Health screening is a double-edged sword that needs to be wielded discriminately.

Used appropriately at clearly defined targets, it pinpoints and slays diseases ("Make health screening compulsory and free under MediShield Life"; last Thursday). Swung around wildly, it causes untold collateral damage ("Compulsory health screening could raise costs" by Mr Chan Yeow Chuan; last Friday).

Better and earlier recognition, diagnosis and management of diabetes, high cholesterol and hypertension are estimated to have added 10 years of longevity to Singaporean lives over the last four to five decades.

Mass screening for these diseases is cost-effective in maintaining quality of life.

But screening for cancers must be more targeted.

For instance, colonoscopies are very effective for patients aged 50 and above, younger patients with familial histories of colon cancers, and those known to have intestinal polyps.

Colonoscopies done just as a "precautionary measure" tend to be just money padders for gastroenterologists.

Similarly, regular mammograms for women aged 40 to 50 are recommended only for those with a familial predisposition, who have had a previous disease or who are on long-term contraceptive use.

Otherwise, the more mammograms are done in mass screening exercises, the greater the chances of some pathology being reported, with resultant mental anguish and unnecessary operations as a consequence.

Even Pap smear screening for cervical cancer would be more cost-effective and just as efficacious if done biennially rather than annually.

Not all screening procedures are equal. Some have dubious value, some are useful if targeted at the vulnerable and susceptible, and others are useful if done at the right frequency.

But we should have no reservations about the standard basic health screening, which is proven straight and true.

Yik Keng Yeong (Dr)