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), along with pyruvate (another ion involved in energy production), 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.
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.
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.
This article was last reviewed on 13 December 2011. | This article was last modified on 2 July 2012.
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