Do I have to tell my manager what my hospital appointment is for?

I work for a city council, whose HR department has been told by Occupational Health that they need to give me time off for hospital appointments (for something that would be a disability under the 2010 Equality Act). If I tell my manager that I have an appointment and provide proof of the date/timing, am I also obligated to tell her personally what my appointment is for, even though my employer's HR department is fully aware of it?