Mr Smith’s parents Leila and Errol said “to this day we still can’t accept that Darnell’s not here any more”.

In a statement issued through their solicitors, Irwin Mitchell, they said: “He was our beloved boy and our lives were dedicated to looking after him. There’s not a day goes by when we don’t miss him.

“Sickle cell disease is a complex condition and we feel like there’s still not enough known about it and how to care for someone living with it, particularly those who also have learning difficulties like Darnell did.”

The Sheffield Teaching Hospitals NHS Foundation Trust said it was implementing a new electronic patient care record system this year, which would ensure all patient records were more readily accessible to its staff.

The trust’s medical director, Dr Jennifer Hill, said: “I would like to apologise again that we did not carry out Darnell’s observations as frequently as we should have done, and that his individualised care plan was not immediately visible to staff.

“I know that we cannot take away the pain that Darnell’s family are feeling, but I hope that I can reassure them that we have learnt from this and are taking actions to limit the chances of this happening again.”

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