Paracetamol Poisoning - Diagnosis

Authored by Dr Gurvinder Rull, 09 Jul 2017

Patient is a certified member of
The Information Standard

Reviewed by:
Dr Adrian Bonsall, 09 Jul 2017

This mainly consists of blood tests and includes:

  • Paracetamol levels:
    • If the tablets were all taken in one go: the paracetamol level needs to be checked four hours after the time of the overdose. If the time is unknown or more than four hours have passed then a sample will be taken immediately.
    • If the tablets have been taken over several hours or days: this is called a 'staggered overdose' and a paracetamol level will be taken immediately and treatment started before the level is back. The level here only tells us that paracetamol has been taken.
  • Liver function tests: these are a group of blood tests that reveal how the liver is functioning. Early on, they may be normal. When they go high this tells us that liver cells have died and liver failure is possible. A blood clotting test (called prothrombin time) is an earlier and better indicator of liver damage.
  • Prothrombin time: as part of the blood clotting tests that will be requested, this gives an idea of how 'thin' the blood is. The liver makes important factors for blood clotting. When the liver becomes damaged, the prothrombin time rises. The higher the level, the more severe the liver involvement. It will be checked several times.
  • Renal function tests: these are blood tests looking at the function of the kidney. They will show if there is any kidney damage or kidney failure.
  • Blood sugar levels: low levels (called hypoglycaemia) can occur when the liver is failing. A fingertip test will need to be done hourly.
  • Arterial blood gas: this involves an arterial blood sample being taken (usually at the wrist where the pulse is taken) and reveals levels of acid in the blood. Acid levels are very tightly controlled by the body and in paracetamol overdose acid levels can rise early. These patients are probably going to be sicker and some will develop liver failure.

Other tests that are requested will depend on each individual case and the patient's course. For example, if other medications were taken then their levels may need to be checked.

Further reading and references

Health Tools

Feeling unwell?

Assess your symptoms online with our free symptom checker.

Start symptom checker