Also Known As
Lactic Acid
Formal Name
Lactate
This article was last reviewed on
This article waslast modified on 19 November 2018.
At a Glance
Why Get Tested?

To help detect hypoxia and other diseases that cause excess production or reduced removal of lactate from the blood

When To Get Tested?

If you have symptoms such as rapid breathing, sickness, and sweating that suggest a lack of oxygen or an acid/base imbalance; if your doctor suspects that you may have an inherited metabolic or mitochondrial disorder

Sample Required?

A blood sample taken from a vein in your arm; sometimes a blood sample collected from an artery and, rarely, a sample of cerebrospinal fluid collected from the spine

Test Preparation Needed?

Fasting may or may not be required. Ask your doctor. You may also be told not to exercise for a period of time before this test.

On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you will be able to access your results online.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, gender, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

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 (oxygen deficient) energy production and is usually present at low concentrations 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) which is the body’s main source of energy.

When cellular oxygen levels are low, or the mitochondria are not working properly, the body must turn to less efficient anaerobic energy production to metabolise glucose and produce ATP. In this process, the primary by-product is lactic acid, which can build up faster than the liver can break it down. When lactic acid levels increase a lot in the blood, the affected person is said to have first hyperlactataemia and then lactic acidosis (LA). 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, feeling sick, vomiting, sweating, and even coma.

Lactic acidosis is separated into two types: A and B. Type A is more common and 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 LA 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 lactate concentrations.

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 lumbar puncture.

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

Fasting may or may not be required. Ask your doctor. You may also be told not to exercise for a period of time before this test.

Accordion Title
Common Questions
  • How is it used?

    The lactate test is mainly requested to help detect and measure the severity of low levels of oxygen in the body (hypoxia) and also lactic acidosis. It may be used with blood gases (to look at the body’s acid/base balance and oxygenation) and/or with groups of tests, such as a metabolic screen or a full blood count, in a patient with evidence of acidosis. In patients being treated for a rapidly developing condition (such as shock or heart attack) or a slowly developing condition (such as severe congestive heart failure), lactate concentrations may be requested at intervals to help monitor hypoxia and the response to treatment.

    Lactate measurements are mainly performed on venous blood samples, but arterial blood lactate tests may also be requested, especially when the lactate test is used with arterial blood gases. A cerebrospinal fluid (CSF) lactate test may be used with a blood lactate test to help distinguish between viral and bacterial meningitis.

  • When is it requested?

    Venous or arterial lactate concentrations may be requested when a patient has symptoms of hypoxia such as shortness of breath, rapid breathing, paleness, sweating, feeling sick, muscle weakness, stomach pain, or coma. The test may be requested 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 requested with other tests to help measure the patient’s condition and then, if significantly elevated, at intervals to monitor the condition.

    In particular, this test may be used as part of an initial evaluation of someone who is suspected of having sepsis. Typically if their lactate concentration is above normal limits, treatment will be initiated without delay. If a person with sepsis can be diagnosed and treated promptly, their chances of recovery are significantly improved.

    CSF and blood lactate concentrations may be requested when a patient has symptoms of meningitis such as severe headaches, fever, delirium, and loss of consciousness.

  • 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 removal. This can be anything from an increase of lactate in muscle due to strenuous exercise up to life-threatening fully body (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 medicines, such as metformin (taken by people with diabetes) 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 concentrations suggest bacterial meningitis while normal or slightly elevated concentrations 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.

  • Is there anything else I should know?

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

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

    Generally, no. However, if your elevated lactate concentrations 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 concentration. 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. Lactate levels elevated in muscle by strenuous exercise return to normal upon resting.

  • 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 request 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 requested, the doctor may request a venous lactate because it gives him an adequate evaluation of your lactate concentrations and because the collection process is not as uncomfortable.