How are normal values of blood pressure and glucose determined?

[mktsgm]

TL;DR Summary

How the standard/normal values of blood glucose and blood pressure are determined? what is its history?

Blood glucose is measured and compared against a set of standard/normal values (like, fasting 100 mg/dL etc) to determine if a person has hyperglycemia or not. Similarly Blood pressure readings (systolic & diastolic) are also compared against another set of standard/normal values like 120/80.

My question is, how these standard/normal figures were arrived at? Are they average of some healthy individuals' results or have they been a result of some laboratory tests? What is the methodology adopted to determine those standard/normal values?

I would like to know about its history of these changes also.

Thank you.

 

[.Scott]

As a fellow consumer of blood tests, let me take a shot at this:

Every blood test has its own history - based largely on research studies specific to it. The most common blood tests are used to alert the doctor and patient to the most common medical conditions. Conditions related to obesity are especially well-researched because obesity is so widespread.

For the specific values you are looking at (blood pressure and glucose level), research has correlated different levels with mortality and morbidity rates. Patients are encouraged to stay within these ranges for the potential of a more comfortable and lengthy life. If you follow the advice, your are "playing the odds".

Looking at blood levels more broadly:
1) Initially, a blood/plasma/serum component is identified that has potential diagnostic value.
2) Research may then identify a correlation between some abnormal levels of that component and one or more diseases. If the correlation is strong enough and can be tied to specific treatment decision thresholds, the measurement has diagnostic value.
3) Each blood testing laboratory determines how it's measurement supplies and methods measure certain levels of the component that are important for this kind of diagnosis. These reference levels are provided with the blood level measurements in their reports.

Lab Reference Value Explained.Be sure to see the "questions" at the bottom of that site. For example, if you click on "What are decision limits, you will get:

What are decision limits?

For a small number of tests, long-term studies of certain disease processes have led to the establishment of decision limits that are more useful than reference ranges in determining clinical outcomes and guiding treatment decisions. Decision limits are values that represent either the upper or lower quantity of an analyte that are consistent with a disease state or indicate a need for treatment.
Blood glucose is an example of an analyte for which decision limits have been established and are widely used by healthcare providers. For adults in a routine setting in which fasting blood glucose testing is done to detect type 2 diabetes, a fasting glucose level of 126 mg/dL (7.0 mmol/L) or above, obtained on more than one testing occasion, indicates diabetes. Treatment is required to reduce the risk for cardiovascular disease, kidney disease, and other long-term complications of diabetes.
In this situation, it is a value above a particular limit that provides information rather than a value that falls within or outside a set range of numbers.

 

[phyzguy]

In terms of blood pressure, this site has a nice explanation of how the normal levels were arrived at and why they were changed.

 

[Laroxe]

I think like a lot of physiological measures neither of these represent a standard figure so generally people look at whether the measures you get fall within a particular range of values. These values are often arrived at by looking at the distribution seen in the wider population and evidence about values that impair functioning. Its this second variable that has tended to change over time as we become more aware of the health effects of some of the values particularly the higher values.
Unfortunately like so many things, there are no black and white answers to what is normal or best, for example with blood pressure for a number of reasons the levels tend to rise with age, at least some of these reasons are functional. As arteries age they tend to become stiff and may narrow, so the pressure increases to maintain the blood supply to our brain & kidneys, unfortunately this increase in pressure increases the rate of wear and tear on our arteries and increases the damage. So the guidelines have changed over time, Drs try to keep a persons blood pressure at a low level so they use drugs not to treat high blood pressure as such, they are to prevent the adverse effects that occur over time.
Both of these things were recognised well before accurate measures were available, medics in ancient Greece would taste a patients urine to detect high blood sugar and look for external indicators of high blood pressure like distended arteries.

 

[DrClaude]

In terms of blood pressure, this site has a nice explanation of how the normal levels were arrived at and why they were changed.

Interesting. It shows how the normal is defined not necessarily based on the actual normal, but rather on public health grounds. In my part of the world, 140/90 is still the threshold for high blood pressure.

 

[mktsgm]

Thanks for all those who responded.

Actually, I didn't have any idea about how it is calculated. I wanted to understand the history behind it also. But now I have a little idea.

I had a nagging opinion about however these normal values be calculated, how they could be relevant to all kinds of people all over the world! The physical, mental, and genetic makeup of different people are very different.

After reading the information from the above help, I think instead of depending on ADA/AHA's analysis and numbers, each country should have its own analysis and set of normal numbers.

Not sure, if this insight is OK?

Thanks anyway.

 

[FactChecker]

I think that one way or another, the definition of "high blood pressure" is a balancing act between the dangers of the blood pressure versus the danger of the medicine available to reduce it. So the level will change if new medications are discovered. The level is used to decide whether to take action with available medication. For that reason I would not expect the levels to be much different between countries.

 

[.Scott]

I had a nagging opinion about however these normal values be calculated, how they could be relevant to all kinds of people all over the world! The physical, mental, and genetic makeup of different people are very different.

Certainly these standards would be less relevant in a country such as Chad where the life expectancy is only 55 years.

The glucose levels are tied very tightly to the toxic effects of glucose levels - so if your HbA1C is 7.0, your "physical, mental, and genetic" makeup isn't going to help you without getting that number back down.

For BP, the only reasons related to your community that you would not want to keep your BP below 120/80 might be economic or brief life expectancy. Since many of these BP studies are done in well-fed (or over-fed) and under-exercised communities, I could imagine that there could be reasons for keeping them even lower that are not evident in those groups.