Lactate (lactic acid) test
Quick answer: A lactate test measures lactic acid, which builds up when the body's tissues are not getting enough oxygen or when the body cannot clear it. It is used in serious illness such as sepsis or shock, and a spinal fluid (CSF) lactate can help doctors assess meningitis.
- SampleBlood or CSF
- TakesA few minutes for blood; about 30 minutes for a lumbar puncture
- Before the testNo special preparation is usually needed; a CSF sample is collected by a doctor through a lumbar puncture.
How the test is done
- 1For blood, a sample is taken from a vein, often in hospital while you are being treated
- 2Staff may avoid a tight tourniquet, as it can affect the level
- 3For CSF, a doctor collects fluid from your lower back during a lumbar puncture
- 4The sample is sent to the lab quickly, often on ice
What your results can mean
Reading your report
Normal ranges differ between labs, so compare your result with the range printed on your report and discuss it with your doctor.
If the result is outside the usual range
A high level can be seen with sepsis, shock, severe dehydration, heavy exercise, some medicines such as metformin in certain situations, or rare metabolic conditions. A raised CSF lactate can be seen with bacterial meningitis.
Who usually has this test
People who are seriously unwell in hospital, such as with suspected sepsis or shock, and patients being assessed for meningitis.
Risks and aftercare
A blood sample may leave a small bruise; after a lumbar puncture you may need to lie down for a while and some people get a headache.
Names and options
Also called: lactic acid test, serum lactate, CSF lactate
Options
- Plasma (blood)
- CSF (spinal fluid)
Listed by the hospital as
- LACTATE, CSF
- LACTATE, HEPARIN PLASMA
Questions about this test
What does a high lactate level mean?
A high lactate can mean your tissues are not getting enough oxygen, such as in sepsis or shock, or that the body is not clearing lactate well. It can also rise briefly after hard exercise. Doctors read it with your condition and often repeat it to see if treatment is working.
Why is lactate checked in sepsis?
In sepsis, a raised lactate can be a sign that the infection is affecting blood flow to organs. It helps doctors judge how unwell someone is and how they are responding to fluids and antibiotics.
Why is CSF lactate tested in meningitis?
Lactate in spinal fluid tends to be higher in bacterial meningitis than in viral meningitis. It is one of several CSF results, along with protein, sugar and cell counts, that help doctors decide on the cause.
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This page explains each test in general terms so you know what to expect. It is not medical advice: your doctor decides which tests you need and what your results mean. Reference ranges differ between laboratories. Updated 4 November 2026.