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Lactate Test
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Lab Tests

Lactate Test

A lactate test measures lactic acid levels in your blood or cerebrospinal fluid to help diagnose conditions that prevent cells from receiving enough oxygen.

What is a lactate test?

Lactate (lactic acid) is produced by muscles and red blood cells when they break down food for energy. While cells typically use oxygen for this process, they switch to a backup process that produces lactate when oxygen is limited. High levels of lactate can lead to lactic acidosis, a life-threatening condition where the blood becomes too acidic.

Causes of lactate buildup include conditions that reduce oxygen flow (e.g., heart failure, sepsis, lung disease) or disorders affecting how the body processes energy (e.g., liver/kidney disease, uncontrolled diabetes, mitochondrial disorders). Other names: Lactic acid test, lactic acid: plasma, L-lactate.

What is it used for?

The test is used to diagnose lactic acidosis and monitor conditions that cause lactate levels to rise. It may also be used to determine if meningitis is caused by bacteria or a virus by testing cerebrospinal fluid (CSF).

Why do I need a lactate test?

You may need this test if you have symptoms of lactic acidosis, such as shortness of breath, nausea, muscle weakness, sweating, or abdominal pain. If meningitis is suspected, symptoms include severe headache, fever, stiff neck, and light sensitivity.

What happens during a lactate test?

Blood is typically drawn from a vein or an artery. An arterial blood gas (ABG) test, which draws blood from an artery (usually in the wrist), may provide more accurate results. If meningitis is suspected, a spinal tap (lumbar puncture) may be performed to collect CSF.

Will I need to do anything to prepare for the test?

Your provider may instruct you to:

  • Avoid exercise for several hours before the test.
  • Fast for 8 to 10 hours.
  • Review your medications, as some may need to be temporarily stopped.

Are there any risks to the test?

Blood tests carry minimal risk, such as slight pain or bruising. Arterial draws may cause more discomfort, and you may be advised to avoid heavy lifting for 24 hours afterward.

What do the results mean?

  • Hyperlactatemia: Mildly or moderately high levels where blood pH remains normal.
  • Lactic acidosis: High levels that make the blood too acidic; this requires immediate treatment.
  • Cerebrospinal fluid results: High levels often indicate bacterial meningitis, while normal or slightly high levels suggest viral meningitis.

Is there anything else I need to know?

Certain medications, including metformin, aspirin, and some HIV treatments (NRTIs), can cause high lactate levels. Discuss any concerns about your medications with your provider.

Frequently Asked Questions

rterial blood provides a more accurate reflection of the body's immediate oxygen delivery and tissue perfusion status. Venous lactate levels can be influenced by local muscle activity and may lag behind actual systemic changes. In critical care settings, such as sepsis or shock, arterial sampling allows for rapid, precise monitoring of lactate clearance, which is a key indicator of how well the body is responding to treatment.
normal lactate level does not rule out sepsis or other serious infections. Lactate is a marker of tissue hypoperfusion (inadequate blood flow), which may not occur in the early stages of infection. Some patients with sepsis maintain normal lactate levels initially but may develop elevated levels later as the condition progresses. Clinicians use lactate in conjunction with other markers, such as white blood cell count, fever, and blood cultures, to make a comprehensive diagnosis.
Yes, strenuous exercise can significantly raise lactate levels because muscles switch to anaerobic metabolism when oxygen demand exceeds supply. If you are scheduled for a lactate test, your provider may ask you to rest for 15 to 30 minutes beforehand to allow levels to return to baseline. However, in emergency situations where the test is used to diagnose shock or sepsis, the immediate clinical context usually outweighs the impact of recent activity, and the trend over time is more important than a single value.
In a hospital setting, lactate levels are often monitored every 2 to 4 hours initially to assess the effectiveness of resuscitation efforts. The goal is to see a downward trend, as decreasing lactate levels indicate that tissue perfusion is improving. Once levels stabilize and the underlying cause is controlled, the frequency of testing may decrease to daily or as clinically indicated, depending on your overall health status and response to treatment.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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