A US study has found a new blood test which can detect traumatic brain injuries faster, cheaper and with more accuracy than standard emergency department scans.

A new blood test has been developed which can quickly diagnose a concussion, even among cases where standard scans have not detected any problem.

A US study has found by measuring protein levels in the blood, the test can detect traumatic brain injuries often missed by emergency departments.

Currently, doctors physically examine a patient for concussion symptoms before ordering a CT scan.

However researchers found it failed to detect signs of injury among 30 per cent of patients.

A MRI scan is more accurate but not every hospital has a machine and results are much slower - and more expensive.

Lead researcher Geoffrey Manley, from the University of California, said the blood test could help doctors treat patients with suspected traumatic brain injury both "quickly and accurately".

It could also help pinpoint the type and extent of the damage.

Published in Lancet Neurology, the study found cells damaged by a concussion release glial fibrillary acidic proteins, which leak out of the brain and into the bloodstream.

Among patients who had higher levels of protein in their blood, about 64 per cent were later found to be suffering a concussion.

The new test could have come in handy for Cricket Australia after its sports medicine boss came under fire for his handling of Steve Smith's injury.

Smith missed out on playing the third Ashes Test against England after being diagnosed with a delayed concussion.

Sports medicine manager Alex Kountouris defended the decision which allowed Smith to return to bat after he was struck in the neck by a ball on day four of the second Test.

The batsman had to undergo repeated testing for concussion over 24 hours until his condition deteriorated enough for symptoms to emerge.