Parents doing home renovations on pre-1970s houses covered in toxic lead paint could be unwittingly putting their children at risk, while doctors are relying on "obsolete" guidelines that allow dangerously high levels of lead in the blood.

Children living in suburbs with high concentrations of pre-1970s houses, such as Marrickville, Randwick and Ku-Ring-Gai council areas, are particularly at risk of lead poisoning, the researchers say.

In a letter published in the Medical Journal of Australia, they claim 100,000 children aged up to four could have lead levels in their blood putting them at risk of behaviour problems and lowered IQ.

Co-author Mark Taylor, a professor of environmental science at Macquarie University, said houses in inner cities such as Sydney were "riddled with lead".

He said scientists had discovered even low levels were linked to dangerous health outcomes as levels in the community decreased. Australia's peak health body, the National Health and Medical Research Council, currently recommends Australians have blood levels below 10 micrograms per decilitre of blood.

But Professor Taylor said the US National Toxicology Program had released a review earlier this year finding lead levels half as high caused decreased academic achievement, IQ and cognitive measures as well as increased incidence of attention-related and problem behaviours.

While such changes could be small enough to not be immediately identifiable by doctors, spread across the population they could have a massive effect.

"A million kids losing a million IQ points - that's a lot of IQ down the drain," he said.

The review also found some evidence of decreased kidney function and delayed puberty in children under 12.

Professor Taylor's co-author, Chris Winder, a professor of toxicology and occupational health at the Australian Catholic University, said the council was taking too long to review the evidence and set new standards for blood lead levels.

"The evidence is overwhelming and the NHMRC should roll up their sleeves and do something, rather than having this long ponderous process,'' Professor Winder said.

There are no reliable up-do-date studies of Australians' lead levels. To estimate them, the group used US rates of blood lead levels above 5 micrograms per decilitre, and applied them to the Australian population.

Professor Winder said it was not possible to define exactly how and why children get exposed to lead, as it could occur in many ways including contaminated dust, soil or house paint.

Elizabeth O'Brien, the founder of the advocacy organisation The Lead Group, said it was only in 2010 that adding lead to paint was completely banned.

She said a national study of exposure levels was urgently needed. "We can only guess how many children and adults are suffering from high blood lead levels that are impacting on their health," she said.

She said parents and doctors were often unaware of the problem and did not think to test for it.

A spokesman for the National Health and Medical Research Council said it was never intended that the goal of 10 micrograms be interpreted as a ''safe'' level of exposure.

"Having said that, the statement and its supporting evidence is currently under review, [and] all children should have their exposure to lead minimised," he said.