Breast cancer would be a good example. Mammograms have been able to pick up the disease at such an early stage that it is potentially curable. There is a good chance now that if it is detected early, the patient is more likely to die of some unrelated cause.

Early detection of other conditions, for example diabetes or obesity, allow treatment , so preventing further complications of the disease, like a heart attack.

In the old days, people only went to see the doctor when they felt sick. Now they are starting to see the doctor even when they feel well. They want to know if they have any risks for diseases , or if they are in the early stages of some diseases, where early treatment can result in a cure.

Hence, the birth of health screening as an industry. In some countries, it's a business. You can buy health screening packages, where tests are done on every part of you - blood samples, urine samples, stool samples can all be taken, and a scope can be stuffed into practically every orifice. Everything can be seen nowadays. Unfortunately, not all conditions can be detected early. And not all tests are equally good at detecting conditions.

Some tests sold as part of a complete health check-up may not necessarily exclude a condition, or reduce one's chances of dying if picked up. In fact, over-investigation may even lead to unnecessary further tests, procedures and a lot of anxiety.

So who should do health screening ? People with family histories of certain medical conditions should go before they develop symptoms. eg, a strong family history of heart attacks, certain cancers. Most people above 40 should consider getting themselves checked at least once, and then maybe 3 yearly if no problems are detected.

Companies use health screening to determine if potential employees are suitable for the job. Others use it to determine if their employees are still fit on the job. Some jobs can be dangerous for people with certain medical conditions ( would you really want a truck driver to have a history of uncontrolled fits?) , and other jobs can be dangerous for the worker's health ( eg. industries with machines that produce loud noises would need to regularly screen their workers for hearing problems).

So what about otherwise well people who are just worried and want to get tested, just to make sure ?

There are no hard and fast rules. In some countries, you pay the money, you get the test. No problem right ? Well, there are some things you may want to look out for before deciding to do the test.

Is the test safe ? Will it harm me ? Colonoscopy ( a scope inserted up your rear end to check the large intestine) has a small risk of perforation or bleeding. Your doctor needs to determine the risks versus the benefits of the test. A CT coronary angiogram ( a scan of the heart arteries to see if they are blocked) involves a lot of exposure to radiation.

Is the test easy to do ? Screening for obesity using the BMI is easy. Testing blood for high cholesterol or high sugar, is easy. So is a Pap smear for cervical cancer.

Is the test accurate ? No use doing a test if the results don't give you a good answer. eg. the blood test for the cancer marker for colon cancer may go up in other medical conditions, or not be raised in early cancer. So a "normal" result doesn't mean anything. Neither does a "raised" result.

Pap smears, mammograms, tests for BMI, blood pressure, blood sugar and blood cholesterol are reasonably accurate.

Does the test make a difference? Mammograms do detect breast cancer early enough for treatment. Pap smears detect cervical cancer in its pre-cancerous stage. Cure rates are high. So the tests are worth doing.

What is the test trying to look for ? Some people just want to have their whole body scanned in the hope of detecting some small tumour. It doesn't work that way. Perfectly healthy people may have variations in their organs, or benign cysts and growths. We don't all look the same inside. This may lead to unnecessary further tests, even operations, not to mention the terrible stress the patient has to undergo while waiting for results.

So before you go for health screening, ask you doctor about the tests you are going to do. It's good to have more knowledge about your own body. And it helps if you can take steps today to prevent diseases. But you do need to understand what you are going to do.