This is a very personal question as there are a whole suite of health insurance products on the market, all with different levels of cover, varying limits and policy terms.
For your specific plan it is important to consult either your adviser or your insurer directly to ensure you clearly understand what is and is not covered under the plan.
Most insurers offer a number of products which can fall in one of three broad categories. These start out as a basic health insurance plan which will only provide cover for more serious treatment where you require a stay in hospital. Such a plan may limit the level of inpatient treatment you receive and is not likely to offer any form of outpatient treatment.
A mid range option will provide a level of cover for both inpatient treatment and outpatient treatment.
Inpatient treatment will often be covered in full where you will have a monetary cap such as £1,000 per policy year on outpatient treatment such as scans, diagnostics tests and consultations.
Broadly speaking most Comprehensive Health Insurance plans will cover both inpatient treatment and outpatient treatment in full with a number of additional benefits thrown in to the mix.
However, as mentioned, each insurer has their own products which often have a number of options to choose from so to truly understand your policies limitations you will need to read through your policy terms and discuss with your adviser or the insurer.