A health screening should always involve a medical consultation (Doctor fined $10k over error in cancer patient's health report; June 6).

First, patients with symptoms such as a change in bowel habits should be referred for specialist evaluation, rather than going through a routine screening.

Second, the interpretation of medical investigations requires medical knowledge.

A normal test does not necessarily mean the absence of disease, and an abnormal test does not necessarily mean the presence of disease.

For instance, many patients with liver cancer have normal alpha-fetoprotein (a marker for liver cancer) levels.

In contrast, elevated prostate specific antigen (a marker for prostate cancer) levels do not necessarily mean the presence of prostate cancer.

Third, not all tests on the screening panel are recommended for everyone. For instance, mammograms are generally not recommended for young women, as these may show false positive results.

Fourth, there are uncertainties around incidental findings, such as nodules or cysts in the liver and the kidneys, which will lead to more anxiety for those screened and higher costs for further investigations.

Health screenings should always be done in conjunction with a medical consultation to ensure the right tests are done, and the correct interpretations are made.

It is time the authorities tighten regulations on centres offering health screenings to the public.

Desmond Wai (Dr)