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When Is The Best Time To Take A Blood Glucose Reading?

When Is The Best Time To Take A Blood Glucose Reading?

For several years I have been taking blood glucose readings twice a day with what I thought were the instructions. I just had a consultation with my diabetes nurse and discovered that I was using the wrong instructions. 😥

I was taking the PM reading at least 2 hours after the last meal and the AM reading at least 12 hours after the last meal. I was starting the timer at the end of a meal.

What she said now was that there are only 2 types of readings that matter. The post-prandial reading is… read more

A DiabetesTeam Member said:

Let me just put it another way that may make it simpler to understand.

Clinical decisions are made on constants, not variables.

They want a constant measurement between preprandial and postprandial.

So by taking the PPG at 2 hours after the first bite that BG measurement is "constant" - always at a 2 hour interval between pre and postprandial "regardless of the variables".

If you measure at 2 hours after the last bite then how are they supposed to account for the possibly "thousands of variable time frames".

Is the time between actual preprandial and postprandial 2 hours and 5 minutes because you ate fast, 2 hours and 20 minutes or 4 hours?

To many variables.

So even though I agree with what you are saying that the (number) at two hours after the first bite may not capture a very specific meals effect, that doesn't matter because at 2 hours "after the last bite" there is no way to know what the (modified) preprandial was 2 hours before that last bite - and they (believe) that it was at a "measured" preprandial level - not some elevated point from what you have already metabolized.

If your preprandial on a "long meal" was say 95. You start eating. It rises to 140 at 2 hours, you don't test because it's a long meal, you consume a number of more carbs over the next hour and start your timer to test 2 hours later.

So now you were at 140 when you started "adding more sugar". Say that takes you up to 180 by the time you test.

The Doc/Nurse looks at your number as say "whoa" you went from 95 to 180 in 2 hours - we need to put you on 30 units of fast acting insulin. They do this because they believe that's where you were 2 hours "after the first bite" not 5 1/2 hours after eating a long meal.

So you dial it up and end up giving yourself a hypo at 2 hours after you start to eat next time because you don't need to deal with a 180 but really only a 140.

edited, originally posted about 1 year ago
A DiabetesTeam Member said:

It's all about capturing a level at a standardized time.

Let's say you ate 3 cups of mashed potato during your first course in the first 15 minutes of a 2 1/2 hour dinner but waited until 4 1/2 hours after eating that potato to take your reading. It wouldn't be "captured", and then you continue eating with your blood sugar "riding the wave" from those carbs when you ate your desert.

So if you waited until 2 hours after you finish desert you would not be comparing your postprandial to a "realistic" preprandial, you would be comparing it to a "significantly jacked up level" since you would be "barely off the peak sugar level" from what you first ate 2 1/2 hours before. That would have the potential of showing a significantly elevated "meaningless number".

If (they) are trying to figure out how to "dose you" pre-meal "on average" they will figure a dose that will "hit" when your sugars should be peaking without "overdosing" you.

So they need to know "when and how high you are peaking" and that will follow your first bite not the last. The idea is to "treat in real time" not after the fact.

You want to be knocking down the sugars as they are "trying to rise", not wait until they are at max and then start dealing with them.

If the nurse had have explained "why" they were looking for those particular numbers it would probably make more sense.

edited, originally posted about 1 year ago
A DiabetesTeam Member said:

Postprandial, or after meal blood sugars are measured at 2 hours "after your first bite of food".

This is standardized so that the number has some meaning. Your blood sugar may rise very quickly if you eat simple sugars or starches within minutes of them hitting your digestive system. Other more complex carbs can take well over an hour to metabolize and while protein has little effect and fat even less than protein, both will provide a very minimal rise over a period that can extend four hours.

So at (some point) the experts got together and decided to standardize it at 2 hours "after the first bite" and all the guidance is based on that time span even though your numbers are "likely higher" at one hour after starting to eat.

That way it doesn't matter how quickly or slowly you eat or what you eat. It captures a (number) which is used for clinical purposes and over time it will all average out anyhow. Sometimes you will eat quickly, sometimes it will take over an hour, sometimes you will eat fast metabolizing carbs and sometimes none.

At 4 hours after your first bite you "should be" back to your pre-meal level so yes, it could be looked at as a preprandial number "prior to your next meal".

Now, depending on what the Nurse is (looking for) your fasting number may not be important "to her".

Almost nothing you do eating or exercise wise makes much difference to your fasting sugars (although many people blame eating late etc) but that is not the case.

Additionally, your fasting sugars have almost nothing to do with your A1C unless it is the highest numbers you see all day.

It (FBS) is important to figure out dosage recommendations for metformin or basil insulin, but if the clinician is trying to figure out meds to better metabolize "the way you eat" (particularly if they are trying to figure "how many units" of fast acting insulin or a Sulfonylurea dose pre-meal), then FBS is of "no value".

If they really want to figure out "what is going on with a meal" then they will conduct whats called an Oral Glucose Tolerance Test (OGTT). They measure your preprandial level, you consume a liquid with 50 or 75 grams of carbs and then they test at 1, 2 and 4 hours to see "where you were, how quickly you spike, where you are at the "standard test time" and if you return to where you were before you started.

This used to be a "standard test" before they started relying heavily on A1C for clinical decisions.

I personally test my FBS and most carb intense postprandial. But I am not on any meds and according to the guidelines have "no reason to test at all". But I "want to know" when it's getting close to time to start meds and I use my PPG to gauge portion size/safe foods.

edited, originally posted about 1 year ago
A DiabetesTeam Member said:

Usually most doctors want the fasting blood sugar in the morning and a sugar level after 2 hrs after the first bite you eat on your highest Carbs meal (bigest meal of the day). The digestive process starts in your mouth when you chew. Your salivary glands make saliva, a digestive juice, which moistens food so it moves more easily through your esophagus into your stomach. Saliva also has an enzyme that begins to break down starches in your food. (Taken from this site https://www.niddk.nih.gov/health-information/di...).

edited, originally posted about 1 year ago
A DiabetesTeam Member said:

Hhhmmm yes but those kind of meals at restaurants do not happen very often, usually at home meals are eaten within 15 min to 1 hr depending on the food. I am sure they did not mean to test on odd days, unless you are eating restaurant food everyday and followed by a desert, then that might be a different story all together.

posted about 1 year ago
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