Ok-health screening/checks is asking about the general health of a person. So you might do one before you employ someone to see if its worth hiring them. It also  can be used to describe those programmes where an employer pays for employee to have general health check to if their health is ok and to show the world that the employer cares for their staff.

Health surveillance, by contrast, is carried out to establish whether H&S controls that are established under  various regulations, typically after a risk assessment, are actually working. If this is the best   approach to testing the effectiveness of controls, then you MUST carry out health surveillance.

So is it worth doing? Yes, if your companies risk assessment process identifies that staff  are at risk of exposure to certain hazards. The sort of hazards that require health surveillance include, ionising radiation, exposure to certain hazardous substances, HAV, noise etc.

Health surveillance at its most basic does not require, medical monitoring. For example if your staff are at risk of dermatitis, it is sufficient for a manager to routinely check their hands etc to confirm that they are ok and only refer them to occupational health if there is evidence that there is something wrong .