Why are my blood pressure readings so different?
Two readings a minute apart can differ by 10 points. Your left and right arm can disagree. Mornings run higher than evenings. Most of this is normal. Here's what's behind each pattern and when a difference is worth reporting.
Readings minutes apart
Blood pressure isn't a fixed number. It changes with every heartbeat and breath, and your body adjusts it constantly. Differences of 5 to 10 points between readings taken a minute or two apart are normal.
The first reading is often the highest. You've just sat down, the cuff squeezing is a small surprise, and you may be anticipating the number. That's why the guideline recommends taking two readings a minute apart and using both, rather than trusting one.
What not to do: keep measuring until you get a number you like. Write down the first two, and move on.
Morning and night
Blood pressure follows a daily rhythm:
- It rises in the morning. In the hours after waking, stress hormones climb and blood pressure surges. This is one reason heart attacks and strokes are a little more common in the morning, and why the morning reading is part of the home protocol.
- It falls at night. During sleep, blood pressure normally drops by around 10 to 20 percent, called "dipping".
- Some people don't dip, or their blood pressure is high at night. This is more common with sleep apnoea, kidney disease and diabetes, and only shows up on 24-hour monitoring. If you snore heavily or wake unrefreshed, mention it to your doctor.
If you take blood pressure medication in the morning, your morning reading before the dose shows how well the previous dose lasted. That's useful information, so measure before taking it.
Different readings in each arm
A small difference between arms is common. When you first start measuring, check both arms (ideally at the same time, or one right after the other):
- Under 10 points of difference in the top number is usually nothing to worry about.
- A difference of 10 points or more that shows up again and again is worth telling your doctor about. It can be a sign of narrowed arteries in the arm or upper body.
Either way, use the arm with the higher readings for your log from then on, and always use the same arm. Switching arms between readings makes your log harder to interpret.
After eating
Digestion moves blood toward your gut, and blood pressure usually adjusts within an hour or two.
- A drop after meals (postprandial hypotension) is fairly common in older adults and people with diabetes or Parkinson's disease. Feeling dizzy or light-headed after eating, especially after large, carbohydrate-heavy meals, is the clue. Smaller meals and getting up slowly can help. Tell your doctor if it happens often or you've fallen.
- A rise after meals is less common and usually has another explanation: coffee with the meal, a salty dish, alcohol, or rushing.
For your log, measure before meals rather than right after them.
Everyday things that move your numbers
| Factor | Usual effect |
|---|---|
| Caffeine | Up, for an hour or more |
| Smoking or vaping nicotine | Up, within minutes |
| Exercise | Up during and just after, often lower for hours afterwards |
| Alcohol | Can be lower for a few hours, higher the next day; regular heavy drinking raises it |
| Stress, pain, rushing | Up |
| Full bladder | Up |
| Cold room | Up; winter readings often run higher than summer ones |
| Poor sleep | Up the next day |
| Talking during the reading | Up |
| Some medicines (decongestants, NSAID painkillers) | Up |
The way to see through all this noise is to measure the same way at the same times of day, for a full week, and look at the average. A 7-day log does exactly that.
When to tell your doctor
- Your 7-day home average is 130/80 or higher.
- One arm reads 10 or more points higher than the other on repeated checks.
- You get dizzy, faint or fall when standing up or after meals.
- Your readings have changed noticeably compared with a few months ago, or since starting a new medication.
- Right away: any reading above 180/120 that stays there after a minute's rest, especially with chest pain, shortness of breath, back pain, numbness or weakness, vision changes or trouble speaking. Call 911 or your local emergency number if you have those symptoms.
Sources
- American Heart Association: Monitoring blood pressure at home can be tricky. Here's how to do it right.
- American Heart Association: Home blood pressure measurement instructions (PDF)
- American Heart Association: Understanding blood pressure readings