Many people are turning to private screening for "reassurance" over their health, an independent body has warned.
The UK National Screening Committee (NSC) has issued guidance on when people should be screened for various conditions.
It warned that too many people were putting themselves through "unnecessary" anxiety by paying for screenings they may not need and large sums were paid for such screenings, some available on the NHS.
Private screening tests can cost from £125 to £2,000.
Dr Anne Mackie, Director of Programmes at the UK NSC, said: "The safety of patients is the most important factor.
"We want to make sure that people are fully aware of the tests that are offered to them on the NHS before they pay private companies for screening that may cause unnecessary anxiety and could lead to further unnecessary investigations."
Steven Laitner, a GP and Consultant in Public Health Medicine, said there was a notable increase in private screening test offers.
He added: "However, all screening requires a careful balancing of risks and benefits of the screening tests offered. Where screening falls outside of internationally recognised criteria, it can pose a significant risk to health, leading to unnecessary anxiety, invasive testing and even unnecessary treatment without any overall health benefit."