Railway Children is concerned by the findings of a National Crime Agency report around the potential misuse of this lesser categorisation, which indicates the missing person is not at risk.
The report, which looks at 2015/16 missing persons data, found that while some forces label all cases involving children with the higher priority category of "missing" this is not the case nationwide.
Andy McCullogh, Railway Children's policy and public affairs director, said: "It is worrying that the NCA report has identified some police forces to be still inappropriately classing all missing children from care only as absent, meaning the child is at ‘no apparent risk', when the reality is they could be at serious risk of harm.
"A quick and accurate assessment of risk is essential to ensuring vulnerable children get the help they need at the right time."
The NCA also found that record keeping around missing person reports had improved, however, inconsistencies remain.
McCullogh added that further improvements in data collection were especially vital in cases involving children.
"It is vital for police forces to gather reliable and consistent data that can be shared across police lines to fully understand the underlying reasons why a child goes missing, with a focus on prevention and early intervention," he said.
The charity is also calling for an inquiry into the way councils carry out return home interviews in cases, which can help prevent further missing incidents.
According to the NCA report children accounted for 60 per cent of missing incidents during 2015/16. Of those, 58 per cent were aged 15 to 17.
Avon and Somerset Constabulary has stopped using the category of "absent" for any cases involving children, while Northamptonshire's force has halted its use for children missing from care, the NCA report found.
In addition, Bedfordshire Constabulary stopped its use in July 2015 for all cases, including those involving adults, with all now being referred to as "missing".
While Surrey had stopped using this lesser category for children, this policy was reversed during 2015/16.
Last year HM Inspectorate of Constabulary found that most police forces did not have a good understanding of the problem of missing children in their area. This also found that cases where children were categorised as "absent" received far less attention.
Ofsted has previously raised concerns about a rise in the number of children going missing from foster care.