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Blood Test Tracker

Lactate (Lactic Acid)

A byproduct of making energy that rises when cells are short of oxygen or the body can't clear it. Higher levels can be a sign the body is under strain.

AI-verified against cited sources. Awaiting expert reviewAlso called LacLOINC 2524-7

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What it is

Lactate (lactic acid) is made mostly in your muscles and red blood cells when they break down sugar for energy. Your liver and kidneys clear it and turn it back into sugar. A little is always in your blood. It rises for a short time with hard exercise and falls again when you rest. This test measures how much is in your blood right now.

Why it matters

Lactate can build up when cells don't get enough oxygen, when the liver can't clear it, or when certain medicines or metabolic problems get in the way. If it gets high enough, the blood can become too acidic, which is called lactic acidosis. Hospitals measure lactate in people who are very ill, such as with a severe infection, to see how the body is coping and whether treatment is working. A single lactate can't show why it is high.

If it’s high

A higher result means lactate is being made faster than the body clears it. Short-lived rises are common after hard exercise, a clenched fist during the draw, or a sample that sat too long. Higher levels can also be linked to low blood flow or oxygen, severe infection, liver or kidney disease, or certain medicines. The test can't show the cause, so your clinician reads it with your symptoms and other results.

Common causes

  • Hard exercise before the test, a clenched fist or a long tourniquet during the draw
  • A sample that sat too long before it was processed
  • Certain medicines, including metformin, aspirin, some HIV medicines, and drugs such as albuterol or epinephrine
  • Heavy alcohol use or low vitamin B1 (thiamine)
  • Severe infection, shock, heart failure, severe lung disease or severe anemia, which limit oxygen delivery
  • Liver or kidney disease, which slow the clearing of lactate
  • Uncontrolled diabetes, some cancers such as leukemia, seizures, or inherited mitochondrial disorders

What can help

  • Rest before the test, avoid hard exercise, and relax your hand during the draw
  • Ask your clinician whether a repeat sample, handled carefully, would help
  • Ask your clinician whether any medicine you take could be involved, and do not stop any medicine on your own

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

See Lactate by age and sex, with the U.S. survey numbers where they exist.

What can affect your result

  • Exercise, fist clenching and a long tourniquet raise lactate
  • Time and temperature: lactate keeps rising in the tube until the sample is chilled and the plasma is separated
  • Medicines, alcohol and vitamin B1 status
  • Sample type: plasma on a chemistry analyzer and whole blood on a blood gas machine measure the same thing. Arterial and venous values agree well when someone is well and less well in acute illness
  • Age: Mayo's upper limit is higher in infants and young children than in adults
  • Hard exercise before the draw, clenching your fist, or a long tourniquet can raise lactate. ARUP asks for fasting, complete rest, no hand or arm exercise, and a draw without a tourniquet if possible.
  • Delays raise the number. Cells in the tube keep making lactate, so ARUP asks for a gray-top (fluoride/oxalate) tube chilled in ice and plasma separated within 15 minutes. In a 2025 study, lactate was higher in 99.6% of blood gas samples left at room temperature for an hour (and then dropped and shaken).
  • Some medicines can raise lactate, including metformin, aspirin, some HIV medicines (NRTIs) and drugs such as albuterol or epinephrine. Do not stop any medicine without talking to your clinician.
  • Low vitamin B1 (thiamine) and heavy alcohol use can raise lactate.
  • This test measures L-lactate only. It does not detect D-lactate, an uncommon cause of acid build-up.

Lactate changes within minutes to hours. It rises during hard exercise and falls quickly when you rest, and in illness it follows blood flow and oxygen delivery.

When to talk to a clinician

A high lactate with symptoms such as shortness of breath, nausea and vomiting, muscle weakness, sweating or belly pain needs urgent care: call 911 or your local emergency number. If your lab flagged the result as critical, call the clinician who ordered the test today. US hospital lists most often treat about 4 mmol/L (36 mg/dL) as urgent, with lists ranging from 2 to 8 mmol/L, and ARUP's list uses 5 mmol/L (45 mg/dL).

Questions you could ask

  • Does my lactate need any follow-up, given my other health conditions?
  • Could exercise, the way the blood was drawn, or a medicine I take explain this result?
  • Should we repeat the test with a fresh, carefully handled sample?
  • Do my other results, like blood pH or bicarbonate, help explain it?

Questions people ask

How do I convert mmol/L to mg/dL?

Multiply mmol/L by 9.01, so 2.0 mmol/L is about 18 mg/dL. To go the other way, multiply mg/dL by 0.111.

Why do labs want the sample on ice?

Cells in the tube keep making lactate after the blood is drawn, so the number climbs the longer it sits. Chilling the tube and separating the plasma quickly slows that down.

Does a high lactate after a hard workout mean something is wrong?

Not necessarily. Lactate rises with hard exercise and usually falls quickly once you rest. Tell whoever draws your blood if you exercised beforehand, and talk with your clinician if you're unsure.

Show the science and sources

Units

  • 1 mmol/L = 1 mmol/L
  • 1 mmol/L = 9.009 mg/dL

Open the Lactate unit converter

Is a change real?

Lactate naturally varies about 27.2% from test to test in the same healthy person. Between two results from the same lab, a rise of 129% or more, or a fall of 56% or more, is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Desirable Biological Variation Database specifications, 2014 update (Minchinela J, Ricos C, et al.; the 'Ricos database', a compilation of median published CVI/CVG).

For clinicians and researchers

L-lactate is the end product of anaerobic glycolysis (pyruvate reduced by lactate dehydrogenase) and is cleared mainly by the liver and kidneys through the Cori cycle. Type A hyperlactatemia reflects tissue hypoxia or hypoperfusion (shock, sepsis, severe hypoxemia). Type B occurs without overt hypoxia and includes liver or kidney disease, drugs and toxins (metformin, beta-agonists such as albuterol, epinephrine, linezolid, propofol, nucleoside reverse transcriptase inhibitors, ethanol), thiamine deficiency, malignancy and inborn errors of metabolism. Sepsis-3 uses a lactate above 2 mmol/L (18 mg/dL) in the absence of hypovolemia, together with a vasopressor requirement, to identify septic shock. The 2021 Surviving Sepsis Campaign suggests measuring lactate in suspected sepsis and guiding resuscitation to lower it, and notes that cutoffs for an elevated lactate ranged from 1.6 to 2.5 mmol/L across studies. Mayo's adult upper limit of 2.0 mmol/L is footnoted as a clinical action limit. Arterial and venous lactate agree when someone is well but less in acute illness (mean venous minus arterial difference 0.34 mmol/L in 154 emergency department patients). Mayo measures plasma lactate by a colorimetric method, and some blood gas analyzers, such as the Radiometer ABL800 used in a 2025 study, use an amperometric method. The routine assay does not detect D-lactate (order D-lactate separately). Pre-analytic error is large: lactate rose in 99.6% of arterial blood gas samples held 60 minutes at room temperature and then dropped and shaken. Conversion: 1 mmol/L equals about 9.01 mg/dL.

LOINC 2524-7 (primary), 14118-4, 32693-4, 2519-7, 2518-9, 59032-3. Specimen: plasma.

Sources

  1. Lactate, Plasma (test LACS1), Mayo Clinic Laboratories (via the Mayo Clinic Laboratories Extended Catalog)
  2. Lactate, Plasma (test 3019650), ARUP Laboratories
  3. Critical Values List (CORP-APPEND-0104A, Rev. 46, April 2026), ARUP Laboratories (2026)
  4. Visualization of Critical Limits and Critical Values Facilitates Interpretation, Diagnostics (Basel) 2025;15(5):604 (survey of critical-notification lists from 50 US medical centers, 2024) (2025)
  5. Critical Decision Thresholds for Urgent Physician Notification of Point-of-Care Testing Results, Diagnostics (Basel) 2026;16(8):1139 (critical-limit lists from 417 US hospitals, 2023-2025) (2026)
  6. Lactate Test, MedlinePlus (U.S. National Library of Medicine)
  7. Lactic acidosis, MedlinePlus Medical Encyclopedia (U.S. National Library of Medicine)
  8. Type B Lactic Acidosis: Diagnosis, Etiology and Treatment - An Educational Review, Cardiology Research 2026;17:394-405 (2026)
  9. The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3), JAMA 2016;315(8):801-810 (2016)
  10. Surviving sepsis campaign: international guidelines for management of sepsis and septic shock 2021, Intensive Care Medicine 2021;47:1181-1247 (2021)
  11. Reference intervals for venous blood gas measurement in adults, Clinical Chemistry and Laboratory Medicine 2021;59(5):947-954 (2021)
  12. The Role of Venous Blood Gas Analysis in Critical Care: A Narrative Review, Medicina (Kaunas) 2025;61:1337 (2025)
  13. Comparison of peripheral venous and arterial blood gas in management of patients with respiratory complaints in the emergency department, PLoS One 2025;20:e0330190 (2025)
  14. Stability of arterial blood gas samples after delayed analysis and mechanical stress, PLoS One 2025;20:e0334710 (2025)
  15. Lactic Acid (PubChem CID 612), molecular weight 90.08 g/mol, PubChem (U.S. National Library of Medicine)
  16. LOINC codes verified with the NLM Clinical Tables LOINC search, U.S. National Library of Medicine
  17. Lactic Acid (test LACTP), University of Iowa Hospitals & Clinics, Pathology Handbook
  18. Critical Value Policy (dated 2025-07-31), Michigan Medicine Laboratories (MLabs) (2025)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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