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This article waslast modified on 8 March 2023.
At a Glance
Why Get Tested?

In order to assess risk of liver damage after overdose and to decide on the need for protective antidote treatment. The antidote (N-acetyl cysteine) needs to be given within eight hours of the overdose to be most effective. After eight hours, efficacy decreases sharply, but the antidote should still be given up to 15 hours after the overdose.

When To Get Tested?

At least 4 hours after a single overdose, or immediately if more than one overdose has been taken within the last 1 or 2 days

Sample Required?

A blood sample taken from a vein usually in an arm

Test Preparation Needed?

No test preparation is needed

On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you may be able to access your results online. Your GP practice will be able to provide specific details.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, sex, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

What is being tested?

The plasma or serum paracetamol concentration is being measured.

Accordion Title
Common Questions
  • How is it used?

    The plasma or serum paracetamol concentration is used to establish a diagnosis of paracetamol overdose and to help decide on the need for treatment. Prompt diagnosis and treatment are important to ensure the best outcome. Patients usually have no symptoms or non-specific symptoms during the first 24 hours so testing is vital to make the diagnosis.

  • When is it requested?

    When paracetamol overdosage is a possibility, either because the patient is known to have taken paracetamol or in the case of an unknown drug overdose. The test must be performed at least four hours after suspected ingestion of the drug to allow accurate measurements to be made of the amount of drug that has been absorbed into the body.

  • What does the test result mean?

    The plasma or serum paracetamol concentration at a known time point between 4 and 15 hours after a single overdose has been taken indicates the likelihood of liver damage developing after 2 or 3 days. This test therefore helps the doctor decide on the need for antidote treatment to reduce the risk of liver damage. If treatment is not given, toxicity can develop and result in jaundice, liver and kidney failure, convulsions, coma and death. However, if prompt treatment is given there is a very good chance of full recovery.

  • Is there anything else I should know?

    Taking as few as ten 500 milligram paracetamol tablets at once can cause serious, possibly fatal liver, damage presenting 2-4 days after the overdose unless antidote treatment is given within 15 hours. It is likely that there will be no symptoms of poisoning for 24-36 hours after taking the paracetamol even if a potentially fatal dose has been ingested. If any amount of paracetamol above the recommended dose has been taken, medical help should be sought as soon as possible.

    Many prescription and non-prescription medications contain paracetamol in combination with other drugs. Read the label carefully, and never take more than one preparation containing paracetamol at a time.

  • Is paracetamol dangerous if used appropriately?

    Paracetamol is a very safe and effective drug if used at the recommended dose (in adults 2 x 500 milligram tablets or capsules taken every 4-6 hours if necessary). It is extremely unlikely that poisoning will occur if this recommended dose and dose interval is followed.

  • Is paracetamol overdose dangerous in children?

    It is unlikely that liver damage will follow after accidental ingestion of small doses of paracetamol by a child aged less than 10 years. Serious paracetamol poisoning in children is only likely if the recommended dosage is repeatedly exceeded or if a large overdose is taken.

  • Can paracetamol poisoning be treated at home?

    No. If paracetamol poisoning is suspected, the plasma paracetamol concentration must be measured in hospital as soon as possible and treatment decided accordingly.