Examining The Accuracy Of The First Blood Pressure Reading

Have you ever wondered why blood pressure is the first thing your doctor or nurse takes during a medical appointment?

High blood pressure (hypertension) is the leading worldwide risk factor for death.¹ Around half of all deaths related to heart disease and stroke are caused by high blood pressure, and the condition affects around one billion people.

Early signs of high blood pressure or other related diseases are difficult to detect without regular blood pressure monitoring. Multiple blood pressure readings reveal any changes, helping you get treatment as early as possible.

Solely relying on your first blood pressure reading may lead to an inaccurate diagnosis because it’s usually higher than the second reading. Your doctor or nurse should take more than one reading and compare the results for better accuracy.

How accurate is the first blood pressure reading?

The first blood pressure reading is not always accurate for a number of reasons.

The first reading often comes up higher than subsequent readings, whether you’re taking the measurement at home or having it taken in a hospital or clinic. However, reading blood pressure at home usually causes less variation.

Factors that could cause a high first blood pressure reading

These factors may explain why your first blood pressure reading is high:

1. Insufficient relaxation time

For optimal results, the American Heart Association (AHA) recommends sitting down and relaxing for at least five minutes before a blood pressure reading. Your first blood pressure reading may be higher than normal without this relaxation time.

The difficulty is that there’s very little time between patient appointments at a hospital or doctor’s surgery. By the time you walk in to see the nurse or doctor, they’re ready to get to work — you rarely get any time to relax.

What’s more, with all the noise and commotion in the waiting room, it’s unlikely you’ll get to your medical appointment feeling calm. Even if you arrive with plenty of time to spare, waiting for your name to be called is rarely a relaxing experience, and you might be feeling anxious.

2. Stress and anxiety (white coat syndrome)

When you feel anxious and worried about a medical appointment, your blood pressure may spike. This is called “white coat syndrome.”

Stress triggers the production of adrenaline and cortisol (a stress hormone), which activates your “fight or flight” response. The adrenaline rush increases your heart rate and blood pressure and provides small bursts of energy just in case you need to react to a stressful situation.

White coat syndrome may cause your first blood pressure reading to be high.

3. Incorrect body positioning

Your blood pressure reading may be high if you don’t sit in an optimal position: both feet flat on the floor with your back upright and supported. Your arm should rest on a flat surface, and the upper part of your arm should be in line with your heart.

Don’t have your blood pressure reading taken when sitting on a couch, slouching over, or crossing your legs.

Take a few seconds to check how you’re sitting before your nurse or doctor takes the reading.

4. A full bladder

Having your blood pressure reading taken when you have a full bladder can increase the reading by 10 points or more.

5. Environmental or psychological distractions

When you’re distracted, your heart starts racing, increasing your blood pressure temporarily.

You should try to be calm while your blood pressure is being measured, but it’s easy to start feeling fidgety, uncomfortable, or distracted, especially if medical environments make you nervous.

6. Alcohol, caffeine, and drugs

Alcohol, caffeine, marijuana, and other recreational drugs can temporarily increase your blood pressure. The effects can last for several hours or more, depending on the quantity consumed.

One alcoholic drink can increase your blood pressure for up to two hours, while caffeine causes your blood vessels to constrict, limiting blood flow and increasing blood pressure.

Marijuana has complex effects on the whole body, including increasing heart rate, dilating blood vessels, and raising blood pressure.

Measuring your blood pressure a few hours after alcohol, caffeine, or drug consumption will result in an inaccurate reading.

7. Talking during your blood pressure reading

Research shows that talking while your blood pressure is being measured can increase your reading by 10 to 15 points.²

Sensitive or emotional subjects cause a higher reading than general topics because they invoke an emotional reaction that can increase your heart rate and blood pressure.

Other factors that may affect your blood pressure reading

Blood pressure readings are a helpful way to keep track of your general health and wellbeing. A normal blood pressure reading is 120/80mm Hg. Any reading above 140/90 or below 90/60 is considered too high or too low.

However, even if you’re healthy, other factors can affect your reading and cause it to be too high or too low. These factors include:

1. Device type (upper arm/wrist)

Using an upper arm device to take your blood pressure gives a more accurate result than a wrist device. This is because wrist arm devices are more affected by body position.

Your wrist and arm must be positioned at heart level to get an accurate reading with a wrist device.

However, wrist devices tend to show higher numbers than upper arm devices even when you’re sitting correctly. This is because the blood vessels around the wrist are narrower and closer to the skin compared to those in your upper arm.

2. Age

Your risk of developing hypertension increases with age.³ As your blood vessels get older, they lose elasticity and become stiffer. This constricts the movement of blood through the body, increasing your blood pressure.

3. Cold temperatures

Blood pressure readings tend to be higher⁴ in cold temperatures than in warmer temperatures.

When you are in cold conditions, your blood vessels narrow to reduce blood flow to the skin. This prevents heat loss and keeps you warmer, but it also raises your blood pressure.

High blood pressure caused by cold weather is called winter hypertension.

4. Time of day

Your blood pressure is highest in the morning when you wake up due to increased sympathetic activity.

Most organ function, including brain function, slows down while you sleep to help you rest. When you wake up, your brain releases hormones (including adrenaline) to make you alert. Your blood pressure will keep rising until around noon, and then it will start to drop.

A blood pressure reading taken in the evening may read lower due to reduced sympathetic activity.

5. An empty/full stomach

Having a full stomach when your blood pressure is taken may cause a lower reading. This is because you are digesting the food you have eaten.

After you eat, your body diverts blood flow to your digestive system to help process the food. Other organ processes slow down while your blood pressure is low, causing temporary tiredness. This explains why most people feel tired immediately after eating.

People with high blood pressure are encouraged to follow the DASH diet to help lower the risk of side effects and complications.

The DASH diet contains foods like:

• Fresh fruits

• Vegetable 

• Beans

• Nuts 

• Seeds 

• Low-fat/fat-free milk products

• Whole grains

You should also try to consume more fiber-rich foods as they are known to slow the digestion process and keep blood pressure lower for longer.

6. Wrong blood pressure cuff size and placement

Most errors in blood pressure readings are caused by the blood pressure cuff size.

One study⁵ showed that a larger cuff size overestimated the blood pressure measurements by three to five points, while a smaller cuff size overestimated the results by two to six points. There was a slight variation between male and female participants.

Other studies⁶ show readings are exaggerated by more than 10 points if the cuff is positioned incorrectly and the wrong size is used. Using the correct cuff size but placing it over clothing caused little to no variance.

Should the first blood pressure reading be ignored?

A blood pressure reading taken under optimal conditions may be accurate, even if it’s your first one. However, unless you’re taking the reading on your own at home, inaccuracy is likely.

The AHA guidelines suggest two blood pressure readings should be taken one minute apart, with the average of the two measurements being used as the baseline blood pressure reading.

How to get an accurate blood pressure reading

Several factors influence the accuracy of blood pressure readings, but there are measures you can take to mitigate them. Try to take your blood pressure reading:

• First thing in the morning

• Before eating your first meal of the day 

• Before taking any medication

• With an empty bladder

• After five to ten minutes of complete stillness

• Sitting upright with both feet flat on the floor and your upper arm at heart level

Take two or more readings to get a more accurate result, and calculate the mean to get your average blood pressure reading if you get different figures. Irregular results can help you detect hypertension early enough to get treatment.

If the first reading is 140/90mm Hg or higher, more than two additional readings should be taken. If the subsequent readings are significantly lower than the first, then the first reading should be discarded.

What do the numbers mean?

You might be wondering what your blood pressure readings mean.

130–139/80–89mm Hg suggests you have stage one hypertension; 140/90mm Hg or higher indicates stage two hypertension, and a reading of 180/100mm Hg or higher means you are in hypertensive crisis and need urgent medical attention.

When to see a doctor

Be on the lookout for abnormal numbers if you measure your blood pressure at home. High blood pressure can damage your blood vessels and compromise your entire cardiovascular system, leading to serious health complications.

Seek medical attention immediately if you get an irregular reading or you experience the following symptoms:

• Chest pains

• Difficulty breathing

• Nose bleed

• Blood in urine

• Blurred vision

• Irregular heartbeat

• Severe headaches

• Unexplained fatigue 

• Confusion

The lowdown

High blood pressure is among the leading causes of death worldwide, but diagnosis can be challenging because it rarely causes symptoms. You will have your blood pressure taken during most medical appointments so your doctor can keep an eye on it and identify any changes.

Your first blood pressure reading will almost always be higher than the second due to a wide range of factors, both environmental and psychological. These factors include white coat syndrome, stress, and having a full bladder.

You can take steps to get a more accurate blood pressure reading, including being mindful about the time of day you take it. Your doctor will take two readings to get a more accurate picture of your blood pressure.

If you measure your blood pressure at home and get a reading of 180/100mm Hg or higher, get emergency medical help right away.