A review of dementia care by the Care Quality Commission has found patients moving between care homes and hospitals are likely to experience poor care.
The report Cracks in the pathway said the variations in assessing, planning, delivering and monitoring care in both hospitals and care homes puts people at risk of poor care.
The CQC inspected 129 care homes and 20 hospitals across England, looking at how care needs were assessed, planning and delivery of care, how providers worked together and how they monitored care quality.
Jeremy Hughes, chief executive at Alzheimer's Society, said: "With a staggering 90 per cent of the care homes and hospitals inspected found to have aspects of variable or poor care, this report highlights the plight that many people with dementia face."
In 29% of homes and 56% of hospitals inspected it was found that assessments were not identifying all the care needs of a patient. Staff understanding and knowledge of dementia in 27% of care homes and 56% of hospitals inspected was found to be poor or variable.
How care met people's mental, emotional and social needs was found to variable or poor in 34% of the care homes and 42% of the hospitals inspected. Sharing information was poor or variable in 27% of the care homes inspected and 22% of the hospitals inspected.
The report added that support for both physical and mental wellbeing, as well as managing known risks such as falls can help reduce visits to hospital and avoid long stays.
Following the report the CQC is to appoint a new national specialist adviser for dementia care, include a separate section in reports of hospitals on dementia care and train all inspectors to look for good dementia care.
Andrea Sutcliffe, chief inspector of Adult Social Care, said: "People living with dementia, their families and carers have every right to be treated with respect, dignity and compassion.
She added: "A wealth of guidance exists to drive the delivery of excellent care for people living with dementia. We need to make sure that every care home and hospital achieves the high standard of care we see in the best services.
"Our new approach to the regulation and inspection of health and social care means that we can celebrate good care, identify where improvements are needed and take action where necessary so that people living with dementia, their families and carers can always be confident about the care they receive."
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