To detect high levels of lactate in the blood, which may be an indication of lack of oxygen (hypoxia) or the presence of other conditions that cause excess production or insufficient clearing of lactate from the blood; this test is not meant to be used for screening for health status.
When you have symptoms such as rapid breathing, nausea, and sweating that suggest a lack of oxygen or an abnormal blood pH (acid/base imbalance); when a healthcare practitioner suspects that you may be experiencing sepsis, shock, heart attack, severe congestive heart failure, kidney failure, or inadequately treated (uncontrolled) diabetes; when a healthcare practitioner suspects that you have inherited a rare metabolic or mitochondrial disorder; when you have symptoms of lactic acidosis such as sweet-smelling breath, belly pain, confusion or cool and clammy skin
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 spinal tap.
Blood lactate levels will usually be drawn either without the use of a tourniquet or with a tourniquet that is not released during the blood draw. Tourniquet use and release and clenching of the fist can increase lactate levels in the blood sample.
In general, no test preparation is needed. In some cases, a healthcare practitioner may request that you don't exercise for several hours before the test or refrain from eating or drinking anything other than water for 8 to 10 hours prior to the test.
Lactate is one of the substances produced by cells as the body turns food into energy (cell metabolism), with the highest level of production occurring in the muscles. Depending on pH, it is sometimes present in the form of lactic acid. However, with the neutral pH maintained by the body, most of it will be present in the blood in the form of lactate. This test measures the amount of lactate in the blood or, less commonly, in the cerebrospinal fluid (CSF).
Normally, the level of lactate in blood and CSF is low. Lactate is produced in excess by muscle cells, red blood cells, brain, and other tissues when there is insufficient oxygen at the cellular level or when the primary way of producing energy in the body's cells is disrupted. Excess lactate can lead to lactic acidosis.
The principal means of producing energy within cells occurs in the mitochondria, tiny power stations inside most cells of the body. The mitochondria use glucose and oxygen to produce ATP (adenosine triphosphate), the body's primary source of energy. This is called aerobic energy production.
Whenever cellular oxygen levels decrease and/or the mitochondria are not functioning properly, the body must turn to less efficient energy production to metabolize glucose and produce ATP. This is called anaerobic energy production and the primary byproduct is lactic acid, which is processed (metabolized) by the liver.
Lactic acid can accumulate in the body and blood when it is produced faster than the liver can break it down.
Excess lactate may indicate one or a combination of the following:
- Lack of oxygen (hypoxia)
- The presence of a condition that causes increased lactate production
- The presence of a condition that causes decreased clearance of lactate from the body
When lactic acid production increases significantly, the affected person is said to have hyperlactatemia, which can then progress to lactic acidosis as more lactic acid accumulates. The body can often compensate for the effects of hyperlactatemia, 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.
There are a number of conditions that can cause high levels of lactate. See "What does the test result mean?" in Common Questions below for more information.
How is it used?
The lactate blood test is primarily ordered to help determine if someone has lactic acidosis, a level of lactate that is high enough to disrupt a person's acid-base (pH) balance.
- Lactic acidosis is most commonly caused by an inadequate amount of oxygen in cells and tissues (hypoxia). If someone has a condition that may lead to a decreased amount of oxygen delivered to cells and tissues, such as shock or congestive heart failure, this test can be used to help detect and evaluate the severity of hypoxia and lactic acidosis. It may be ordered along with blood gases to evaluate a person's acid/base balance and oxygenation.
- As lactic acidosis may also be caused by conditions unrelated to oxygen levels, this test may be used to evaluate someone who has a disease that can lead to increased lactate levels and who has signs and symptoms of acidosis. It may be ordered along with groups of tests, such as the comprehensive metabolic panel (CMP), basic metabolic panel (BMP), or complete blood count (CBC), to determine if an underlying condition, such as liver or kidney disease, is causing lactic acidosis.
- The lactate test may also be used as part of an initial evaluation of someone who is suspected of having sepsis. Typically, if the person's lactate level 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.
- Lactate levels may be used to help monitor hypoxia and response to treatment in a person being treated for an acute condition, such as sepsis, shock or heart attack, or a chronic condition, such as severe congestive heart failure.
When is it ordered?
- Shortness of breath
- Rapid breathing
- Muscle weakness
- Abdominal pain
The test may be ordered when a person has signs and symptoms that a healthcare practitioner suspects are related to sepsis, shock, heart attack, severe congestive heart failure, kidney failure, or uncontrolled diabetes.
The lactate test may be initially ordered with other tests to help evaluate a person's condition. If lactate is significantly elevated, it may be ordered at intervals to monitor the condition.
What does the test result mean?
A high lactate level in the blood means that the disease or condition a person has 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.
However, the presence of excess lactate is not diagnostic. A healthcare practitioner must consider a person's medical history, physical examination, and the results of other diagnostic tests in order to determine the cause and to diagnose the underlying condition or disease.
A number of conditions can cause elevated lactate levels. They are separated into two groups according to the mechanism by which they cause lactic acidosis.
Type A lactic acidosis, the most common type, may be due to conditions that cause a person to be unable to breathe in enough oxygen (inadequate oxygen uptake in the lungs) and/or cause reduced blood flow, resulting in decreased transport of oxygen to the tissues (decreased tissue perfusion). Examples of type A conditions include:
- Shock from trauma or extreme blood loss (hypovolemia)
- Heart attack
- Congestive heart failure
- Severe lung disease or respiratory failure
- Fluid accumulation in the lungs (pulmonary edema)
- Very low level of red blood cells and/or low hemoglobin (severe anemia)
Type B lactic acidosis is not related to delivery of oxygen but reflects excess demand for oxygen or metabolic problems. Examples of type B causes include:
- Liver disease
- Kidney disease
- Inadequately treated (uncontrolled) diabetes
- Rare glycogen storage diseases (such as glucose-6-phosphatase deficiency)
- Use of certain drugs such as aspirin (salicylates) and metformin
- Exposure to toxins such as cyanide and methanol
- A variety of rare inherited metabolic and mitochondrial diseases that are forms of muscular dystrophy and affect normal ATP production (see the Related Content below for links to more information on these)
- Strenuous exercise, as with marathon runners
When someone is being treated for lactic acidosis or hypoxia, decreasing concentrations of lactate over time reflect a response to treatment.
When someone has signs and symptoms of 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.
The lactate test measures the level of lactate in the blood at a given point in time. A normal lactate level indicates that a person does not have lactic acidosis, that there is sufficient oxygen at the cellular level, and/or that their signs and symptoms are not caused by lactic acidosis.
Is there anything else I should know?
Increased lactate levels may be seen with thiamine (vitamin B1) deficiency. Certain medications, including metformin and HIV drugs, can cause high lactate levels.
Is there anything I can do to decrease my lactate level?
Generally, no. However, if your elevated lactate level is 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 it. If you have been diagnosed with a condition, such as a metabolic disorder, following your prescribed treatment regimen should control your lactate level. If the increase is due to a temporary condition, such as shock or infection, then it will usually return to normal after the condition has been resolved.
Why would a healthcare practitioner choose to measure lactate in a blood sample from an artery rather than blood from a vein?
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. A healthcare practitioner may order an arterial lactate for these reasons or because a sample for a group of other tests called arterial blood gases (ABGs) is being collected at the same time and the same sample can be used for all tests. When other arterial blood tests are not being ordered, a healthcare practitioner may order a venous lactate because it provides an adequate evaluation of a person's lactate level and because the collection process is not as uncomfortable.
Are there other ways to measure lactate than by sending a blood sample to the lab for testing?
Yes. Lactate may be measured using a small hand-held device much like a glucose meter at the point of care (POC, at a patient's bedside) instead of in a laboratory. This type of monitoring is useful, for example, in emergency departments and intensive care units where rapid results are vital to the care of critically ill people. However, since the methods of measurement are different, the results from lactate POC tests may not be comparable with those from tests performed in a laboratory.
What is the lactate/pyruvate ratio and how is it used?
A lactate/pyruvate ratio is a calculated result that may be used to differentiate between causes of lactic acidosis.
Pyruvate is a substance produced by and used by cells in the production of energy. The mitochondria within cells metabolize glucose in a series of steps to produce ATP, the body's energy source. One of the steps involves pyruvate and the following step requires oxygen. When the oxygen level is low, pyruvate accumulates and is converted to lactate, resulting in an accumulation of lactate and lactic acidosis. An alternative cause is when there is impaired mitochondrial function and the pathway is interrupted, resulting in increased pyruvate and hence more lactate. The lactate/pyruvate ratio will be high in these cases.
However, there are certain congenital disorders (inborn errors of metabolism) in which pyruvate is not converted to lactate. One example is pyruvate dehydrogenase deficiency. In these cases, pyruvate will accumulate, the blood level will be high, and the lactate to pyruvate ratio will be low.