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How to Know If You Have High Blood Sugar

high blood sugar

How do you know that you have high blood sugar level?  Let us first understand that Diabetes is not a disease. It is a condition in which, if the level of blood sugar is higher than a certain level, the risk of heart disease, kidney failure, blindness, and even death are substantially high. Of course, even with normal sugar levels there still is 20% risk of these diseases.

The real question is how many grams of sugar per liter of your blood is safe. Various institutions have carried out trials for deciding a cutoff point. Around the mid-1990’s, the American Diabetes Association (ADA) convened an expert committee to re-examine the diagnosis of Diabetes in light of the new information available. They considered the following trials:

  • PIMA Indians trial of 960 individuals.
  • Egyptian trial of 1081 individuals.
  • The Third National Health And Nutrition Examination Survey (NHANES III) of 282 individuals.

The mid cut off point obtained for 2hr OGTT of the above 3 trials were 298mg/dL, 252m/dL and 292mg/dL respectively.

Here, development of retinopathy was taken as a basis to decide the cutoff point above which the patients had substantially higher chances of developing retinopathy.

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Instead of considering the above-mentioned mean value of the bimodal threshold, which is the standard followed in such research analysis, they chose to adopt the lowest glycemic level of each of initial decile in which the prevalence of retinopathy increases which were  244mg/dL, 218mg/dL and 195mg/dL respectively. Even the mean of the 3 values is 219mg/dL but ADA decided to retain the initially proposed value of 2hr OGTT by NDDG i.e. 200mg/dL which is misleading and has great potential of diagnosing a false positive case of Diabetes.

Hence, to arrive at a proper 2hr OGTT threshold, we must consider controlled trial on different populations. Following table shows the cutoff point after 2hr 75gm of oral glucose consumption (OGTT).

PopulationYearPublication2 hr Glucose
Samoa1984Diabetes Research208
Mexican Americans1985Journal of Chronic Diseases231
Kiribati1993Journal of Diabetes and its Complications228
Wanigela1994Medical Journal of Australia268


The above mentioned 2hr glucose cutoff point value is of the population in the age group between 35 years to 50 years. We have to find the mean value of the cutoff point in the above four populations to define a reference point.

208 + 231 + 228 + 268 / 4 = 233.75

233mg/dL is very close to the 2hr OGTT cutoff point arrived by the PIMA Indians trial on 941 individuals i.e. 227mg/dL.

It may be appropriate for us to conclude that for an individual up to 50 years of age the plasma random blood sugar or 2hr Oral Glucose Tolerance Test value for being diagnosed as a diabetic can be > 230mg/dL.

Another factor to consider is that the above results are from blood samples taken from veins whereas at home, normally blood is taken from capillary of the fingertip using a glucometer to measure sugar levels.  It is universally accepted that glucose concentration in the blood taken from the capillary is around 10% higher.

It means you have to add 10% i.e. 23mg/dL to 230mg/dL to arrive at the value of the random blood sugar cutoff point. This means capillary blood sugar level of 230 + 23 = 253mg/dL should be considered as the cutoff point for diabetes (for people up to 50 years of age).

It has been a trend in medical science to round off diagnostic figures to the nearest whole number (as in case of blood pressure and total cholesterol). So we can round off the value of 253mg/dL to 250mg/dL.

This cutoff point of 250mg/dL is of less value if we do not consider other factors. The prominent one being age. Due to evidence-based medicine, science has understood that metabolic activities in the body show a dramatic change with age. Blood sugar and blood pressure are two such metabolic activities °which are influenced by the age factor. So keeping a single cutoff point across a wide spectrum of age is not of use in the real clinical diagnosis. One trial on over 2900 PIMA Indians was conducted to see the effect of age on blood sugar levels, two hours after 75gms of carbohydrate load.

Age GroupNo. of Examined MalesMean 2hr GlucoseNo. of Examined FemalesMean 2hr Glucose
5 - 14 years55099.9mg/dL606104.89mg/dL
15 - 24 years245107.49mg/dL314112.19mg/dL
25 - 34 years139154.49mg/dL186226.29mg/dL
45 - 54 years96208.79mg/dL112256.69mg/dL
55 - 64 years83214.99mg/dL106293.19mg/dL
65 - 74 years81210.09mg/dL52229.49mg/dL


  • A clear increase in blood sugar with age.
  • After the age of 65 years, the blood sugar level tends to drop a bit (same for blood pressure).
  • There is no clear-cut rate of increase of blood sugar in relation to the age.
  • In the 25 to 35 years bracket, there is a trend of steep increase in blood sugar value i.e. more than 40mg/dL.

It would be wise to include age adjustment factor to the value of 250mg/dL 2hr OGTT, so as to avoid detection of false cases of diabetes in individuals above 50 years and false negative cases of diabetes in individuals aged 25 years. Conservatively, on the basis of the observation, we can safely add 1mg/dL for every added year after 50 years.

So for a 60 year old individual, capillary blood sugar after 2 hour of consuming 75gms of glucose should be 250mg/dL + 10mg/dL = 260mg/dL to become a diabetes patient.

A similar approach can be applied to obtain a more practical value of fasting blood sugar and HBA1C.

Here one must consider the fact that the major trials specifically on PIMA Indians were done where the day temperature varied between 18°C to 38°C. So the previous cutoff point is suitable for a place where day temperature is not below 10°C. Hence, the population living in a cold climate must consider temperature change factor.  It has been observed that in winters the blood sugar increases roughly by 10mg/dL. So the figure for a 50-year-old person during winter in capillary blood sugar 2hr PG > 250+10=260mg/dL should be diagnosed as a diabetic patient. We must also check if the person is suffering from viral infection/fever as there is a 10% increase in blood sugar during sickness.

To avoid a false diagnosis of high blood sugar, the final value  of random blood sugar should be adjusted by:

  • Adding Age Adjustment factor.
  • Adding Winter Adjustment factor.
  • Adjustment because of viral infection/fever.
  • If you have eaten recently, the blood sugar level from blood taken from fingertip can be up to 70mg/dL higher than blood taken from a vein.

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Finally, I have to add that there is also a variation of about 10 to 20% between different glucometers. This is how you know if you have high blood sugar.

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Here I have to mention that HBA!C is not an accurate or recommended test.

It is not measuring your blood glucose levels directly. It is giving you a rough estimate of your blood sugar over 3 months. It is actually measuring the percentage of haemoglobin that is bound to glucose.

If you have the low iron enema you will have an abnormally high HBA1C reading which is not accurate. There is another enema in which you will have low HBA1C. In case of live of kidney disease the number is again not going to be accurate.