Thanks for your question.
High Blood Pressure is a disease that is generally treated as an outpatient. Emergency room treatment should be considered if a patient has symptoms of extremely high blood pressure, such as an altered mental status (confusion, lethargy), signs or symptoms of a stroke (paralysis of one side of the body, speech difficulty, inability to understand others), or vision changes. Of course, if you are concerned that your pressure is dangerously high and you are in danger of developing any of these symptoms, then an emergency room evaluation is in order. As far as numbers are concerned, it depends on your baseline pressure. A person with a baseline pressure of 130/70 is less likely to tolerate a pressure of 180/110, than a person with a baseline of 170/100. There is no textbook answer to this question.
The better answers are: you should see a doctor when you learn your pressure is elevated; you should not delay treatment until your pressure is extremely high; and, don't wait for any of the above symptoms before seeking medical care for high blood pressure. In other words, early treatment and ongoing follow up is essential if you have high blood pressure.
I hope this has been helpful.
Martin Cane, M.D.