Logic behind taking samples for post-prandial test 1.5-2 hours after food

I am taking NovoRapid and Levemir insulins in a basal-bolus regimen. The NovoRapid insulin acts for 4 hours approximately and if the blood sugar levels were normal after 1.5-2 hours after eating won’t I be heading towards a severe low considering the quantity of insulin left to act - almost 50%? So what is the logic behind taking samples for post-prandial test 1.5-2 hours after eating?

I have always aimed for my blood sugar levels to be normal after 4 hours when the bolus insulin is used up and my HbA1C is 7%. Don’t know what this is all about. Any thoughts on this?

  1. Strive to get your A1c closer to 6 if you can do it safely, to avoid complications. I’m not keen on having an A1c near 7.

  2. The “logic” of testing around 2 hours is to see the peak-bg number (typically). If you reduce carbs you can reduce bolus and that is the best way to prevent a post meal low,if you want to have better 2 hour results without going low by 4 hours. Eating too many carbs means taking more insulin, and that is problematic, to say the least when it comes to safe, more level bgs.

  3. If your rapid insulin is much beyond a 50/50 split with your long acting, it indicates you may be eating too many carbs. What is your rapid/long acting ratio? If you fast for a meal or two, are your bg’s remaining level and within your target range?

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Thanks for the useful insights @phoenixbound

  1. I would love to be able to bring down my A1c further down, closer to 6% but I have to figure out how to do it safely since carb-rich foods form the staple vegetarian diet here in India and I have grown up on such a diet

  2. I never knew till now that testing around 2 hours after eating is to see the peak blood sugar levels and knowing that gives me a new perspective to see things.

  3. Nowadays, my bolus-basal dosage ratio is 34:32 (approx. 6% more rapid insulin) on routine days and I am trying to bring down the rapid insulin by a couple of units or more. It was worse before. I haven’t been able to fast for a meal or two ever since I had DKA 3 years back due to foolishly fasting for a day in protest and that lead to a series of problems with digestion, acidity - low and high. But other than that I have tested my blood sugar levels when the rapid insulin is no longer acting and the fluctuations have usually remained within the -30 to +30 range. So I am guessing my basal insulin dosage is close to the needs of my body.

Your goals and logic regarding normal blood sugars after 4 hours are basically sound.

The idea behind a test @ 2 hours after eating is to provide a gauge on how well you bolused (and possible how well you are digesting the food) for the meal. With a 4 - 6 hour activity, NovoRapid has a peak activity of something in the 30 - 45 minute range, so @ 120 minutes, there is not 50% remaining, but more 20 - 25%. I would still agree with you that if you started a meal @ 5.5mmol (100mg/dl) and tested two hours later @ the same level, you will be headed for a low. That is part of the purpose of the test, then. If you are @ normal level two hours after eating, you probably need to eat additional fast acting carbs to prevent a low. Similarly, if you are 11.1mmol (200mg/dl) at two hours after eating, you might want to consider a correction bolus, because the remaining NovoRapid is unlikely to get you to normal in 4 hours.

By checking two hours and four hours after your meals you might be able to spend more time “in range”. Avoiding lows and long periods of highs - IOW, increasing time in range, will likely result in a lower A1C.

Here is a link to the “Mechanism of Action” for NovoRapid.

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