Lactate Blood Test: Levels, Causes & Interpretation

What Is a Lactate (Lactic Acid) Blood Test?

Lactate, also called lactic acid, is a substance your body produces when it breaks down carbohydrates for energy without enough oxygen. This process, known as anaerobic metabolism, happens naturally during intense exercise. But when lactate builds up excessively in the blood, it can signal underlying problems with oxygen delivery or organ function.

In my clinical practice, I often see lactate measured in emergency settings to quickly assess how well tissues are perfused. It’s a cornerstone marker for sepsis, shock, and critical illness. The test is also used to monitor patients with exercise intolerance or inborn errors of metabolism.

Why Is Lactate Tested?

When Your Doctor Orders a Lactate Test

Doctors check lactate levels for several reasons:

• Sepsis or infection: Rising lactate can indicate that tissues aren’t getting enough oxygen due to severe infection.
• Heart failure or shock: Poor circulation starves organs of oxygen, raising lactate.
• Severe trauma or burns: Tissue damage triggers anaerobic metabolism.
• Metabolic disorders: Children with unexplained acidosis or muscle weakness may have a genetic defect affecting lactate metabolism.
• Lactic acidosis from medications: Some drugs like metformin or antiretrovirals can cause lactic acidosis in susceptible patients.
• Post-exercise monitoring: Athletes use lactate tests to gauge training intensity.

Normal Lactate Reference Ranges (by Age Group)

Reference ranges can vary between laboratories. The following table shows commonly accepted values for venous blood lactate. Arterial levels are slightly lower.

Units: mmol/L. To convert to mg/dL, multiply by 9.0. Arterial lactate is typically 0.5–1.6 mmol/L.

What Do High Lactate Levels Mean?

Is High Lactate Dangerous?

Yes, persistently high lactate (≥4 mmol/L) is a medical emergency. It indicates that the body’s tissues are starved of oxygen — a condition called lactic acidosis. My patients with high lactate often report rapid breathing, confusion, weakness, or cold, clammy skin. The most common causes in hospitalised patients are:

• Sepsis: The leading cause. Even a slight rise (2–3 mmol/L) in a sick patient warrants immediate attention.
• Cardiogenic shock: Heart failure reduces oxygen delivery.
• Haemorrhagic shock: Blood loss leads to poor perfusion.
• Severe dehydration or burns: Reduced blood volume.
• Exercise-induced: Normal after intense workout — levels return to baseline within 1 hour.
• Medications: Metformin in kidney failure, linezolid, or HIV drugs.
• Liver disease: Impaired clearance of lactate.

What Level of Lactate Requires Immediate Care?

A lactate above 4 mmol/L is considered severe and often correlates with higher mortality. However, any rise above the normal range in a symptomatic patient requires urgent evaluation. In my practice, I use the lactate clearance — the drop in level over 6 hours — to gauge response to treatment.

What Do Low Lactate Levels Mean?

Low lactate is rarely a concern. In fact, it’s often a sign that the body is well-oxygenated. However, extremely low levels (<0.2 mmol/L) can occur in:

• Glycogen storage diseases (e.g., von Gierke’s disease): The body cannot produce lactate properly.
• Severe liver failure: In late stages, lactate production fails.
• Certain medications: Bicarbonate therapy can lower measured lactate.

In most cases, low lactate is simply a good sign. Don’t worry about a mildly low result unless your doctor flags it.

Lactate During Pregnancy

Pregnancy slightly alters metabolism. Normal lactate levels in pregnancy are similar to non‑pregnant adults (0.5–2.2 mmol/L). However, because the uterus and placenta demand more oxygen, any infection or pre‑eclampsia can cause a rapid rise. In my practice, I recommend a lactate check in pregnant women with signs of infection, high blood pressure, or reduced fetal movements.

How to Prepare for a Lactate Blood Test

The test is usually done from a vein in your arm, or sometimes from an artery (for arterial blood gas).

• Fasting: You may need to fast for 8–12 hours, as food can temporarily raise lactate.
• Rest: Avoid strenuous exercise for 24 hours before the test.
• No tourniquet for too long: Prolonged fist clenching can falsely elevate lactate.
• Tell your doctor about medications: Especially metformin, acetaminophen, or alcohol use.

After the draw, you can resume normal activities. The risk of bruising or infection is minimal.

Lactate vs. Lactic Acid: What’s the Difference?

In clinical practice, the terms are used interchangeably. Strictly speaking, lactate is the ionised form of lactic acid. The body produces lactic acid that quickly dissociates into lactate and hydrogen ions. Most blood tests measure lactate, not lactic acid. So when you see “lactic acid” on your report, it’s actually the lactate level. Both names refer to the same parameter (LOINC code 32623-1).

Other Names for This Test

• Blood lactate
• Serum lactate
• Lactic acid (Lactate)
• Plasma lactate
• Arterial lactate
• Venous lactate

Frequently Asked Questions