This test measures the level of lactic acid, also known as lactate, in your blood. Lactic acid is a substance made by muscle tissue and by red blood cells, which carry oxygen from your lungs to other parts of your body. Normally, the level of lactic acid in the blood is low.
Lactic acid levels rise when oxygen levels decrease.
Low oxygen levels may be caused by:
- Strenuous exercise
- Heart failure
- Severe infection
- Shock, a dangerous condition that limits blood flow to your organs and tissues
If lactic acid levels get too high, it can lead to a life-threatening condition known as lactic acidosis. A lactic acid test can help diagnose lactic acidosis before it causes serious complications.
Hypoperfusion (=a reduced amount of blood flow) is the most common cause of lactic acidosis and hyperlactacidemia may be the only marker of tissue hypoperfusion.
Suspect lactic acidosis when unexplained anion gap metabolic acidosis is encountered, especially if azotemia or ketoacidosis are not present.
Evaluate metabolic acidosis, regional or diffuse tissue hypoperfusion, hypoxia, shock, congestive heart failure, dehydration, complicated postoperative state, ketoacidosis or nonketotic acidosis in diabetes mellitus, patients with infections, inflammatory states, postictal state, certain myopathies, acute leukemia and other neoplasia, enzyme defects, glycogen storage disease (type I), thiamine deficiency, and hepatic failure.
A spontaneous form of lactic acidosis occurs. It is a prognostic index in particular clinical settings, especially in critically ill patients in shock.
A relationship to renal disease also exists. With skin rash, seizures, alopecia, ataxia, keratoconjunctivitis, and lactic acidosis in children, consider defective biotin metabolism. Phenformin, ethanol, methanol, and salicylate poisoning and ethylene glycol may cause lactic acidosis. Acetaminophen toxicity causes lactic acidosis, sometimes with hypoglycemia. Cyanide, isoniazid, and propylene glycol are among the causes of lactic acidosis. Lactic acidosis may be due to inborn errors of metabolism.
Creatinine is higher in ketoacidosis than in lactic acidosis, by interference produced by acetoacetic acid on creatinine.
The measurement of lactate levels may be indicated in the clinical setting of metabolic acidosis. Serum salicylate, ethanol level, and osmolality may be helpful. Spontaneous lactic acidosis may be fatal. High CSF lactate levels suggest the meningitis is bacterial while low values suggest a viral cause.
- Schuster HP. Prognostic value of blood lactate in critically ill patients. Resuscitation. 1984; 11(3-4):141-146 (review). PubMed 6326218
- Thoene J, Baker H, Yoshino M, et al. Biotin-responsive carboxylase deficiency associated with subnormal plasma and urinary biotin. N Engl J Med. 1981; 304(14):817-820. PubMed 6782477
- Henning RJ, Weil MH, Weiner F. Blood lactate as a prognostic indicator of survival in patients with acute myocardial infarction. Circ Shock. 1982; 9(3):307-315. PubMed 7094222
- Bailey EM, Domenico P, Cunha BA. Bacterial or viral meningitis? Measuring lactate in CSF can help you know quickly. Postgrad Med. 1990; 88(5):217-219, 223 (review). PubMed 2216980
Anderson CT Jr, Westgard JO, Schlimgen K, et al. Contribution of arterial blood lactate measurement to the care of critically ill patients. Am J Clin Pathol. 1977; 68(1):63-67. PubMed 17295
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- Hypoperfusion (=a reduced amount of blood flow) is the most common cause of lactic acidosis.
- hyperlactacidemia (=an elevated blood lactate concentration) may be the only marker of tissue hypoperfusion.
Phosphorus is sometimes significantly abnormal in lactic acidosis.
What are causes of lactic acidosis?
Causes of lactic acidosis (usually <45 mg/dL) include:
- carbohydrate infusions,
- diabetic ketosis,
Causes of lactic acidosis (>45 mg/dL) include:
- shock (in which lactic acidosis may occur early, before fall in blood pressure, decrease in urine output),
- hypoxia (including congestive failure, severe anemia, hypotension) and malignancies.
Severe lactic acidosis can develop in minutes.
Lactic acidosis can accompany dehydration.
Blood lactate concentration correlates negatively with survival in patients with acute myocardial infarction, with persistent elevation, >36 mg/dL for more than 12 hours, being associated with poor prognosis.
- At a given bicarbonate level, the average pCO2 is lower in lactic acidosis than in diabetic ketoacidosis.
- Lactic acid determination is generally indicated if anion gap is <20 and if pH is >7.25 and the pCO2 is not elevated.
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