Hospital trusts are “surprised and frustrated” by latest mortality ratios that suggest their performance has worsened.

A number of trusts are due to record a rise in their hospital standardised mortality ratios for 2008-09 - due to be published by Dr Foster in its annual Hospital Guide in the coming weeks - in spite of efforts to bring it down.

We need to get the message out there and explain that actually the hospitals in this situation have still improved

Despite thinking they had either improved safety or coding or both, and having reduced mortality rates by other measures, they have been given a higher Dr Foster ratio than in 2007-08.

This has occurred because the national mortality average has dropped significantly since last year. Dr Foster has “rebased” the ratios for 2008-09 so the “expected” mortality ratio, 100, is based on the new average.

Dr Foster director of product strategy and design Roger Taylor said hospital mortality rates in England had fallen by about 7 per cent from the previous year.

He told HSJ: “Everyone is improving but we rebase the figure to take out the improvement that happens across the board.”

Several trusts have told HSJ they are concerned it will be incorrectly interpreted by the public as a sign their safety and service quality is getting worse.

Mr Taylor acknowledged a rise in mortality ratios could be misinterpreted by non-experts, and that could be “slightly frustrating”, adding: “We need to get the message out there and explain that actually the hospitals in this situation have still improved.”

A source told HSJ at least six acute and foundation trusts had been surprised by an increased mortality ratio.

Colchester Hospital University Foundation Trust medical director Andrew May said his trust had worked on improving its 2007-08 result of 104.1. However, he said the 2008-09 figure was 112.

He said: “We are not complacent about it - we are conducting a very intensive programme of improving patient safety and quality and won’t be satisfied until we are under 100. We monitor mortality daily and follow up where there is any cause for concern.”

The trust has also been making coding improvements, Mr May said. However, he said there was a “presentational issue” of the figure being interpreted as reflecting worsening safety.

Another hospital trust chief executive told HSJ it was “frustrating” to receive a higher mortality ratio despite improving safety and quality.