US scientists say the presence of high levels of certain chemicals may help to diagnose whether a child has been violently abused.

The scientists say adults who beat up children do not normally take their child to hospital straight away and many lie about when the injury took place.

This means chemicals released to deal with the injury after the assault have longer to build up.

Quinolinic acid, one of the chemicals, takes a long time to accumulate in the brain and the scientists, led by Patrick Kochanek of the University of Pittsburgh School of Medicine, say its presence could reveal if a parent is lying about the timing of an injury.

The chemical is secreted into the brain by immune cells after an injury.

The scientists say high levels could also indicate a history of abuse.

Chemical levels

They analysed cerebrospinal fluid taken from 39 adults and 17 children with head injuries.

Brain cells are affected by the secretion of chemicals following injury

None of the adults, who had gone to hospital within 24 hours of being injured, showed high levels of quinolinic acid.

However, two of the children had high levels. Their parents admitted they had been abused.

A third who had been abused did not have excess quantities of the acid.

Mr Kochanek said chemical levels alone could not prove child abuse, but they may be able to be used with other evidence, such as x-rays, to clinch a case.

Shaken baby syndrome

The test also included biochemicals, such as amino acids, which were also detected in high levels in child abuse victims.

For example, babies who had been badly shaken had high levels of the amino acid glutamate, which causes damage to neurons in injured brains.

The US Advisory Board on Child Abuse and Neglect says the finding shows that shaken babies may suffer more injury than those who are suffer blows to the head.

Mr Kochanek said the study is now being expanded, but the preliminary evidence was that victims of abuse usually had "a whole host of biochemical derangements in the brain".

He added: "I think it really is a reflection of how severely these infants are injured."