At the moment, the blood test is usually the fourth and final stage of diagnosis.

If it were used earlier on, the researchers argue, it would also save hospitals money.

Dr Robert Roberts, of Baylor University in Texas, led the research. His team published their findings in Circulation, the journal of the American Heart Association.

Misdiagnosis

People who visit hospital believing they have had a heart attack often have to undergo many tests only to find they have indigestion, the researchers say.

The first-line tests currently in use only allow an accurate diagnosis in 4% of cases, they claim.

They say that if doctors used the blood test earlier in the diagnosis of cases of chest pain, it would cut the number of unnecessary hospital admissions.

It would also mean that patients who are currently misdiagnosed would get the treatment they really need from soon after their arrival at hospital.

Enzyme test

Doctors have known about the blood test - which looks for an enzyme called creatine-kinase MB (CK-MB) - for years.

It is the most commonly used test to confirm a heart attack has taken place.

The researchers found an ECG was not enough for accurate diagnosis

But its use has not become routine in casualty departments - the first port of call for patients suffering chest pains.

The test provides a more accurate diagnosis because CK-MB is released by dying heart cells.

Levels of CK-MB in the blood stream can therefore indicate the severity of damage to the heart and distinguish a heart attack from unstable angina.

The researchers say that, of those who attend hospital thinking they are having a heart attack, only 10% really are.

Another 20% have unstable angina - a symptom of heart disease that causes chest pain but is not as damaging as a heart attack.

Visiting hospitals

The researchers went to four hospital emergency rooms in the Houston area and took blood samples from patients who complained of chest pains.

Of 955 such patients, 119 had genuinely had a heart attack. Only 45% of these heart attacks were identified using a standard electrocardiograph.

Dr Roberts said: "Currently, physicians have the ability to make an accurate diagnosis in only 4% of those with chest pain.