An investigation has been launched after apparently unusually high death rates at Mid-Staffordshire NHS Foundation Trust.

The health watchdog said it was investigating the Trust after data showed the rates were "out of normal range". It is focusing closely on patients admitted to the trust as emergencies. And it will investigate the quality of care provided across the trust, in particular to older people, after patients raised concerns.

The trust said today it believed its rates were normal for a trust of its size and the population it serves. It released figures showing its standardised mortality rate (SMR) was 127 in 2005/06.

Nationally, the SMR is set at 100 so any figure above this reveals a higher than expected death rate.

The trust said its SMR was down to 101 between May and October 2007, with an SMR for emergency admissions over that time period of 100.4.

Regarding the 127 figure, the trust’s chief executive, Martin Yeates, said: "We worked with the Strategic Health Authority and investigated this apparently high mortality rate and concluded that it was due to problems in the way we were recording and coding information about patients.

"We have, over the last year, employed more clinical coding experts to work within the various specialty departments to help staff to record information and improve the quality of data.

"As a result, there has been a significant improvement in our SMR and our processes have been confirmed as being appropriate by our internal auditors."

But the Healthcare Commission said it would investigate the issue itself after an alert system suggested a higher than normal death rate among the data. It visited the trust on two occasions and requested evidence before deciding to launch an official investigation.

Nigel Ellis, the Commission’s head of investigations, said: "An apparently high rate of mortality does not necessarily mean there are problems with safety.

"It may be there are other factors here such as the way that information about patients is recorded by the trust. Either way it does require us to ask questions, which is why we are carrying out this investigation."

The inquiry will also look at governance protocols for protecting the safety of patients at the two hospitals managed by the trust - Cannock Chase and Stafford.

Mr Ellis said: "It is absolutely critical that, on behalf of patients, we get to the bottom of these issues and bring clarity to the data on mortality rates.

"The figures at Mid Staffordshire Foundation Trust are out of normal range which is why we are carrying out this investigation to get a clear picture of what is going on.

"People using the trust’s hospital services, should be assured, however, that if we thought the trust was unsafe we would have already taken action.

"There is no cause for immediate alarm. The safety of patients is our number one priority, nothing will get in the way of this."

Mid Staffordshire became a foundation trust in February. Beforehand, it was the Mid Staffordshire General Hospitals NHS Trust.

It scored "fair" on quality of services in the Commission’s annual health check last year from across a possible rating of weak, fair, good or excellent.

The trust met core standards and existing national targets but failed against a set of new targets, including working towards substantially reducing death rates from heart disease and stroke and related diseases by 2010.

It serves around 300,000 in people in Stafford, Cannock, Rugeley and the surrounding rural areas of South Staffordshire.

Mr Yeates said: "We are co-operating fully with the Healthcare Commission’s investigation into our trust and will supply all the information and support its team needs to complete its enquiries.

"I would like to repeat the Healthcare Commission’s statement that if our services were unsafe they would have taken action already - and therefore local people may rest assured that we will continue to provide our full range of services.

"It will be business as usual in our hospitals and I can assure our patients, their families and the general public that our drive to improve services continues - and our services are safe."

The trust has set up a helpline for anyone with concerns - 08000 407060 - between 8am and 8pm Monday to Friday.