Q: Are off-the-shelf automatic blood pressure monitors accurate and reliable? How do they compare with a doctor's manual method of measuring blood pressure?

Also, why do doctors take blood pressure twice? Which reading do they take - the first, the second or the average reading?

I find that my blood pressure measured by the automatic blood pressure monitor is always higher than when taken in a doctor's clinic. Why is this so?

Finally, I understand that blood pressure goes up during physical exercise. Is that bad for the body?

A: Automatic blood pressure monitoring sets sold in the market may have different mechanisms of detecting and determining blood pressure. Manufacturers typically would have done validation tests in their laboratory on people with normal and elevated blood pressure before calibrating their machines.

The testing methodology and results should be available upon request or online. In general, these machines provide accurate readings.

Comparison with the doctor's blood pressure readings in the clinic is by no means easy, as a 'white coat' phenomenon can occur. This is when patients exhibit elevated blood pressure in a clinical setting but not in other settings. This may be due to the anxiety and stress felt by some patients during a clinic visit. This discrepancy can be marked at times.

In the ideal setting, where the person is calm, relaxed and rested, the two blood pressure readings (by automated machine or doctor) should approximate each other.

Doctors tend to take blood pressure twice because the first reading may be affected by anxiety.

Studies have also shown that repeated blood pressure taking can help reveal the 'actual' blood pressure. As a general rule, the first reading (usually higher) is discarded and the second one taken.

Blood pressure increases correspondingly to the intensity of the physical activity, according to the needs of the body and the cardiovascular system. This change is considered physiologic or normal.

Without this increase, the body is unable to perform exercises. In some people, the blood pressure rise is overwhelming, that is, above 200/110mmHg. This can be unhealthy and potentially dangerous, especially if it goes even higher. -Dr. Raymond Wong

This article was first published in Mind Your Body, The Straits Times.