Lactic acidosis

Lactic acidosis is a serious metabolic condition that occurs when lactic acid builds up in the bloodstream faster than the body can clear it, causing a high anion gap metabolic acidosis often first detected as an elevated lactate level on blood tests. It develops when lactate production increases, clearance by the liver or kidneys decreases, or both—disrupting the body’s normal acid–base balance.

Lactate is produced during normal energy metabolism, especially when oxygen delivery is limited or energy demand is high. In lactic acidosis, this balance is overwhelmed, leading to accumulation of acid in the blood.

Types and Mechanisms

Lactic acidosis is commonly classified in clinical practice into two main types:

Type A (hypoxic):
Caused by inadequate oxygen delivery to tissues, leading to anaerobic metabolism and excess lactate production. This is the most common form and occurs in conditions such as sepsis, shock, severe anemia, or cardiac arrest.
Type B (non-hypoxic):
Occurs without clear oxygen deficiency and is typically due to metabolic or toxic causes, including liver disease, medications (e.g., metformin), malignancy, or mitochondrial dysfunction.

This classification (type A vs type B lactic acidosis) helps guide diagnosis and management.

What Causes High Lactate?

Lactic acidosis can result from conditions that increase lactate production or impair its clearance:

Common causes:
- Sepsis and severe infections
- Shock (septic, cardiogenic, or hypovolemic)
- Reduced oxygen delivery (hypoxia)
Other causes:
- Liver failure (reduced lactate clearance)
- Medications (e.g., metformin, linezolid)
- Alcohol use
- Intense exercise or seizures
- Malignancy

In many cases, more than one factor contributes to elevated lactate levels. Metformin-associated lactic acidosis is rare in individuals with normal kidney function but can occur when kidney disease reduces drug clearance.

Key Biomarkers & Tests

Lactic acidosis is diagnosed and monitored through blood testing:

Lactate (elevated levels)
Anion gap (often elevated)
Blood pH (metabolic acidosis)
Serum bicarbonate (low levels)
Oxygenation markers (e.g., arterial blood gases)
Liver and kidney function tests

An elevated lactate level is the defining feature. Levels ≥4 mmol/L are often used as a marker of severe illness and are associated with higher risk of complications and mortality, particularly in conditions like sepsis.

A high anion gap typically reflects the accumulation of unmeasured acids. However, factors such as low albumin can reduce the calculated anion gap and may partially mask the severity of acidosis. In some cases—especially at lower lactate levels—lactate may be elevated without a clearly widened anion gap, which can make interpretation less straightforward.

Serial lactate measurements are widely used to monitor response to treatment and overall prognosis.

Symptoms of Lactic Acidosis

Symptoms of lactic acidosis vary depending on severity and underlying cause but may include:

Rapid or deep breathing
Nausea and vomiting
Abdominal discomfort
Weakness and fatigue
Confusion or altered mental status
Low blood pressure in severe cases

In critically ill patients, symptoms often overlap with the underlying condition (e.g., sepsis or shock).

Complications

If untreated, lactic acidosis can lead to:

Severe metabolic acidosis
Cardiovascular instability
Organ dysfunction (including kidney failure)
Increased risk of mortality, especially in critically ill patients

Many of these complications can be detected early through lab monitoring—rising lactate levels, worsening acidosis, and declining organ function are key warning signs.

Treatment & Management

Lactic acidosis treatment focuses on addressing the underlying cause and restoring normal metabolism:

Treat the underlying condition (e.g., antibiotics for sepsis, fluids for shock)
Restore oxygen delivery and circulation
Support organ function
Correct acid–base and electrolyte imbalances
Monitor closely with serial lactate and blood gas measurements

In severe cases, advanced supportive care such as intensive care monitoring or dialysis may be required.

With early recognition and appropriate treatment, lactate levels can normalize and outcomes improve. However, persistently elevated lactate is often a marker of ongoing disease severity, making continuous monitoring essential.