Should You Take Your Blood Pressure When You're Sick?

Yes, if measuring is part of your routine or your clinician asked you to track it. Just treat sick-day readings as their own category. Fever, pain, a bad night and some cold remedies can push your numbers up, while vomiting or diarrhea can pull them down, so a reading taken while you're ill tells you about the illness more than about your usual blood pressure.

On the pressure side, Mayo Clinic says decongestants are the cold medicines of most concern for people with high blood pressure, because they can raise it, and some anti-inflammatory painkillers can too. Pulse moves even more predictably. A 2021 study in Critical Care Medicine by Broman and colleagues analysed 472,941 paired temperature and heart rate readings from 9,046 intensive care patients and found that each 1°C rise in body temperature came with a heart rate about 8.35 beats per minute higher (7.24 in men, 9.46 in women). Those were ICU patients, not people at home with flu, but the direction holds. Being ill doesn't change the safety line, though: the AHA treats any reading above 180/120 as urgent, sick or not.

What changes your reading when you're ill?

Being sick rarely changes just one thing. You might have a temperature, a sore throat, poor sleep and a decongestant in your system all at once, and each pulls the reading in its own direction.

If your monitor shows a heart rate well above your normal on a feverish day, that fits the pattern in the table. Our guide to the heart rate on your monitor explains what that third number means.

Should you skip your reading when you're sick?

You don't need to. If your clinician asked for daily readings, keep taking them. Skipping sick days leaves gaps in the log, and a labelled reading is more useful to them than a missing one.

What you shouldn't do is read a trend from those days. A week with a fever can make your average look higher than it really is. Day-to-day changes are normal anyway, as our piece on why readings vary shows, and illness simply adds more of them.

How to get a fair reading on a sick day

The aim is the same as any other day: a calm, comparable number. A few changes help when you're unwell.

• Wait until you can sit still comfortably for about five minutes, back supported and feet flat. Don't measure straight after a coughing fit, a hot shower or a trip to the bathroom when you feel shaky.
• Take two or three readings a minute apart, as the American Heart Association suggests, and record them all.
• Add a note to each reading: your temperature if you took it, your main symptoms, and any cold remedy or painkiller you had that day.
• Use the same arm and cuff you always use, so the only thing that's changed is you.

Once you're well again, go back to your normal schedule. For a fair comparison with your pre-illness numbers, a common home-monitoring routine works well: 2 readings a minute apart, morning and evening, for 7 days gives you 28 readings, the same routine our guide to how many readings to average uses.

Cold medicine, painkillers and your numbers

Mayo Clinic notes that decongestants such as pseudoephedrine and phenylephrine can raise blood pressure and can stop some blood pressure medicines from working as well. It also lists NSAIDs, such as ibuprofen and naproxen, among the medicines that can raise blood pressure in some people, and it points out that some products are high in sodium.

That doesn't mean you can't treat a cold. Mayo Clinic's advice is to read labels and ask a pharmacist or doctor which product suits you, and that conversation is easiest before you buy. If you already take blood pressure medication, don't change, skip or stop any of it on your own because you're unwell. Some medicines come with sick-day instructions, so the person to ask is your prescriber or pharmacist. If an illness makes it hard to take your usual medicines, or you aren't sure what to do, call your prescriber or pharmacist and let them decide.

Which numbers matter while you're ill?

Under the ACC/AHA guideline, high blood pressure starts at 130/80, while ESH and NICE use 140/90 for clinic readings. A single sick-day reading above either line isn't a diagnosis, but a pattern that stays high after you've recovered is worth raising with your clinician.

Lower than usual readings deserve attention too. If you're dizzy or light-headed after days of vomiting or diarrhea and can't keep fluids down, contact your healthcare professional. Fainting, confusion, or a racing heart with cold, clammy skin need urgent care, as the NHLBI notes for severe low blood pressure.

When is a sick-day reading an emergency?

A very high reading isn't something to blame on the flu. The AHA says a reading above 180/120 (either number is enough) needs attention right away. If you also have chest pain, shortness of breath, back pain, numbness, weakness, vision changes or trouble speaking, don't re-measure: seek medical help immediately and call emergency services.

With no symptoms, rest about five minutes and measure once more. If that repeat is still above 180/120, seek medical help immediately rather than measuring again to see whether it settles. Chest pain or trouble breathing during any illness needs urgent care whatever the monitor says.

Keeping sick days separate with BPlus

BPlus makes the labelling quick. Log systolic, diastolic and pulse by hand, or scan your own monitor's display with the camera, and the time, date and arm are added for you. Add a note such as "fever, took cold tablets" to any reading, then use the trend charts and searchable history to compare those days with ordinary ones. A PDF or CSV report gives your clinician the whole picture.

Medication reminders can help you keep to the routine your prescriber set when a cold scrambles your day. Your data stays on your device, the app works offline, and there's no account to create. BPlus is a wellness and logging tool, not a medical device: it doesn't measure, diagnose or treat blood pressure, and it's no substitute for professional care.

Mini-FAQ: blood pressure when you're sick

Does a cold or flu raise your blood pressure? It can, usually for a short time. Fever lifts your pulse, and pain, poor sleep and coughing can nudge pressure up. Decongestant cold remedies can raise it too, according to Mayo Clinic. Most effects fade as you recover, but a very high reading still needs acting on, as the emergency section explains.

Does a fever affect a blood pressure monitor? It mostly shows up in the pulse. In a 2021 study of 9,046 ICU patients, each 1°C rise in temperature came with a heart rate about 8 beats per minute higher. That study measured heart rate, not blood pressure, so note your temperature next to each reading.

Should I keep taking my blood pressure medicine when I'm sick? Don't change, skip or stop it on your own. If vomiting, diarrhea or anything else makes it hard to take your usual medicines, call your prescriber or pharmacist. It also helps to ask them, while you're well, what they'd want you to do on a sick day.

Can being sick make blood pressure low? Yes. Vomiting, diarrhea and not drinking enough can leave you short of fluid, and readings can run lower than usual, often with dizziness when you stand. If you can't keep fluids down, contact your healthcare professional. Fainting or confusion needs urgent care.

Sources

• The Relationship Between Heart Rate and Body Temperature in Critically Ill Patients (Critical Care Medicine, 2021, PubMed)
• Mayo Clinic: High Blood Pressure and Cold Remedies: Which Are Safe?
• American Heart Association: Monitoring Your Blood Pressure at Home
• American Heart Association: When to Call 911 for High Blood Pressure