Regarding white coat hypertension, the shot isn’t always necessary. Some people’s blood pressure just goes up from the stress of the clinical setting.
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This prompted me to do some research, and it turns out there's very strict guidelines for how to 'accurately' measure blood pressure, almost none of which were followed by most specialists. There's a laundry list of things that can each increase your blood pressure by 10-15mmHg (eg. drinking water, sitting cross legged, recent physical exercise, not sitting with the right posture, not sitting for at least 15 minutes).
Given this lackadaisical approach to measurement, I seriously question the diagnostic validity of blood pressure tests 'in the wild'.