Commonly used arm positions can overestimate blood pressure readings: study

Also doctors and nurses are known to do an abject awful job of measuring bp according to the defined procedure. It’s usually way off when taken clinically.

Ars article here but there’s plenty in pubmed too.

https://arstechnica.com/health/2024/10/your-doctors-office-c...

[edit] The prep guidance is…

> You must not eat, drink, exercise, or smoke within 30 minutes of a reading. You must have an empty bladder. You must sit straight up in a chair with back support. Your legs must be uncrossed and your feet must be flat on the ground. The arm to be measured must be rested on a flat surface so that it is at the same level as your heart, not lower, not higher. You must sit calmly, without talking for five minutes to relax before the reading. When it's time, an appropriately sized cuff should be wrapped around your bare upper arm, right above the elbow; it should never be wrapped over clothing. At least two readings should be taken, with the average recorded. Ideally, readings should be taken in both arms, with the highest readings recorded.

When was the last time you got it measured properly? Literally never for me in a clinical setting. I don’t know why they bother honestly.

Probably never, I have really long arms and they usually take it just barely above the elbow also. I have always been on the higher end even when in my 20s and training/dieting for athletic events.

Used to flummox me until I bought my own meter, they can be like $30.

And what's the typical variance (from "actual") for a "usual" reading?

Good question, for myself personally (anecdotally) I got systolic of 145-ish in the doctor's office and 120-ish at home. This was validated by a medical take-home 24h cuff.

Doctors recognize that non-invasive BP measurement is an imperfect screening tool. Anybody worth their salt isn't getting worked up about these level of details, because it's largely a waste of time and effort. The solution to an error prone screening tool is not to repeatedly use the screening tool. You move on to more accurate and focused methods of testing.

What's the point of taking your blood pressure if doing any of these things causes significant variance? I'm not meditating at home or out and about all day. So why does it matter what my blood pressure is in one single state? What if I'm in an elevated state all the time? What if I never am? It makes it really hard to believe that blood pressure readings are anything more than nonsense.

If you're doing a double leg press (especially in conjunction with a Valsalva maneuver) you can get an instant BP reading as high as 320/250. If that's your idle BP then you're not long for this world lol.

If your BP - measured in a specific and consistent set of conditions - is elevated vs baseline then you are at an increased risk for a set of medical conditions. Researchers could have picked any set of conditions to establish that baseline but I assume that idle is easier to standardize on than e.g. double leg press with 3 RIR. It's not which condition per se but rather that it's the condition researchers aligned on and studied.

The problem is that if the risk is established based on your deviation from the baseline, then you must be measured in the same conditions under which the baseline was established otherwise the results don't mean much if anything at all.

10-20 mmHg.

https://www.ncbi.nlm.nih.gov/books/NBK482189/

> Smoking within 30 minutes of measurement can raise the systolic blood pressure to 20 mmHg

> a distended bladder can increase systolic and diastolic measurements by 10 to 15 mmHg.

> Sitting in a chair lacking back support can raise systolic blood pressure to 10 mmHg, and a similar increase is observed when both legs are crossed.

> Talking/listening during measurements can increase systolic and diastolic measurements by 10 mmHg.

The major exception is cuff placement over clothing which is noted to vary results by up to 50 mmHg but doing that is stupid anyway and makes you fail medical school.

> The solution to an error prone screening tool is not to repeatedly use the screening tool.

It can be. Repeated in office blood pressure measurements increase sensitivity and lower specificity. It's not as good as 24 hour monitoring but sometimes that's the best you've got.

For me, the first reading is usually higher (by 20-30, even after a long rest period) and subsequent ones get lower and lower as I calm down from the initial worry about whether I will get a high reading or not.

At the doctor's office / hospital I try to tell them this, but they tend not to care. I think they know it varies a lot, they know about psychological effects, but i) they anyway take it much less seriously than overthinkers like me and some fellow HN-ers would imagine and ii) they may prescribe something and anyway expect it not to do much, and also expect the patient not to follow through with taking it properly etc. Honestly, the whole thing is quite a farce. The painful truth is that generic lifestyle improvements are the biggest bang for your buck, instead of worrying about getting exact and precise blood pressure readings.

The other similar big thing is routine blood tests for deficiencies and cholesterol, iron etc. It can also have huge variance over the year, and often people only do it every one or two years and take it as this extremely solid evidence that you need to take this or that medicine. If we were truly serious about this, we would do several tests, separated by weeks, done with different kit manufacturers at different labs etc.

I think the reason for not doing more thorough testing is implicitly admitting that the results aren't really all that actionable and improved precision doesn't really improve treatments because we have no idea what to really do with the results. There are studies showing correlations/causations of certain interventions on specific markers, and those markers are in turn correlated to some outcomes, but often the "evidence-based medicine" doesn't follow the full chain towards the actual outcome.

The other big reason for not measuring more times is the same that a man with a watch knows the time, but a man with two watches is never quite sure about it. In other words, if you got a test and had a result, you can document this and all is fine.

The idea, in theory, is to measure your "minimum" or baseline blood pressure.

That your activities throughout the day add variable amounts to the baseline but never go below it.

It is a very good question though -- some people have activities/jobs/lifestyles where their BP is significantly elevated all the time. So surely you would think that must matter?

> You move on to more accurate and focused methods of testing

Yes, AFTER the imperfect tool gives you something to worry about. So you still need the imperfect tool, which is what I think a lot of people are missing in this conversation.