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, that is energy production by breaking down foods without using any oxygen in the process. Lactate is usually present in low levels in the blood. Aerobic energy production is the body’s preferred process, that is production of energy by combining foods with oxygen 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 or the mitochondria are not functioning properly such as in some rare inherited disorders, the body must turn to less efficient anaerobic energy production to metabolise glucose and produce ATP. In this process, the primary by-product is lactate can build up faster than the liver can break it down. When lactate increases significantly in the blood, the patient is said to have hyperlactataemia which can then progress to become lactic acidosis as more lactic acid accumulates. 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 is classified in two groups - types A and B.

• Type A lactic acidosis, the most common type, may be due to conditions that cause someone to be unable to breathe in enough oxygen (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. However, lactic acidosis may also be due to conditions such as heart attack, congestive heart failure and pulmonary oedema (fluid in the lungs).
• Type B lactic acidosis is not related to delivery of oxygen but reflects excess demand for oxygen or metabolic problems. This includes liver and kidney disease, uncontrolled 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 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 where there is evidence of acidosis, together with groups of tests such as the E/LFTs and a full blood count. In someone being treated for an acute condition (such as shock or heart attack) or a chronic condition (such as severe congestive heart failure) regular measurement of lactate levels can help monitor hypoxia and response to treatment.

Lactate levels are usually measured in venous blood but arterial blood lactate tests may also be ordered, especially when the lactate test is ordered along with arterial blood gases so that a second specimen does not have to be collected. A cerebrospinal fluid (CSF) lactate test may be used, along with a blood lactate test, to help distinguish between viral and bacterial meningitis because CSF lactate is high in bacterial infections and lower in viral infections.

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 ordered when someone presents with what is suspected to be 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 their condition and if significantly elevated, at intervals to monitor the progress of the condition. Blood lactate may be ordered when someone on anti HIV drugs complains of symptoms such as nausea, muscle weakness and abdominal pain.

Lactate measurement 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 levels can 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 result mean?

Lactate concentrations can be increased by a range of conditions – anything from localised increases of lactate in muscle due to strenuous exercise up to life-threatening systemic shock - in other words, by any condition that decreases the amount of oxygen available to the body, increases lactate production, and/or decreases lactate clearance. 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 people with diabetes) and isoniazid (tuberculosis treatment).

A high lactate level in the blood means that the disease or condition is causing lactate to accumulate. In general, a greater increase in lactate means a greater severity of the condition. When associated with lack of oxygen, an increase in lactate can indicate that organs are not functioning properly.

The presence of excess lactate is not diagnostic – it does not pinpoint the cause of the increase – but it does help to confirm or rule out possible reasons for the symptoms someone is experiencing. For instance, when someone 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 because bacteria release more lactate as they grow.

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

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, you may be able to lower it. If you have been diagnosed with a condition, such as a metabolic disorder, your prescribed treatment regimen should control your lactate levels. If the increase is due to a temporary condition such as shock or infection, 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 or her an adequate evaluation of your lactate concentrations and because the collection process is not as uncomfortable.

More information

RCPA Manual: Lactate