At a glance

Also known as

Lactic acid

Why get tested?

To help detect hypoxia (oxygen deficiency) and other conditions that cause excess production or insufficient clearing of lactate from the blood

When to get tested?

The test is usually requested in emergency departments and intensive care units in patients with severe infection, sepsis, shock and other clinical situations that suggest a lack of oxygen or an acid/base imbalance. It is sometimes requested if your doctor suspects that you may have an inherited metabolic or mitochondrial disorder, or a side effect of some drugs.

Sample required?

A blood sample drawn from a vein in your arm; sometimes a blood sample collected from an artery and, rarely, a sample of cerebrospinal fluid (CSF) collected from the spine.

Test preparation needed?

Fasting may be required. Your doctor will let you know. You may also be told to rest prior to sample collection.

What is being tested?

This test measures the amount of lactate in the blood or, more rarely, in the cerebrospinal fluid. Lactate is the ionic (electrically charged) form of lactic acid. It is produced by muscle cells, red blood cells, brain and other tissues during anaerobic energy production and is usually present in low levels in the blood. Aerobic energy production is the body’s preferred process, but it requires an adequate supply of oxygen. Aerobic energy production occurs in the mitochondria, tiny power stations inside each cell of the body that use glucose and oxygen to produce ATP (adenosine triphosphate), the body’s primary source of energy.

When cellular oxygen levels are decreased, however, and/or the mitochondria are not functioning properly, the body must turn to less efficient anaerobic energy production to metabolise glucose and produce ATP. In this process, the primary byproduct is lactic acid, which can build up faster than the liver can break it down. When lactic acid levels increase significantly in the blood, the affected person is said to have first hyperlactataemia and then lactic acidosis. The body can often compensate for the effects of hyperlactataemia, but lactic acidosis can be severe enough to disrupt a person’s acid/base (pH) balance and cause symptoms such as muscular weakness, rapid breathing, nausea, vomiting, sweating and even coma.

Lactic acidosis can be separated into two types: A and B.

  • Type A may be due to inadequate oxygen uptake in the lungs and/or to decreased blood flow (hypoperfusion) resulting in decreased transport of oxygen to the tissues. The most common reason for this is shock from a variety of causes including trauma and blood loss, but lactic acidosis may also be due to conditions such as heart attack, congestive heart failure and pulmonary oedema (fluid in the lungs).
  • Type B is caused by conditions that increase the amount of lactate/lactic acid in the blood but are not related to a decreased availability of oxygen. This includes liver and kidney disease, diabetes, leukaemia, AIDS, glycogen storage diseases (such as glucose-6-phosphatase deficiency), drugs and toxins, severe infections (both systemic sepsis and meningitis), and a variety of inherited metabolic and mitochondrial diseases (forms of muscular dystrophy that affect normal ATP production). Strenuous exercise can also result in increased blood levels of lactate.
How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm. Sometimes, an arterial sample is collected by inserting a needle into an artery. Occasionally, a sample of cerebrospinal fluid is collected from the spinal column during a procedure called a spinal tap.

Is any test preparation needed to ensure the quality of the sample?

Your doctor will let you know if you need to fast. You may also be told not to exercise for a period of time before this test.

The Test

How is it used?

The lactate test is primarily ordered to help detect and evaluate the severity of hypoxia (oxygen deficiency) and lactic acidosis. It may be ordered along with blood gases (to evaluate the body’s acid/base balance and oxygenation), along with pyruvate (another ion involved in energy production), and/or along with groups of tests, such as the E/LFTs and a full blood count, in a patient with evidence of acidosis. In patients being treated for an acute condition (such as shock or heart attack) or a chronic condition (such as severe congestive heart failure), lactate levels may be ordered at intervals to help monitor hypoxia and response to treatment.

Lactate measurements are primarily taken from venous blood, but arterial blood lactate tests may also be ordered, especially when the lactate test is ordered along with arterial blood gases. A cerebrospinal fluid (CSF) lactate test may be ordered, along with a blood lactate test, to help distinguish between viral and bacterial meningitis.

When is it requested?

The test may be ordered when a patient presents with what the doctor suspects is shock, heart attack, severe congestive heart failure, renal failure, or uncontrolled diabetes. The lactate test will be initially ordered with other tests to help evaluate the patient’s condition and then, if significantly elevated, at intervals to monitor the condition. Blood lactate may be ordered when some patients on anti HIV drugs complain of symptoms like nausea, muscle weakness and abdominal pain.

CSF and blood lactate levels may be ordered when a patient has symptoms of meningitis such as severe headaches, fever, delirium and loss of consciousness. In children a raised CSF lactate might indicate congenital lactic acidosis due to inherited mitochondrial disease.

What does the test result mean?

Lactate concentrations can be increased in any condition that decreases the amount of oxygen available to the body, increases lactate production, and/or decreases lactate clearance. This can be anything from localised increases of lactate in muscle due to strenuous exercise up to life-threatening systemic shock. Excess lactate may be present in a range of diseases, infections, and inherited metabolic and mitochondrial disorders. It may also be caused by certain medications, such as metformin (taken by diabetics) and isoniazid (tuberculosis treatment).

In general, the greater the increase in lactate, the greater the severity of the condition. The presence of excess lactate is not diagnostic – it does not pinpoint the cause of the increase – but it does help the doctor to confirm or rule out possible reasons for the symptoms a patient is experiencing. For instance, when a patient has meningitis, significantly increased cerebrospinal fluid lactate levels suggest bacterial meningitis while normal or slightly elevated levels are more likely to be due to viral meningitis.

When a patient is being treated for lactic acidosis, decreasing concentrations over time reflect a response to treatment.

About Reference or “Normal” Ranges

Is there anything else I should know?

Increased lactate levels may be seen with thiamine (vitamin B1) deficiency.

Common Questions

Is there anything I can do to decrease my lactate levels?

Generally, no. However, if your elevated lactate levels are due to an underlying condition that can be addressed, such as uncontrolled diabetes or a substance that can be avoided, such as ethanol, then you may be able to lower them. If you have been diagnosed with a condition, such as a metabolic disorder, following your prescribed treatment regimen should control your lactate levels. If the increase is due to a temporary condition, such as shock or infection, then they will usually return to normal after the condition has been resolved.

Why would my doctor choose to measure arterial lactate rather than venous lactate?

Lactate measurements from arterial blood are thought to be more accurate and, because a tourniquet is not used, they are not generally affected by the collection process. Your doctor may order an arterial lactate for these reasons or because arterial blood gases are also being collected (and the same sample can be used). When other arterial blood tests are not being ordered, the doctor may order a venous lactate because it gives him an adequate evaluation of your lactate concentrations and because the collection process is not as uncomfortable.

Last Review Date: April 7, 2011