The lactate test is primarily ordered to help detect and evaluate the severity of hypoxia 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 Comprehensive Metabolic Panel, Basic Metabolic Panel and Complete 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.

Venous or arterial lactate concentrations may be ordered when a patient has symptoms of hypoxia such as shortness of breath, rapid breathing, paleness, sweating, nausea, muscle weakness, abdominal pain, or coma. 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.

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.

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 localized 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 (Glucophage, 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.

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