Low blood pressure is generally considered a reading below about 90/60 mm Hg (millimeters of mercury), according to the Mayo Clinic. The top number shows pressure when the heart beats; the bottom shows pressure between beats. A low reading is not always harmful, especially if it is usual for you and you feel well. Symptoms, sudden drops, and your medical history help determine whether the reading needs attention.
How should you read a low blood pressure result?
Blood pressure is written as two numbers, such as 110/70 mm Hg. The first number is called systolic pressure, which measures the force of blood against artery walls when the heart contracts. The second number is called diastolic pressure, which measures that force while the heart relaxes between beats.
A reading below 90/60 mm Hg is commonly used as the general reference point for low blood pressure, also known as hypotension. However, this number is not a universal cutoff for everyone. Healthcare professionals consider the reading as a whole, whether it is different from your usual blood pressure, and whether you have symptoms.
Is low blood pressure always a cause for concern?
No. Some people naturally have lower blood pressure and feel completely well. For them, a consistently low reading may be normal and may not require treatment. The American Heart Association explains that one reading lower than usual is not generally a reason for alarm when there are no concerning symptoms or other problems.
What matters is the pattern and circumstances. A reading that has been similar for years may have a different meaning from a sudden drop, particularly if it occurs with dizziness, weakness, or fainting. Blood pressure can also change throughout the day with body position, activity, meals, fluid intake, and medicines.
If your readings are repeatedly lower than expected, compare them with your usual results and note when they occur. A record of readings, symptoms, and circumstances can help a healthcare professional decide whether further evaluation is needed.
What symptoms can occur with low blood pressure?
When blood pressure is too low for the body's needs, a person may experience symptoms such as the following. The NHS identifies these as possible experiences associated with low blood pressure:
- Dizziness or feeling lightheaded
- Blurred or temporarily reduced vision
- Nausea or an upset stomach
- Weakness or unusual tiredness
- Difficulty concentrating
- Fainting or feeling close to fainting
These experiences can have causes other than low blood pressure. Their timing is useful information, especially when symptoms begin after standing up, occur repeatedly, or interfere with everyday activities. Fainting, persistent dizziness, or symptoms that are becoming more frequent warrant medical assessment.
What can cause blood pressure to become low?
Blood pressure may be naturally low, or it may fall because of a temporary change, a medicine, or an underlying health problem. The Mayo Clinic describes several possible causes, including dehydration, pregnancy, certain heart conditions, hormonal disorders, and some medicines.
- Dehydration: Losing fluids through vomiting, diarrhea, fever, or other circumstances can reduce the amount of fluid circulating in the body.
- Medicines: Blood pressure medicines, diuretics, some heart medicines, and certain other drugs can contribute to lower readings.
- Pregnancy: Changes in blood vessels during pregnancy can cause blood pressure to fall.
- Heart-related conditions: Certain heart rhythm problems, heart valve conditions, and heart failure may affect blood pressure.
- Hormonal or other medical conditions: Some endocrine disorders and other illnesses can affect blood pressure regulation.
- Major blood loss or serious illness: Significant bleeding, a severe infection, or a serious allergic reaction can cause a sudden and dangerous fall in blood pressure.
The cause cannot be determined from the blood pressure number alone. A healthcare professional may review your medicines, recent illnesses, fluid loss, pregnancy status when relevant, and medical history to understand the change.
Why might blood pressure drop when you stand up?
Blood pressure can fall when a person moves from lying or sitting to standing. This is called orthostatic, or postural, hypotension. A brief change in position can sometimes cause temporary lightheadedness, but repeated or persistent episodes may need evaluation. It is possible to have this problem even when a blood pressure reading taken while sitting appears usual.
The Merck Manual Professional Edition describes how clinicians assess blood pressure changes after standing. They may compare readings taken while lying down and at set intervals after standing, while also checking symptoms, pulse, medicines, and possible contributing conditions. This is more informative than relying on a single reading taken at home.
Position-related blood pressure changes are more common in older adults. They can also occur in younger people, including when dehydration, medicines, or other factors affect circulation. Recurrent dizziness on standing should be discussed with a healthcare professional, particularly if it increases the risk of falls.
How does age affect what is considered low blood pressure?
The 90/60 mm Hg reference point is commonly used when discussing low blood pressure in adults, but blood pressure interpretation in children requires age-appropriate assessment. According to the Merck Manual Professional Edition's guidance on blood pressure in children, expected blood pressure values vary with age, sex, and height, especially in children younger than 13 years. The adult reference point should therefore not be used on its own to assess a child.
Older adults may be more likely to experience blood pressure drops when standing or after eating. Medicines and other health conditions can contribute to these changes. For an older person, a new low reading accompanied by dizziness, fainting, or falls deserves particular attention because a fall can cause injury.
When should you seek medical attention for low blood pressure?
Arrange a medical assessment if low readings occur repeatedly, if you regularly feel dizzy or weak, or if symptoms happen when you stand up. It is also important to seek advice when blood pressure changes after starting or adjusting a medicine. Do not stop or change a prescribed medicine on your own; a healthcare professional can assess whether an adjustment is appropriate.
Seek emergency medical help if a sudden fall in blood pressure occurs with signs of a serious problem, such as new confusion, cold and clammy skin, rapid shallow breathing, or a weak and rapid pulse. Fainting with incomplete recovery, major bleeding, or a suspected severe allergic reaction also requires urgent attention. These signs may indicate that the body is not receiving enough blood flow.
How is a low blood pressure reading evaluated?
A healthcare professional usually begins by reviewing your blood pressure readings, symptoms, medical history, and current medicines. They may repeat the measurement and check blood pressure in different positions if symptoms are associated with standing. The timing of symptoms and whether the readings have changed from your usual pattern can help guide the assessment.
Additional examination or tests may be recommended when the history suggests dehydration, blood loss, a heart problem, or another underlying condition. Treatment depends on the cause and whether low blood pressure is producing symptoms. People who consistently have low readings but feel well may need only routine monitoring, while others may require treatment of an underlying problem.
What can you do after getting a low reading?
If a reading is unexpectedly low but you feel well, repeat the measurement after resting and record the result. Note the time, your body position, any symptoms, and whether the reading differs from your usual results. Discuss repeated low readings with a healthcare professional rather than relying on a single number to decide what they mean.
If you feel faint or dizzy, sit or lie down to reduce the risk of falling. Seek help if symptoms persist, recur, or worsen. Increasing salt intake or changing medicines is not appropriate for everyone, so discuss ongoing measures with a healthcare professional, especially if you have a heart or kidney condition or take medicines that affect blood pressure.