Blood pressure readings can vary in a single person throughout the day depending on the situation. Factors such as stress, anxiety, foods eaten (caffeine or salt intake), smoking, or exercise can cause pressure to rise.
The American Heart Association defines a normal blood pressure as less than 120/80. Pre-hypertension ranges between 120/80 and 139/89, and high blood pressure is 140/90 and higher. In pregnancy normal blood pressure should be below 120/80.
If your blood pressure reaches into the high range, you should see your doctor about lifestyle modification and possibly medication especially if you have other risk factors, such as diabetes or heart disease.
High blood pressure (for example, 180/110 or higher) may indicate an emergency situation. If this high blood pressure is associated with chest pain, shortness of breath, headache, dizziness, or back or abdominal pain, seek medical care immediately. If you are experiencing no associated symptoms with a high blood pressure reading such as this, re-check it again within a few minutes and contact your doctor or go to an emergency room if it is still high.
If your blood pressure is lower than about 100/60 you may have low blood pressure, depending on the associated symptoms. If you are unsure, check with your doctor.