can we roughly compute hba1c from the average of fbs and ppbs

can anybody contradict or support the following view point.?

find the average of the ppbs and fbs ..[ie, the sum devided by two]

consider this as a rough value of estimated average glucose , eag,

and find out an aproximate value of

HbA1c from the chart

the idea is that we can continuously asses the hba1c

[a correction can be given to this value and the correction may become consistent individually, in course of time]

whenever we make the tests.

people are generally blind of their hba1c as it is expensive test.

[or more precisely the average of the

prelunch and 2 hour ppbs[after lunch].

this average will give better results for people having dawn effect and ppbs below fbs.]

this opinion[entirely my personal hypothesis] comes as a reply to mr Patliputra asking me

'is ppbs more correlated to hba1c than fbs?'

what is the use worrying about ppbs or fbs when hba1c is the gold standard for assesing the magnitude of complications of diabetes.?

good luck

21 Replies

  • Average BS not always match with the estimated av. BS by Hba1c.

  • give evidence.

    even if they do not match,

    what is the percentage of mismatch.

    an insignificant less than 5?

  • My av. BS is always in between 110-115. But Hba1c is in range of 5.3-6.1.


  • somewhere in the middle of the article given by you :

    '"Because A1C is based on hemoglobin, both qualitative and quantitative variations in hemoglobin can affect the A1C value. These factors need to be considered when interpreting A1C results and serve to limit the use of A1C as a diagnostic test for diabetes. "

    pitfalls in a1c is not be discussed here.

    you see i have mentioned it in the reply to eddy just few posts below. -the last item.

    his hba1c is much less at 4.9 where he should get something like 6.3 . some troble means-haemoglobin ,liver,kidney.etc

    i tried to correlate the

    average of fbs and ppbs to

    hba1c [with an individually tailored correction factor]

    "These factors need to be considered when interpreting A1C results and serve to limit the use of A1C as a diagnostic test for diabetes. "

    this simply means in some people it can vary and we have to interpret.

    that is a different thing altogether.

    again the percentage of mismatch is not mentioned by you.

    thanks anyway for response.

    good luck

  • your personal average glucose is 112.5=113

    your hba1c average is 5.7

    the chart tells it as 5.6

    this is great correlation only-

    who knows those measurements are so perfect within plus or minus 0.1

    moreover the estimated average is not the glucometer average.

    they will coincide if everything is perfectly random and the measurements are sufficiently large, as in probability theory.

    good luck

  • In my opinion If a person have some infections like wounded or infected nose or fever etc then blood sugar also high more FBS. Then HBA1C is also more it has not accurate ?

    For several years back have tested in lab FBS 145 PPBS 168 HBA1C 5.9

    Before testing 15 days I have suffering my infections caused nose problems and nose swelling afterwards i am suffering from fever for 4 days

    As per Doctors opinion any thing stressed action effects the body and also if a person is diagnoised as diabetic he always diabetic it cannot curable even in normal range his blood is synthetic that is why any fever or infections and any part wounded then it cures verylately than other persons

    I think it effect only that period so HBA1C is also different because HBA!C is average of 12 weeks if 15 days is high BSLremaing period how to calculate? So for normal condition HBA1C is correct .

  • dear nataraj,

    if you do not have any specific problems relating to hemoglobin or liver,kidney etc

    hba1c tells the average glucose for the previous 3 months.

    this will also take into account for the glucose rise for

    period during which someone is sick.sick or non sick it just tells the glucose average.

    i have an anology for this.

    pickled mangoes.

    you put mangoes in a salt solution.

    after a wek,one month or two, you check up how much salt entered the mango?

    you will find the more the time the more salt in the mango

    but this answer is incomplete.

    because the salt that entered the mangoes is dependent on the concentration of the salt solution also.

    in other words glycosilation is dependent on the bs rise as well as how long the rise remains.


    glucose rises to 200, for only 10 minutes for one person.

    but in another one, the rise remains for 20 minutes.

    the second person gets more hba1c.

    hba1c is thus an average indicator.

    this anology falls short in one thing .

    the red cells die in about three months.

    thus we get only an average for three months. so far so good.

    last time i had requested you to write simple sentances so that others can understand you.

    long sentance was the habit in the 19th and early 20th century.

    everybody nowadays in science uses short sentences and simple language.

    good luck

  • Indiacratus HBA1C is tells the average of blood glucose inthe body for previous 3 months In this case the persons not healthy,

    or any sickness if wetake HBA1C test then rsult inculded sickness time valy So HBa1C is accepted when the people in normal healthy time otherwise it as not accurate

  • yes you are right.

    when prolonged sickness or conditions like hemoglobin error or

    liver or kidney dysfunction

    the hba1c has to be understood

    with a consideration.

    the value has to be interpreted accordingly.


    good luck

  • I agree, a very rough estimate can be made from average fbs and ppbs, but as it is said terms and conditions apply.

  • agreed.

    on conditions .ok.

    i will elaborate what i mean by an individually tailored correction number.

    if a person finds his average of fbs and ppbs as 144 ,

    but his measured hba1c is 7 which corresponds to 154 in the chart.

    the correction to 144 is obviously 10 units.what i mean is ,this will remain substantially constant for future measurements.unless the amount of diabetes itself alters in an individual.

    this correction may be different for lunch and dinner.

    what is the great advantage of this average ?

    you need not even remember the hba1c --

    every time just keep in mind the average of fbs and ppbs.


    both ppbs and fbs influence the area under the curve[giving total glycemia]

    in this scheme

    it is unimportant which one influences more.ppbs or fbs .

    one thing to note is ppbs is dependent on the quantity and type of food,

    which every diabetic is supposed to control.

    for eg.

    split meal and go low gi etc.

    both these can reduce the bs rise,

    with constant total dietary carb[glucose] intake.

    this idea of average is purely my considerations only. as such open to criticism .


    good luck

  • y ou can forget the chart also later.

    few numbers only you need to remember.

    in the neighbourhood of the individuals


    hba1c 7 means bs=154

    8 means bs =183

    and the like.

    [7.5 ---gives169 the average of 154 and 183]

  • I feel it may not serve the purpose of accurately arriving at HbA1c,particularly if you are testing with a gluco meter.Better to go for HbA1c test.

  • dear venkatji and patliputraji

    kindly see reply at bottom

  • dear venkatji and patliputraji,

    thanks for the criticism.


    the arrival of hba1c

    we were using only premeal and post meal bs measurements. .

    with such two numbers

    it is difficult to have visualisation of

    the 'complications magnitude'.

    hba1c not only solves this ,

    but also tells for a larger perriod,

    3 months.

    but between two consecutive hba1c measurements

    we are again back in the two number state of affair.

    the mean value of fbs and ppbs[preferably ogtt] can take us back to the single number visualisation.

    how far it will be acurate can only be given by a field study.

    once habituated,

    a person can even forget even the correction number which i had sugested.

    what i mean is:

    a person finds his laboratory value of hba1c is say,7 .

    from the chart he finds 154 as the estimated average.

    his average of fbs of ogtt is ,say 144.

    then the correction number is 10.

    next time he finds the average of fbs and ogtt is say 150.

    now he adds 10 to 150 and gets 160 .

    from the chart he finds the corresponding hba1c as 7.2 for 160

    which tells that the expected next hba1c will be 7.2.

    his diabetes has 0.2 percent in terms of hba1c.

    .i will not go into an analysis of this further

    but simply give the considerations i had in mind when i made this hypothesis.

    1]it is not based on any facts observed.

    purely mathematical considerations.

    in a graphical situation if the rise and fall can be repeated cyclically

    then there will be a point in the graph

    which can represent the average.

    [or the average =from the area under the curve, for those who are conversant with the concept AUC]

    there may be more than one point but the one that can repeat consistantly has to be singled out like fbs and ppbs-of ogtt 2 hr.


    when an effect is dependent on two numbers it is practice in mathematics to take a mean, or geometric mean, or form a qudratic sum and find the rms etc]]

    2] the WHO gives a technique of superimposition when they say if a person has three or more values above the healthy mans glucose values

    the person [the person under study ]is diabetic.

    3]every 1 percent of rise in hba1c corresponds to rise of 29 units of estimated bs, which clearly tells a linear relation.

    4] ppbs rises over a pedastal of fbs.

    5]one can visualise the total area AUC as the sum of two numbers

    1)fbs multiplied by 24 and

    2)ppbs minus fbs multiplied by some 16

    [ ppbs as conceived as the sum of fbs and an excess value due to dietary glucose.]

    .[16 hours of food and dietary glucose playing the role]


    1)fbs multiplied by some 8 hrs or so .

    2)and ppbs multiplied by 16 hrs.

    we imagine we are with out food for 8 hours and fbs is the only bs value in a basal style.

    and when food comes ,ppbs remains for 16 hours till the digestion of the dinner is complete say at around 12 midnight..

    thanks for patient reading.

    good luck

  • There was no criticism. Fbs and ppbs does give a very rough estimation of HBA1C, but it does not take into consideration of spikes and falls in bs through out out day and night. Daily estimation of A1C is not of much importance.

  • thanks mr patliputra,

    it was due to my predisposition in philosophy circles ,where

    critique means simpliy an analysis.

    in modern english, of course a criticism is something disaproving.

    probably the most quoted book by Immanuel Kant

    is titled 'critique of pure reason'-----

    "Usage Note: Critique has been used as a verb meaning "to review or discuss critically" since the 18th century, but lately this usage has gained much wider currency, in part because the verb criticize, once NEUTRAL between praise and censure, is now mainly used in a negative sense."

    praise or disaproval i am always thankful to you.

    your voice is that of sanity and dispssionate understanding.

    good luck

  • I am not a dictionary man, though I may be interested in philosophy,based on my own experience and interpretations. And that may not be in line with the main stream thinking.

  • agreed

  • No... HbA1c refers to glycated haemoglobin - is the average blood sugar levels have been over a period of weeks/months.

  • kindly see my explanation above in this page giving "but between two consecutive hba1c measurements

    we are again back in the two number state of affair.



    the arrival of hba1c

    we were using only premeal and post meal bs measurements. .

    with such two numbers

    it is difficult to have visualisation of

    the 'complications magnitude'.

    hba1c not only solves this ,

    but also tells for a larger perriod,

    3 months.

    but between two consecutive hba1c measurements

    we are again back in the two number state of affair.


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