. Mildly raised lactate without acidosis is called hyperlactatemia. When lactate is high enough to make the blood acidic (a form of metabolic acidosis), it is called lactic acidosis.

Causes

Type A: poor oxygen delivery (most common)

• Sepsis and septic shock
• Shock from blood loss, severe dehydration, heart attack or heart failure
• Cardiac arrest
• Severe low oxygen from respiratory failure or carbon monoxide poisoning
• Severe anemia
• Loss of blood flow to part of the body, such as the bowel (mesenteric ischemia) or a limb
• Seizures and extreme exercise (usually short-lived)

Type B: without obvious low oxygen

• Liver failure: reduced clearance of lactate
• Medicines: metformin (mainly when kidney function is severely reduced or with acute illness), some HIV medicines (older nucleoside drugs), linezolid, propofol infusion, high-dose epinephrine and albuterol
• Toxins: alcohol, methanol, ethylene glycol (antifreeze), cyanide, salicylate (aspirin) overdose
• Thiamine (vitamin B1) deficiency, in heavy drinkers or malnutrition
• Cancers, especially lymphomas and leukemias
• Diabetic ketoacidosis may be accompanied by raised lactate
• Inherited metabolic and mitochondrial disorders

D-lactic acidosis

A rare type in people with short bowel syndrome or bowel bypass, when gut bacteria ferment carbohydrates into D-lactate. It causes episodes of confusion, slurred speech and unsteadiness after carbohydrate-rich meals. Standard lactate tests do not detect it.

Metformin and lactic acidosis

Metformin is a widely used, safe diabetes medicine. Metformin-associated lactic acidosis is rare. The risk rises when metformin builds up because of severely reduced kidney function, or when another illness, such as sepsis, dehydration, heart failure or liver failure, also raises lactate. The FDA advises that metformin is not used when kidney function (eGFR) is below 30, should not be started when eGFR is between 30 and 45, and should be paused during certain situations, such as before some contrast scans or during acute illness, as directed by a clinician. Do not stop metformin on your own without discussing it with your doctor.

Symptoms

• Fast, deep breathing (the body's attempt to blow off acid)
• Nausea, vomiting and belly pain
• Weakness and tiredness
• Muscle pain or cramps
• Confusion, drowsiness
• Fast heart rate and low blood pressure
• Symptoms of the underlying cause, such as fever in sepsis

Diagnosis

• Blood lactate: above 2 mmol/L is raised. Above 4 mmol/L is a marker of severe illness, especially in sepsis.
• Arterial or venous blood gas: pH and bicarbonate show acidosis.
• Electrolytes: to calculate the anion gap, which is high in lactic acidosis.
• Tests for the cause: blood cultures, kidney and liver function, blood count, toxicology screen, glucose and ketones, heart tests and imaging.

Treatment

Treatment targets the underlying cause:

• Restore circulation and oxygen: IV fluids, oxygen, medicines to support blood pressure, blood transfusion if needed.
• Treat infection: prompt antibiotics and control of the source in sepsis.
• Stop causative medicines such as metformin.
• Dialysis: for severe metformin-associated lactic acidosis, some poisonings and kidney failure.
• Thiamine for suspected deficiency.
• Antidotes for specific poisonings.
• Bicarbonate is generally reserved for very severe acidosis or specific situations, as evidence of benefit is limited.

Doctors repeat lactate measurements to see whether treatment is working: falling lactate is a good sign.

Outlook

Outcome depends on the cause and how quickly it is treated. Lactic acidosis from sepsis or shock indicates serious illness, and high or persistent lactate is linked to higher mortality. Lactic acidosis from a reversible cause, such as a seizure or medicine buildup treated with dialysis, often resolves fully.

Frequently asked questions

What are the symptoms of lactic acidosis?

Common symptoms include fast, deep breathing, nausea, vomiting, belly pain, weakness, muscle pain, confusion and drowsiness. People are often also very unwell from the underlying cause, such as sepsis, shock or liver failure. It needs emergency care.

What causes lactic acidosis?

The most common causes are conditions that reduce oxygen delivery to tissues, such as sepsis, shock, heart failure and severe bleeding. Others include liver failure, metformin buildup with kidney failure, thiamine deficiency, alcohol and toxic alcohols, some cancers and inherited metabolic disorders.

Does metformin cause lactic acidosis?

Rarely. Metformin-associated lactic acidosis mainly occurs when kidney function is severely reduced or during acute illnesses such as sepsis, dehydration or heart failure. For most people with normal kidney function, metformin is very safe. Your doctor will check kidney function regularly.

What is the difference between type A and type B lactic acidosis?

Type A is caused by poor oxygen delivery to tissues, as in shock, sepsis or cardiac arrest. Type B occurs without obvious low oxygen and is caused by problems such as liver failure, medicines like metformin, toxins, thiamine deficiency or cancer.