NHS Scotland is hitting one out of the eight key performance targets set by the Scottish Government.

Too many patients are waiting too long for hospital appointments, operations and cancer treatment according to ministers' own standards.

Public spending body Audit Scotland said health boards were finding it "increasingly difficult" to deliver some of the pledges - noting the targets had become more challenging at the same time as the squeeze on public finances.

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Their report, which gives an overview of the state of the Scottish health service, also said: "Boards' declining performance against hospital waiting times targets is an indication of the building pressures they are facing from increasing demand."

Some health boards have reported difficulties both delivering the targets governing timeous treatment for patients and keeping their budgets in the black. The Audit Scotland report said NHS Ayrshire and Arran, NHS Lothian and NHS Grampian "have agreed with their boards that they face risks in continuing to achieve performance targets while remaining in financial balance."

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Ensuring patients with drug and alcohol problems start treatment to support their recovery within three weeks is the only target which NHS Scotland is delivering, according to the auditors. Children and teenagers with mental health problems are not being seen quickly enough with around 15 per cent waiting more than 18 weeks for appointments in March this year. This represents a slump compared to previous years. In 2013 around 96 per cent of troubled young people were seen within the time frame.

The number of cancer patients who start treatment within two months of their referral to hospital has also deteriorated. However, 94.9 per cent do begin therapy within a month of their treatment plan being agreed. This almost hits the 95 per cent goal.

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Audit Scotland said the pressure on health boards to meet the targets "does not help" the Scottish Government's plan to shift the balance of care away from hospitals towards community prevention services.

The Scottish Government has commissioned a review of the national targets it has set for the NHS.