The £50 test could save hundreds of lives a year and help reduce the £3.5bn cost of alcohol-related harm to the NHS, its creators said.
GPs can use the test, developed by researchers at the University of Southampton, to score high-risk patients' likelihood of developing liver fibrosis and cirrhosis.
Their study found two-thirds of harmful drinkers given a 'red' score - reflecting a high risk of serious liver disease - reduced the amount of alcohol they drank to healthier levels.
The Southampton Traffic Light (STL) test combines several different tests and clinical markers to estimate present liver damage and future risk of serious disease.
A red result means the patient probably has liver fibrosis and may have cirrhosis. Amber means a 50% chance of fibrosis and patients should reduce alcohol consumption. Green means there is no cirrhosis and complications from liver disease over the next five years are unlikely.
The study, funded by the National Institute for Health Research, offered the test to 393 heavy drinkers in GP surgeries. Forty-five patients, around 12%, received a red score, while 40% had an orange result and 49% a green result.
Of the 52% with a red or amber result, 65% reduced drinking to non-harmful levels. Only half as many of those with a green result reduced the amount they drank.
Lead author Dr Nick Sheron, a consultant hepatologist at Southampton General Hospital, said: 'Patients are developing alcohol-related liver disease in the community but it is not being picked up until they are admitted to hospital, by which time it is too late for many of them.
'It is possible that hundreds of lives could be saved by having a simple test, like the STL test, available in the community, not to mention NHS resources.'
Co-author and GP Dr Michael Moore said: 'In primary care, minor abnormalities of existing liver tests are quite common but we struggle to know how best to investigate these further and who warrants specialist intervention.
'The traffic light test has the advantage of highlighting those at highest risk who should be investigated further and those in whom the risk is much lower where a watchful approach is more appropriate.'