One-third of SIDS deaths appear to be linked to elevated levels of serotonin, according to a new US study.

A significant and potentially life-saving step forward in SIDS research has been made by scientists in the US.

A study published in the Proceedings of the National Academy of Sciences has found one-third of SIDS deaths appear to be linked to elevated levels of serotonin - a chemical that helps regulate breathing, heart rate and the ability to wake up.

The finding points to the possibility of a preventative blood test being developed to screen babies for SIDS, Australian child sleep expert and researcher Professor Karen Waters says.

"Ultimately we want to find some sort of biomarker to tell us which kids are at risk and so this is really the first one that's come out," Prof Waters told AAP.

"That's exciting."

Researchers at Boston Children's Hospital and Harvard Medical School tested the blood of 61 babies who had died of SIDS.

They found one-third had higher-than-normal levels of serotonin in their blood serum.

In Australia in 2013, 117 babies died suddenly and unexpectedly, with 54 identified as SIDS cases.

Despite these deaths, SIDS is rare and the risk of a baby dying from it is low. Most deaths happen during the first three months of a baby's life.

Professor Waters from the University of Sydney and Children's Hospital at Westmead has spent the past 10 years studying the neuropathology of the brain stem in SIDS.

She says the recent research suggests there is some abnormal metabolism of the serotonin.

"They did look a bit at whether it's broken down more slowly and there was no suggestion of that, so it seems to be an abnormality in the production," Prof Waters said.

Clearly, a lot more research is needed to improve understanding, she said, but described the discovery of a blood marker that could detect SIDS as "huge".

"It's exactly what you want to find if you are doing a test," she said.

"You want to catch the kids before they die, so a marker like this is exactly what you want to try to find."