One high reading does not necessarily indicate a problem, but it bears watching. Doctors do not consider you to have hypertension until you have several readings that are in the high range. Blood pressure naturally goes up and down during the day and under different circumstances. Some things that could temporarily elevate your blood pressure are stress, water retention, physical exertion and caffeine consumption. Stress definitely affects my blood pressure. It is always in the normal range when I check it on the machine at work, but the second I step into my doctor's office, up it goes.