Which finger should never be used to determine a pulse?

The thumb should never be used to determine a pulse primarily because it has its own pulse, which can interfere with the assessment of another individual's pulse. When attempting to palpate a pulse, such as the radial pulse, using the thumb may lead to confusion because the pulsations from the thumb can be mistaken for the pulse of the person being examined. This can result in an inaccurate assessment of the patient's condition.

In contrast, the index, middle, and pinky fingers do not have significant pulses of their own that would affect the palpation of another person's pulse. Therefore, using one of these fingers is recommended for accurate measurement of heartbeats.