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 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 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 test 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.