When the body's oxygen levels drop during exercise or sickness, it breaks down carbohydrates for fuel. This process forms lactic acid, or lactate, which is found in the red blood cells and muscles. In emergency situations, a doctor might measure this substance with a hand-held device; however, more accurate measurements can be achieved in the laboratory with a blood sample. Drawing a blood sample for this type of test is a minor procedure that carries very few risks.
A lactic acid test may be performed for a wide variety of reasons, such as suspicion of lactic acidosis, which is typically indicated by nausea and weakness. Patients may also undergo this blood test if the doctor suspects hypoxia, or lack of oxygen in the bloodstream. Symptoms of hypoxia may include sweating, rapid breathing, and nausea. This blood test may also be useful for patients with possible renal failure, sepsis, or shock, as well as congestive heart failure, uncontrolled diabetes, or a mitochondrial disorder.
Very little preparation is required for a lactic acid test. Patients should avoid exercising for several hours beforehand, because this will increase lactic acid levels and interfere with the results of the test. Occasionally, some people may be asked to fast for a brief period of time. The patient should inform the healthcare professional if he is allergic to latex, has had previous problems with drawing blood samples, or uses any blood thinners, including aspirin.
First, the skin around the inside of the elbow will be sterilized with an antiseptic. The healthcare professional will then wrap an elastic band above the elbow in order to make the vein contain more blood. After inserting the needle, the nurse will draw blood into the syringe and remove the needle. A sterile gauze will be applied to the puncture site. Patients may feel a stinging sensation or minor pain.
After drawing the blood, the doctor will send the sample to a laboratory for the test. In general, normal results of a lactic acid test should be in the range of 4.5 to 19.8 mg/dl (milligrams/deciliter). Sometimes, different laboratories use different measurements for their tests, so patients should always discuss the results with their doctors.
If the patient's test results are outside the normal range, this means primarily that his body does not have sufficient levels of oxygen which may indicate a serious medical condition, such as lung disease, liver problems, or sepsis, which is a severe infection. Abnormal results from a lactic acid test could also simply mean that the patient was clenching his fist at the time the blood was drawn, which could increase lactic acid levels. High lactic acid levels may also indicate a vitamin B1 deficiency.