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Original Article
Journal of Nepal Association for Medical Laboratory Sciences
JNAMLS | VOL. 11 | NO. 1 | DECEMBER, 2012
14
ASSOCIATION OF ESTIMATED AVERAGE GLUCOSE (EAG) WITH
FASTING, POST-PRANDIAL AND AVERAGE OF FASTING AND
PP SERUM GLUCOSE LEVELS
Ram Vinod Mahato1*, Ashwini Kumar Nepal2, Basanta Gelal2, Bibek Poudel3, Binod Kumar Yadav3,
Rajendra KC2,Prabin Gyawali5, Prashant Regmi4, Prakash Atreya6
1 Central College of Technology, Tribhuvan University, Hattishar, Dharan, Nepal, 2Department of Biochemistry, B.P. Koirala Institute of
Health Sciences, Dharan, Nepal, 3Department of Biochemsitry, Manipal College of Medical Sciences, Pokhara, Nepal
4Institute of Medicine, Tribhuwan University Teaching Hospital, Kathmandu, Nepal, 5Clinical Laboratory Services, Dhulikhel Hospital,
Kathmandu University, 6Metro City Hospital, Kathmandu, Nepal
Corresponding author: Ram Vinod Mahato, Lecturer, Central College of Technology,
Tribhuvan University, Hattishar, Dharan, Nepal, Email: vinodmahato@yahoo.com
ABSTRACT
Introduction: Diagnostic criteria of Diabetes mellitus (DM) has been devised by World Health
Organization (WHO), American Diabetes Association (ADA), based on plasma glucose level on
random, fasting and post-prandial (PP) condition. Glycosylated Hemoglobin (HbA1C), once considered
as marker of chronic hyperglycemia, is now advocated for diagnostic criteria for diabetes mellitus. The
calculation of estimated Average Glucose (eAG) from the HbA1C values using Nanthan’s regression
equation is crucial as it helps the patients of diabetes and their health care providers better understand
their glycemic control over the previous 8-12 weeks.
Objectives: To calculate eAG from HbA1C values and study its correlation with fasting, PP, and
average of fasting and PP serum glucose levels.
Materials and Methods: A hospital based cross-sectional study carried out at Kantipur hospital,
Kathmandu from July 2010 to March 2011. A total of 97 diabetic patients were enrolled in this study.
Fasting and PP blood samples were collected in sterile plain vial for estimation of blood glucose and
EDTA vial for estimation of HbA1c, eAG was calculated from HbA1C value using Nathan’s regression
equation (eAG (mg/dl)= 28.7 X HbA1C – 46.7). The results were then interpreted using Statistical
Package for The Social Sciences (SPSS) version 16.0.
Results: A total of 97 diabetic patients (male=70, female=27) were enrolled for the study. The mean±SD
values for HbA1C and the blood glucose parameters were: HbA1C (7.65±1.48), eAG (172.69±41.16), fasting
(126.18±39.45), PP (178.88±59.14) and average of fasting and PP (152.52±46.97). HbA1C values were
signifi cantly correlated with the blood glucose parameters fasting(r=0.61, p<0.001), PP(r=0.65, p<0.001),
average of fasting and PP(r=0.67, p<0.001) and eAG (r=1.00, p<0.001) (Table 2).
Conclusion: eAG values are highly correlated with fasting, PP, and average of fasting and PP blood
glucose values. So, blood glucose expressed as eAG improves the understanding of blood glucose
monitoring.
Key Words: Glycosylated Hemoglobin (HbA1C), estimated Average Glucose (eAG), Diabetes Mellitus,
Diagnostic criteria
Original Article
Journal of Nepal Association for Medical Laboratory Sciences
JNAMLS | VOL. 11 | NO. 1 | DECEMBER, 2012 15
INTRODUCTION
Glycosylated Hemoglobin (HbA1C) is a key
parameter for understanding glycemic control in
diabetes. In general, clinicians understand HbA1C
and its limitations well, but evidence suggests that
patients have diffi culty understanding what HbA1C
means and how it relates to glucose. Therefore
it’s worth to express HbA1C in terms of average
glucose that patients more easily understands.1
Diagnostic criteria of DM has been devised by
WHO, ADA, and International Diabetes Federation
(IDF) based on plasma glucose levels on random,
fasting and post-prandial condition but has been
revised from time to time.2, 3 There are diffi culties
and fl aws in blood glucose estimation and may not
refl ect the true glucose values and the underlying
pathological processes that damages target
organs causing chronic complication. Glycosylated
Hemoglobin (HbA1C) once considered as marker of
chronic hyperglycemia is now offi cially endorsed
for diagnostic criteria for DM by international expert
committee including the ADA, IDF, and European
Association for the Study of Diabetes (EASD).4-6
Glycosylation of hemoglobin is more related to
average glucose level in preceding 3-4 months.
There has been many attempts to correlate
HbA1C level and average glucose preceding the
evaluation of these parameters in the laboratory7-9
This study aimed to determine the HbA1C, estimate
the average glucose (eAG) from HbA1C values and
correlate with the blood glucose obtained during
fasting, post prandial (PP) state and their average
values.
MATERIALS AND METHODS
This hospital-based study was carried out at
Kantipur Hospital, Kathmandu from July 2010
to March 2011. After taking informed verbal and
written consent, 97 diabetic patients (male=70,
female=27) attending the diabetic clinic were
enrolled for the study. Blood samples were
collected in sterile plain vial for estimation of
glucose and EDTA containing vial for estimation
of HbA1C. Glucose was estimated by Glucose
Oxidase-Peroxidase Method (RFCL, India)10 and
HbA1C was estimated by affi nity chromatographic
method (Nyco Card, Axis shield Norway).11 eAG
was calculated from HbA1C value and correlated
with fasting , post prandial glucose level in each
patients.
Calculation:
eAG (mg/dl) = 28.7 X HbA1C – 46.710
Statistical Analysis
Data were entered in MS Excel 2007, then
analyzed using SPSS version 16.0, (SPSS
Inc. USA). Descriptive and inferential statistics
including mean, standard deviation, Student ‘t’
test and Pearson’s correlations test were applied
as statistical tools. A p value of less than 0.05 was
considered to be statistically signifi cant at 95%
confi dence intervals.
RESULTS
A total of 97 diabetic patients (male=70, female=27)
were enrolled for the study. The mean±SD values
for HbA1C and the blood glucose parameters were:
HbA1C (7.65±1.48), eAG (172.69±41.16), fasting
(126.18±39.45), PP (178.88±59.14) and average
of fasting and PP (152.52±46.97). Among the
male and female subjects, there was no signifi cant
difference in the mean±SD values of the blood
glucose parameters HbA1C (p=0.88), eAG (p=0.88),
fasting (p=0.78), PP (p=0.42) and average blood
glucose (p=0.53) (Table 1).
HbA1C values were signifi cantly correlated with
the blood glucose parameters fasting (r=0.61,
p<0.001), PP (r=0.65, p<0.001), average of fasting
and PP (r=0.67, p<0.001), (Table 2). Figure 1
shows the correlation between HbA1C and average,
Post-Prandial and fasting glucose level in all the 98
patients. Fasting, PP and average glucose shows
proportionate distribution but always lower, higher
and random pattern of distribution respectively in
relation to corresponding HbA1C values.
Original Article
Journal of Nepal Association for Medical Laboratory Sciences
JNAMLS | VOL. 11 | NO. 1 | DECEMBER, 2012
16
Table 1: HbA1C and blood glucose parameters eAG, Fasting, PP and average of fasting and PP in
the enrolled subjects
Parameters Male (n=70) Female (n=27) Total (n=97) P value
HbA1C (g/dl) 7.65±1.48 7.61±1.32 7.64±1.43 0.88
eAG (mg/dl) 173.06±42.52 171.73±38.14 172.69±41.16 0.88
Fasting (mg/dl) 125.49±33.40 127.96±52.72 126.18±39.45 0.78
PP (mg/dl) 175.87±56.37 186.67±66.27 178.88±59.14 0.42
Average of fasting and PP (mg/dl) 150.67±42.36 157.31±57.89 152.52±46.97 0.53
Student ‘t’ test was applied to compare the
mean ±SD values of blood glucose parameters
between male and female at 95% confi dence
intervals, considering p value <0.05 as statistically
signifi cant.
Table 2: Correlations of HbA1C with blood glucose parameters fasting, PP, eAG and average blood
glucose
Blood glucose parameters Correlation coeffi cients (r) P value
Fasting 0.61 <0.001
Post prandial (PP) 0.65 <0.001
Average of fasting and PP 0.67 <0.001
Estimated Average Glucose (eAG) 1.00 <0.001
Pearson’s correlation was applied at 95% confi dence interval considering p value <0.05 as statistically
signifi cant.
Figure 1: Scatter plot showing Correlation of Fasting (F), Post Prandial (PP) and their Average (A) with
HbA1C Values
Original Article
Journal of Nepal Association for Medical Laboratory Sciences
JNAMLS | VOL. 11 | NO. 1 | DECEMBER, 2012 17
DISCUSSION
The present study showed signifi cant correlations
between the fasting, PP and average of fasting and
PP with eAG. Among which the average fasting
and PP values were highly correlated, which is
supported by various studies.12 Similarly, a strong
positive correlation between fasting plasma glucose
levels and estimated average blood glucose levels
(r=0.757, p=0.05) was observed in a study by
Bozkaya et al.13 Also a study by Rosediani et al
revealed that both postprandial plasma glucose
(PP) and fasting plasma glucose (FPG) correlated
signifi cantly with HbA1c but PP showed better
correlation with HbA1c than FPG (r= 0.604 vs.
0.575).14 Several physiological and biochemical
factors interplay the roles in maintaining the blood
glucose level and HbA1C within the reference
range. After the entry of glucose to red cell, it tends
to be attached to valine, an amino acid present in
N-terminal end of β-globin chain of hemoglobin,
in the process known as glycosylation. With blood
glucose level in within reference range (70-110
mg/dl), HbA1C also is within the reference range
(4-6%). When glucose level is elevated, as it
happens in case of DM, more glucose enters into
red cell and attached to β-globin chain, hence
HbA1C is elevated. This elevation is proportional to
eAG preceding 3-4 months.15, 16
Usually DM is diagnosed by fasting and post-
prandial glucose level in our settings. Fasting
glucose more than 126 mg/dl and PP more than
200 mg/dl is considered as diagnostic of DM.
But blood glucose refl ects the transient levels
and variation are seen during the days as well as
different laboratory conditions.17, 18 Methodology of
blood glucose estimation varies from laboratory
to laboratory, and values are inconsistent.
Glucose level fl uctuates every hour depending
on the physical, mental and dietary conditions,
and does not represent true glycemic status in a
day.19 Measurement of Glycosylated Hemoglobin
(HbA1C), is rather parameter of interest, to look
into the glycemic control over previous 3-4 months
and should be carried out at least twice a year in a
patient suffering from DM.20 The American Diabetic
Association (ADA) and American Association
of Clinical Chemistry (AACC) recommends that
clinical laboratories report the eAG with HbA1C.4, 21
During the treatment of DM, blood glucose level is
maintained as close as possible to a normal level to
minimizing risk of long term vascular complications.
If glucose level uncontrolled, causes glycosylation
of proteins of vital organs and get damage as a
consequences. High level of blood glucose not
only causes glycation of hemoglobin but also
glycate common protein, in tissues where glucose
entry is independent of insulin like kidney, retina,
lens, neurons etc causing long term complication
of DM through Advances Glycosylation End (AGE)
Products.22, 23 HbA1C circulates in the blood and
by itself is not harmful. Rather this molecule is
considered as marker for prediction of diabetic
complications like nephropathy, retinopathy etc. It
is true that HbA1C shows less biological variation, no
change in acute illness, also no need for overnight
fasting. At present day scenario, diabetologist
are looking for a marker, which remain constant
throughout day and night and is not infl uenced
by minor illness, also acceptable to the patients.
Ideal one fulfi lling these criteria is HbA1C. Though
it is costly affair, still it is advantageous, provided it
should be estimated by reference method, obliging
international guidelines. Reporting of HbA1C value
as eAG will be a defi nite advantage for a treating
physician to convince the patient of importance
of glycemic control and many laboratories report
eAG along with HbA1C.24
CONCLUSION
In conclusion, the importance of HbA1C in diagnosis
and management of DM can be re-emphasized,
because it shows high correlations with fasting,
PP and average blood glucose values. So, HbA1C
along with eAG may be added as the diagnostic
test for DM, for the better understanding to
maintain strict glycemic control.
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