People who overdose on paracetamol could be helped by a blood test that shows immediately if they are going to suffer liver damage.
Researchers in Edinburgh and Liverpool said the test would help doctors identify which patients arriving in hospital need more intensive treatment.
The blood test detects levels of specific molecules in blood associated with liver damage.
Previous studies have shown that levels of these markers are elevated in patients with liver damage long before current tests can detect a problem.
A team led by the Universities of Edinburgh and Liverpool measured levels of the three markers in more than 1,000 patients across the UK who needed hospital treatment for paracetamol overdose.
They found the test could accurately predict which patients are going to develop liver problems, and who may need to be treated for longer before they are discharged.
The test could also help identify patients who could be safely discharged after treatment, freeing up hospital beds.
About 50,000 people are admitted to hospital each year in the UK due to paracetamol overdose.
Many people unknowingly consume too much by taking paracetamol at the same time as cold and flu medications that also contain the drug.
Liver injuries are a common complication of drug overdoses. In some cases the damage can be so severe the patient needs a transplant and, in rare instances, can be fatal.
Patients with a life-threatening level of paracetamol in their blood can be treated with an antidote called acetylcysteine, given by intravenous drip.
The treatment is associated with side effects so doctors do not treat patients longer than necessary.
The researchers said the test could help to pinpoint patients who are unlikely to benefit from treatment.
The study, published in the Lancet Gastroenterology and Hepatology, was funded by the Edinburgh and Lothians Health Foundation and the Medical Research Council.
Dr James Dear, of the University of Edinburgh, said: "Paracetamol overdose is very common and presents a large workload for already over-stretched emergency departments.
"These new blood tests can identify who will develop liver injury as soon as they first arrive at hospital. This could transform the care of this large, neglected, patient group."