Lactic Acid

A lactic acid test is a blood test that measures the level of lactic acid made in the body. Most of it is made by muscle tissue and red blood cells. When the oxygen level in the body is normal, carbohydrate breaks down into water and carbon dioxide. When the oxygen level is low, carbohydrate breaks down for energy and make lactic acid.

Lactic acid levels get higher when strenuous exercise or other conditions—such as heart failure, a severe infection (sepsis), or shock—lower the flow of blood and oxygen throughout the body. Lactic acid levels can also get higher when the liver is severely damaged or diseased, because the liver normally breaks down lactic acid.

Very high levels of lactic acid cause a serious, sometimes life-threatening condition called lactic acidosis. Lactic acidosis can also occur in a person who takes metformin (Glucophage) to control diabetes when heart or kidney failure or a severe infection is also present.

A lactic acid test is generally done on a blood sample taken from a vein in the arm but it may also be done on a sample of blood taken from an artery (arterial blood gas).

A test for lactic acid is done to:

• Check for lactic acidosis. Symptoms of lactic acidosis include rapid breathing, excessive sweating, cool and clammy skin, sweet-smelling breath, belly pain, nausea or vomiting, and coma.
• See whether the right amount of oxygen is reaching the body's tissues.
• Find the cause for a high amount of acid (low pH) in the blood.

To prepare for a lactic acid test:

• Do not eat or drink for 8 to 10 hours before the test.
• Do not exercise for several hours before the test. Do not clench your fist while having your blood drawn for a lactic acid test. These activities may change the results.

The health professional drawing blood will:

• Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein. An elastic band may not be used for a lactic acid test because a band around the arm muscle may cause a false increase in lactic acid.
• Clean the needle site with alcohol.
• Put the needle into the vein. More than one needle stick may be needed.
• Attach a tube to the needle to fill it with blood.
• Remove the band from your arm when enough blood is collected.
• Put a gauze pad or cotton ball over the needle site as the needle is removed.
• Put pressure to the site and then a bandage.

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

There is very little chance of a problem from having blood sample taken from a vein.

• You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
• In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
• Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

A lactic acid test is a blood test that measures the level of lactic acid made in the body. Most of it is made by muscle tissue and red blood cells.

Normal

Normal values may vary from lab to lab. Results are ready in 1 day.

High values

A high lactic acid value indicates lactic acidosis, which can be caused by:

• Severe loss of water from the blood (dehydration).
• Blood problems, such as severe anemia or leukemia.
• Liver disease or liver damage that prevents the liver from breaking down lactic acid in the blood.
• Conditions such as severe bleeding, shock, severe infection, heart failure, blockage of blood flow to the intestines, carbon monoxide poisoning, or pulmonary embolism that prevent adequate oxygen from reaching the body's cells.
• Extremely strenuous exercise or extreme overheating.
• Poisoning by alcohol (ethanol), wood alcohol (methanol), or antifreeze (ethylene glycol).
• Some medications, such as isoniazid for tuberculosis or metformin (Glucophage) for diabetes. Lactic acidosis is a concern for people who take Glucophage to control their diabetes, especially if they have poor kidney function.

Reasons you may not be able to have the test or why the results may not be helpful include:

• Taking large doses of the medicine epinephrine.
• Taking medicines, such as isoniazid for tuberculosis or metformin (Glucophage) for diabetes.
• Using a lot of acetaminophen (such as Tylenol) or alcohol.
• Exercising prior to this test.
• Clenching a fist while the blood sample is being drawn. Also, lactic acid levels may be higher if the tourniquet is around your arm for a long time.

• Results from a lactic acid test may be more accurate when the blood is taken from an artery (arterial blood gas) rather than from a vein. For more information, see the medical test Arterial Blood Gas.
• During aerobic exercise, the heart and lungs supply adequate amounts of oxygen to the body for energy. Anaerobic exercise uses more oxygen than the lungs and heart can supply to the body so the energy supply is less, thus causing high lactic acid levels in the blood. Usually anaerobic exercise forces a person to slow down or stop exercising because lactic acid buildup causes moderate to severe muscle aches and muscle stiffness. However, some highly trained athletes learn to tolerate short periods of high lactic acid levels. During aerobic exercise, the air you breathe contains enough oxygen to use blood sugars normally and completely for the body's energy needs, and lactic acid levels do not rise.
• Lactic acid can be measured in fluids other than blood, such as spinal fluid. Lactic acid levels in body fluids often increase when an infection is present. The amount of lactic acid in spinal fluid may be measured to determine whether a brain infection is being caused by bacteria or a virus.

Other Works Consulted

• Chernecky CC, Berger BJ, eds. (2004). Laboratory Tests and Diagnostic Procedures, 4th ed. Philadelphia: Saunders.

• Fischbach FT, Dunning MB III, eds. (2004). Manual of Laboratory and Diagnostic Tests, 7th ed. Philadelphia: Lippincott Williams and Wilkins.

• Pagana KD, Pagana TJ (2006). Mosby’s Manual of Diagnostic and Laboratory Tests, 3rd ed. St. Louis: Mosby.