An estimated £100m is spent on health MOTs
Private health checks offer poor value for money and can lead to painful and often possibly dangerous tests, a consumer group says.
An investigation by Which? found that the firms behind the "health MOTs" even offered conflicting advice.
The group said all too often the tests, which cost an average of £423, were just catering to the "worried well".
But some of the health firms highlighted said their tests were good quality and provided value for money.
An estimated £100m a year in the UK is spent on health MOTs, which include physical tests as well as blood pressure and cholesterol checks.
Which? researchers posed as customers at clinics run by six health firms as well as talking to others and surveyed more than 4,000 members of the public before running the findings past a panel of experts.
They found prices ranged from £125 to £2,000.
One researcher was given conflicting advice about his risk of heart disease, despite getting almost identical test results.
BMI healthcare said he had a greater risk than average for his age and should take immediate action, Nuffield Health said his risk was in line with expectations for his age and Bupa said his heart was much better than average.
Which? also found that none of the clinics visited talked about the possible downsides of testing, including false positives.
The report also warned that the tests being carried out often led to unnecessary and sometimes painful further checks.
For example, for every 1,000 people who have a urine test, 50 will need further investigation, but only 1.5 will actually have a problem requiring treatment.
Value for money
Martyn Hocking, from Which?, said: "Health MOTs often cater for the 'worried well' who want the reassurance of a clean bill of health, but they can cost hundreds of pounds for what sometimes amounts to little more than lifestyle and dietary advice.
"That might seem harmless, but if the tests flag issues that turn out to be false alarms you could actually end up with unnecessary worry, rather than the peace of mind you signed up for."
Dr Peter Mace, from Bupa, said: "We don't see the 'worried well'. We see people who are interested in their health and want to take positive steps to improve it and understand their own health and health risks."
A spokesman for BMI Healthcare added the company was "dedicated to delivering the highest quality" care.
"We firmly believe that our assessments are good value for money and can deliver positive, life-changing benefits to our patients."
And Nuffield said its tests were "incredibly important" in tackling problems such as diabetes and heart disease.