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Relationship between FBS, PPBS, HbA1c

Hello experts,

I want to understand relationship between FBS, PPBS, HbA1c. I have some understanding of them, but want to check with others so that I am clear. Below is my understanding -

FBS - Serum Blood Glucose Level during fasting for atleast 10 Hrs

PPBS - Serum Blood Glucose Level after 2 Hrs after eating food (after fasting for atleast 10 Hrs)

HbA1c - Measure of % of how many RBCs having glucose attached to them.

I believe HbA1c value gives average BS level over last 60-120 days (this is because RBCs live for maximum 120 days and after their death, their glycocelated heamoglobin will be broken down and it will not count for ovrall HbA1c levels)

My question is that my latest 2 readings were as below -

Dec 2014 : HbA1c - 6.9

May 2015 : FBS - 90+, PPBS - 120+, HbA1c - 6.4

Aug 2015 : FBS - 96, PPBS - 121, HbA1c - 5.5

Please note that these 2 readings are from different labs.

How on earth my A1c value reduced from 6.4 to 5.5 in just 2.5 months? I am on the same diet and lifestyle from Dec 2014 to Aug 2015. Do last readings seem to be wrong (problem with the lab)??

Please put your valuable opinions on this. Anyway I will get the tests done in the previous lab next month as I have personal constraint to go to that lab (its in far location) this month.

7 Replies

Firstly,no experts here.Only diabetics like you sharing their personal experiences and knowledge and trying to more insights into this strange disorder called diabetes.In that

sense all are learners only.

If the A1c reading comes down sharply,it might be natural.What we can do is think deeply about it and understand how it has come down.Only you can do it.As far as the lab is concerned,no body can say whether it was right or wrong.One thing you can do is,to see if it is accredited to any established to any reputed institution.I was visiting a lab accredited to CMC Hospital,Vellore,TN.Now,my hospital is accredited to National Board for accreditation of Hospitals ans Health services and WHO.So,I am reasonably sure of the services.

Lastly,make sure the number does not go up.


Thanks venkataramana for your reply.. Latest HbA1c test was done by a diabetes research organization. The test center - Quest Diagnostics. It looks to be a good diagnostics. But still I am not able to understand the drop of almost 1.0 of A1c levels with same lifestyle.


it is possible dont worry quest is very gud lab


Thanks for the reply gkrambati143..


Thanks Anup for your reply.. You have very good knowledge on this.. Can you please elaborate the point - "First months RBC contribute to 50% impact on A1C and by 47th day this number shoots up to as high as over 90%." I am not able to understand it..


Thanks Anup for the reply.. I follow 'moderate' LCHF diet.. not extreme like you.. But planning to switch for full LCHF.. I have been in this diet from Dec 2014.. So I got this doubt whether reading of 5.5 is correct..


What I understand is that PPBS is relied upon only to ascertain how well you are responding to medication to bring down sugar levels. Effective your medication, lower PPBS. HBa1C vascillates depending upon your long term diet over last 3 months. What I have observed is during fruits season my HBa1C naturally is higher. Cant resist mangoes and jack fruit you see :-)

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