NEARLY one in five NHS patients are waiting longer than the target time for treatment after being referred by doctors, figures have revealed.

The Scottish Government set the ambition of having 90% of patients beginning their treatment within 18 weeks of being referred, but new data showed performance has slumped to the lowest point since it was introduced in December 2011.

Other NHS figures showed a rise in people waiting for key diagnostic tests, while the number of patients waiting more than 12 weeks for inpatient or day case treatment has increased by almost 10,000 in two years.

The latest figures on patient referral to treatment time showed that in September, 81.4% of patients started getting help within the 18-week target, with 16,528 waiting longer than this.

Figures for July and August showed 83.2% and 82.4% started treatment within 18 weeks.

The figures do not include patients in the NHS Tayside area, as health board bosses there were unable to provide data because of reporting problems following the introduction of a new patient management system.

Of the 14 health boards who provided valid figures, only three met the 90% referral-to-treatment target in September - the Golden Jubilee Hospital in Clydebank (100%), NHS Orkney (97.5%) and NHS Western Isles (91.7%).

In NHS Grampian, two-thirds (66.6%) of patients began treatment within 18 weeks of being referred - the worst performance in Scotland that month.

Separate figures showed that at the end of September, there were 77,819 patients in the NHS waiting for a key diagnostic test - an increase of 19.2% from the year before.

Almost one in five had been waiting more than the six-week target, with tests carried out within this time for 81.6% of patients.

That means the number of patients waiting more than this time almost doubled over the course of the year, with 90.1% having tests in less than six weeks in September 2016.

More people were waiting over 12 weeks for an outpatient appointment, with figures from the end of September showing that of the 338,861 people waiting to be seen, just over two-thirds (69.7%) had been on the list for less than the target time.

There were 70,125 who had been waiting more than 16 weeks for an outpatient appointment - up from 54,677 in June and more than three times the 22,296 who waited this long in September 2015.

The number of patients waiting more than 12 weeks to be treated as either an inpatient or day patient jumped from 4,263 at the end of September 2015 to 14,191 at the end of September this year.

Health Secretary Shona Robison said the Scottish Government is "committed to delivering the investment and reform necessary to ensure our NHS is fit for the changing needs of a 21st century Scotland".

She added: "We have made an additional £50 million available to NHS boards since the spring to reduce waiting times and boards have assured us that this funding is already reducing excessively long waits for outpatient consultation.

"Alongside this, I announced £4 million for projects to introduce innovation in healthcare and improve efficiency. We expect health boards to use this funding to manage their resources and get the right balance between promptly seeing new outpatients whilst also treating existing patients who go on to require a procedure.

"We expect this improvement to be reflected when statistics for the period between October and December 2017 are published in February, with further improvement still by the spring."

Scottish Labour health spokesman Anas Sarwar claimed the NHS was "reaching breaking point due to a decade of SNP mismanagement".

He said: "The SNP government passed a law guaranteeing patients treatment within 12 weeks. The most recent figures show it is a law that is broken for one in every five patients.

"Standards for key diagnostic tests are also declining. These tests are key in detecting, identifying and then treating conditions like cancer.

"NHS staff are doing heroic work in almost impossible circumstances. Under this government they are overworked, under pressure and unquestionably underpaid. This simply is not sustainable.

"The Scottish Government cannot go on cutting the wages of NHS staff in real terms and expect patients to get the treatment Scots deserve.

"The blame for this performance lies squarely at the door of St Andrew's House. A decade of sticking plaster solutions has not worked, and the complete failure to tackle the inequalities in our country which piles pressure on the NHS should be a burning source of shame for this government."

Cancer Research UK also voiced concerns about the increasing numbers waiting more than six weeks for diagnostic tests.

Gregor McNie, the charity's senior public affairs manager in Scotland, said: "Waiting to find out if you do or don't have cancer can be an incredibly anxious time, and it's unacceptable that some people are having to wait so long for tests.

"There is increasing pressure on diagnostic services in Scotland as the number of people being referred for tests grows. For example, a national shortage of radiologists is also contributing to delays."