What is a lactate test?

This test measures the level of lactate, also called lactic acid, in a sample of your blood. In certain cases, cerebrospinal fluid (CFS) may be used. Normally, you have low levels of lactate in your blood and CFS. High levels of lactate may be a sign of a wide variety of medical conditions.

Lactate is mostly made in your muscles and red blood cells when they break down food for energy. Most of the time, your cells use oxygen to break down food for energy. But if your cells can't get enough oxygen, they can switch to another process for making energy that doesn't use oxygen. This backup process makes lactate. Your liver and kidneys turn the lactate into glucose (sugar) that your cells use for energy.

It's normal to have brief increases in lactate when you're exercising or doing other hard physical work. That's because your body uses more oxygen when you're physically active, which triggers your cells to make energy without oxygen. Usually, your lactate levels decrease quickly when you stop the activity.

But certain medical conditions can cause a harmful buildup of lactate. If lactate levels get too high, your blood becomes too acidic. This can lead to serious health problems and a life-threatening condition called lactic acidosis.

Many types of conditions can cause lactate buildup. They fall into two main groups:

• Conditions that reduce the amount of oxygen that gets to your cells. These are conditions that:
  • Affect your breathing
  • Reduce the flow of oxygen-rich blood in your body
  Examples include:
  • Shock
  • Heart failure
  • Lung diseases
  • Anemia
  • Severe infection and sepsis
• Conditions that affect how much oxygen your body uses and disorders that affect how your body makes energy or gets rid of extra lactate. Examples include:
  • Liver and kidney diseases
  • Diabetes that isn't controlled
  • Leukemia
  • Mitochondrial disorders that you inherit
  • Using certain medicines or being exposed to certain toxins (poisons)
  • Very strenuous exercise for a long time, such as running a marathon

A lactic acid test can help find high levels of lactic acid before they cause serious health problems But the test cannot diagnose the cause.

Other names: lactic acid test, lactic acid: plasma, L-lactate

What is it used for?

A lactate blood test is most often used to diagnose lactic acidosis and find out how severe it is. It can also help evaluate and monitor many types of medical conditions that may make lactate levels rise.

If a person appears to have meningitis, an infection of the brain and spinal cord, the test may be used to help find out if it is caused by bacteria or a virus. Because meningitis is an infection of the brain and spinal cord, both cerebrospinal fluid and blood may be tested.

Why do I need a lactate test?

You may need a lactate test:

• If you have symptoms of lactic acidosis, such as:
  • Shortness of breath
  • Nausea and vomiting
  • Muscle weakness
  • Sweating
  • Abdominal (belly) pain
• To find out if your cells are getting enough oxygen
• To find out why you have too much acid in your blood

You may also need this test if your health care provider thinks you have signs and symptoms of any of the many conditions that can cause lactic acidosis.

If you have been diagnosed with high levels of lactate, you may need to have repeated tests to monitor your condition.

If you have symptoms of meningitis, you may need to have your lactate levels measured in your blood and your cerebrospinal fluid. Symptoms of meningitis include:

• Severe headache
• Fever
• Stiff neck
• Sensitivity to light

What happens during a lactate test?

A health care professional will take a blood sample from a vein or an artery. Blood from an artery may provide more accurate results than blood from a vein, so your provider may recommend this type of blood test, which is called an arterial blood gas (ABG) test.

To take a blood sample from a vein, a health care professional will insert a small needle into your arm. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes. Make sure you don't clench your fist during the test, as this can temporarily raise lactate levels.

To take a blood sample from an artery, a provider will usually use an artery inside the wrist. But the sample may be taken from an artery in your arm or groin. For a newborn, the sample may be taken from the baby's heel or the umbilical cord shortly after birth.

If your blood sample is taken from your wrist, the provider will first test your blood circulation. The provider will hold your wrist and apply pressure to the arteries to cut off blood flow to your hand for several seconds. Then the provider will let go of your wrist to check how quickly blood flow returns to your hand. If your blood flow is normal, the provider will collect a blood sample.

A blood sample taken from an artery tends to be more uncomfortable than most blood tests, which use a vein. So, the provider may apply some numbing medicine to your skin first. The provider will insert a needle with a syringe into the artery to remove some blood.

When the syringe is full, the provider will bandage the puncture site. Pressure will be applied to the site for at least 5 minutes to stop the bleeding.

If meningitis is suspected, your provider may also take a sample of your cerebrospinal fluid in a procedure called a spinal tap or lumbar puncture. This is usually done in a hospital.

Will I need to do anything to prepare for the test?

Your provider will tell you how to prepare for your test. Your provider may tell you to:

• Avoid exercise for several hours before the test. That's because exercise can cause a temporary increase in lactate levels.
• Fast (not eat or drink) for 8 to 10 hours before the test.

You may need to stop taking certain medicines before this test, so tell your provider about everything you take. But don't stop taking any medicines unless your provider tells you to.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

After a blood test from an artery, you may have some bleeding, bruising, or soreness at the spot where the needle was put in. Very rarely, the needle may damage a nerve or the artery. You may be told to avoid lifting heavy objects for 24 hours after the test.

What do the results mean?

The results of a lactate test can only show whether you have abnormal levels of lactate. They can't tell what's causing the problem.

A high level of lactate in a blood sample usually means you have either hyperlactatemia or lactic acidosis:

• Hyperlactatemia means your level of lactate is staying mildly or moderately high, but the acidity of your blood (pH) is still within a normal range. If lactate continues to build up, hyperlactatemia can become lactic acidosis.
• Lactic acidosis means that your lactate level is high enough to make your blood is too acidic, and it is staying high. Lactic acidosis is more serious than hyperlactatemia and needs to be treated right away.

Treatment for high levels of lactate depends on the condition that's causing the lactate to build up in your blood. Your provider will consider your symptoms, medical history, and the results of other tests to diagnose the cause.

If you had a lactate test using cerebrospinal fluid:

• High levels of lactate mean you probably have bacterial meningitis.
• Normal or slightly high levels of lactate mean you probably have viral meningitis.

Low levels of lactate are rare and not considered to be a medical concern.

If you have questions about your results, talk with your provider.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about a lactate test?

Certain medicines may cause high lactate levels, such as:

• Metformin, a medicine for type 2 diabetes
• Aspirin
• Certain medicines to treat HIV called NRTIs

If you're concerned about how these medicines may affect your risk for lactic acidosis, talk with your provider.