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DECODE Study Group, on behalf of the European Diabetes Epidemiology Study Group Correspondence to: Dr Knut Borch-Johnsen, Steno
Diabetes Centre, Niels Steensens Vej 2, DK 2820 Gentofte, Denmark
kbjo{at}novo.dk
Objective: To evaluate the impact of the revised
diagnostic criteria for diabetes mellitus adopted by the American
Diabetes Association on prevalence of diabetes and on classification of
patients. For epidemiological purposes the American criteria use a
fasting plasma glucose concentration
Commonly accepted diagnostic criteria for diabetes mellitus were
developed by the National Diabetes Data Group in 19791 and
the World Health Organisation (WHO) in 19802 and updated
in 1985.3 During its annual meeting in 1997, the American
Diabetes Association (ADA) approved new diagnostic criteria for
diabetes mellitus on the basis of recommendations from an expert
committee on the diagnosis and classification of diabetes
mellitus.4 On the basis of data from three different
populations the intention was to identify the fasting blood glucose
concentration that best predicted the risk of developing microvascular
complications.4 The revised criteria are symptoms of
diabetes and a casual plasma glucose concentration For clinical diagnosis the American Diabetes Association recommended
that the diagnosis should be confirmed by a second test, while for
epidemiological studies they recommended the use of fasting plasma
glucose Diabetes mellitus is one of the most common chronic diseases and is a
major contributor to the development of cardiovascular
disease.5 The prevalence of non-insulin dependent diabetes
mellitus has increased dramatically over the past
decades,6 predominantly because of changes in lifestyle,
increasing prevalence of obesity, and ageing of
populations.7 The estimated worldwide number of people
with diabetes is over 100 million, and in Europe the cost of treating
diabetes and its complications has been estimated to be 5.8% of the
total healthcare budget.8
Any change in diagnostic criteria may not only affect the accepted
prevalence of diabetes but may also result in a reclassification of
individuals. Individuals with diabetes according to the WHO criteria
may not be classified as having diabetes according to the new ADA
criteria and vice versa. We evaluated the impact of the new diagnostic
criteria on the prevalence of diabetes and classification of
individuals on the basis of data from epidemiological surveys carried
out in European countries with the standard glucose tolerance test.
Centres in Europe that had performed population based studies or
studies in large representative samples of occupational groups on the
prevalence of diabetes mellitus in adults were invited to participate.
We identified 13 population based studies9-21 and three
studies in occupational groups.22-24 All centres used a
75 g glucose load. Only individuals with both fasting and 2 hour
glucose values or with previously known diabetes were included.
From each centre crude original data on sex, age, height, weight,
status of known diabetes, and fasting and 2 hour blood glucose
concentrations as well as mode of recruitment, number invited, number
participating, exclusion criteria for oral glucose tolerance test, date
of the start and end of survey, time of day of blood sampling, glucose
load, blood specimen used (venous whole blood, venous plasma, capillary
whole blood), and the method of glucose assay were sent to the diabetes
and genetic epidemiology unit of the National Public Health Institute
in Helsinki, Finland. For subjects known to have diabetes, information
was collected on how their diabetes was assessed. Data were analysed
for each centre individually and thereafter a combined analysis was
performed.
To compare the criteria from WHO and ADA we used the recommendations
for epidemiological surveys
3 4
: 2 hour post-load glucose
and fasting values, respectively. As different methods for blood
glucose measurement were used (table 1), glucose data could not be
pooled. All individuals were classified on the basis of fasting venous
plasma glucose concentration as ADA non-diabetic (fasting plasma
glucose <7 mmol/l) or ADA diabetic (fasting plasma glucose
Table 1.
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Abstract
Top
Abstract
Introduction
Subjects and methods
Results
Discussion
References
7.0 mmol/l in contrast with
the current World Health Organisation criteria of 2 hour glucose
concentration
11.1 mmol/l.
Design: Data were collected from 13 populations and
three occupational based studies from eight European countries. All
studies used a 75 g oral glucose tolerance test to measure fasting and
2 hour glucose concentrations.
Subjects: 17 881 men; 8309 women; age range 17-92 years.
Main outcome measures: Classification of diabetes
according to both sets of criteria.
Results: The application of the American criteria on
European populations induced changes in prevalence of diabetes ranging
from a reduction of 4.0% to an increase of 13.2%. A total of 1517 previously undiagnosed individuals had diabetes according to either the
WHO or the American criteria. Among 1044 with diabetes according to
American criteria, only 45% had 2 hour values fulfilling the WHO
criteria. The risk of disagreement of classification decreased with
increasing body mass index (P<0.00001) and increasing age (P<0.0001);
the impact of sex was not significant (P=0.08).
Conclusions: This shift in strategy from using 2 hour
to fasting plasma glucose will cause an increase in the prevalence of
diabetes in some European populations. A high degree of disagreement in
the classification was observed between the two recommendations.
Prospective data are needed to evaluate whether the WHO or the American
criteria best identify individuals at risk of developing microvascular
complications and cardiovascular disease. Wider implementation of
revised diagnostic criteria should await prospective data.
Key messages
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Introduction
Top
Abstract
Introduction
Subjects and methods
Results
Discussion
References
11.1 mmol/l or a
fasting plasma glucose
7.0 mmol/l or 2 hour plasma glucose
11.1 mmol/l during a standard 75 g oral glucose tolerance test (as
previously recommended by the WHO3).
7.0 mmol/l alone. It was stated that this approach would
lead to slightly lower estimates of prevalence of diabetes than the use
of 2 hour glucose according to the WHO criteria.4 The WHO
Study Group gave both fasting and 2 hour glucose criteria for the
diagnosis (fasting
7.8 and 2 hour
11.1 mmol/l), but for
epidemiological and screening purposes they stated that the 2 hour
value could be used alone, a recommendation followed in most
epidemiological studies.
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Subjects and methods
Top
Abstract
Introduction
Subjects and methods
Results
Discussion
References
7.0 mmol/l) and on the basis of the 2 hour value as WHO
non-diabetic (2 hour plasma glucose <11.1 mmol/l) or WHO diabetic (2 hour plasma glucose
11.1 mmol/l). Corresponding cut off points for
venous whole blood were fasting blood glucose <6.1 versus
6.1 mmol/l and 2 hour blood glucose <10.0 versus
10.0 mmol/l,
and for capillary whole blood the cut off points were fasting capillary
glucose <6.1 versus
6.1 mmol/l and 2 hour values <11.1 and
11.1 mmol/.
Table 2 shows the basic characteristics of the 16 study populations. A total of 26 190 individuals were included in the present study (17 881 men). For the analysis of the disagreement in classification between the WHO and ADA criteria only individuals without known diabetes were included.
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All analyses were performed at the National Public Health Institute in Helsinki with SPSS version 7.5.1 for Windows.
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Results |
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Figure 1 shows the prevalence of
diabetes according to the WHO and ADA criteria. Both sets of
criteria included previously diagnosed diabetic individuals as
diabetic, regardless of their glucose concentration. In six studies the
prevalence was lower with the ADA criteria than with the WHO criteria,
while in 10 studies it was higher with the ADA than with the WHO
criteria. The difference in prevalence with these two criteria ranged
from
4.0% to 13.2% and the overall difference was 0.5% (see
table 1).
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Disagreement of classification between criteria for previously
undiagnosed diabetes
A total of 1517 individuals had diabetes
according to either the ADA or the WHO criteria. Among 904 who had
diabetes according to the WHO criteria, 473 (52%) had a fasting plasma
glucose concentration (<7.0 mmol/l) that did not indicate diabetes
(table 3 and figure 2). Among 1044 who had diabetes according to the
ADA criteria, 59% failed to reach the 2 hour glucose diagnostic value
for diabetes (
11.0 mmol/l).
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Factors associated with disagreement of
classification
Table 4 shows the degree of disagreement in the
diagnostic classification between the WHO and the ADA criteria
according to age, sex, and body mass index. No significant difference
was found for sex. Age was significantly associated with the
probability of disagreement. Individuals below age 65 years were more
likely to be diagnosed on the basis of the ADA criteria than on the
basis of the WHO criteria (P<0.0001). Lean individuals were more
likely to have a high post-load glucose values, while overweight and
obese individuals (body mass index
25 kg/m2) were more
likely to have diagnostic fasting plasma glucose values
(P<0.00001).
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Discussion |
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One main reason for revising the diagnostic criteria for diabetes mellitus has been an intention to simplify the diagnosis of the disease, as epidemiological surveys show that 30% to 60% of all diabetic individuals in the community are undiagnosed. 6 25 Even when patients have no symptoms of hyperglycaemia the risk of cardiovascular disease in this group is doubled, and 10-21% will have microvascular complications (retinopathy, nephropathy, or neuropathy) by the time diabetes is diagnosed.25 Early detection of diabetes is preferable as microvascular complications are preventable through strict glycaemic control 26 27 ; the prevalence of modifiable cardiovascular risk factors such as dyslipidaemia and hypertension is high 24 28 ; and early diagnosis and treatment of retinopathy and nephropathy is essential to prevent blindness and end stage renal failure. The American Diabetes Association argues that fasting blood glucose is easier and cheaper to determine than the glucose tolerance test and should therefore replace it for diagnostic purposes. The present study, however, shows that a change in diagnostic procedure is not a simple issue.
Prevalence and classification
Analysing the impact of revising the diagnostic criteria, we found
that the overall change in the prevalence of diabetes was 0.5% but
with substantial variation between the populations studied. Our
estimate is conservative, accounting only for the change in prevalence
related to previously undiagnosed cases and assuming no effect of the
new criteria on known cases of diabetes.
11 mmol/l
and a fasting value of <7.0 mmol/l, the median fasting value was
6.0 mmol/l. Thus, individuals qualifying as diabetic on one criterion
but not on the other are not just borderline cases who almost reach the
diagnostic level.
The probability of the disagreement in classification depended on age
and body mass index. The WHO criteria were more likely to diagnose
diabetes in lean individuals, while the ADA criteria were more likely
to identify middle aged obese individuals. Thus, the disagreement does
not represent a "random reclassification" but a systematic bias
resulting in a change in diabetic phenotype.
Screening and health economy
Screening should rely on a valid test. In diabetes this means that
it should identify individuals with chronic hyperglycaemia and a risk
of developing microvascular and macrovascular complications. Given the
substantial disagreement of classification between the two diagnostic
criteria, the question is whether the risk is more closely associated
with fasting hyperglycaemia, postprandial hyperglycaemia, or both. This
can be answered only by prospective studies. Two of the three studies
of microvascular complications presented by the ADA expert
committee
4 29
were cross sectional while one, in Pima
Indians, was prospective.30 For macrovascular disease the
number of published similar studies is low. The recent analysis of the
Paris prospective study showed that the incidence of fatal coronary
heart disease was related to both fasting and 2 hour plasma glucose,
but the number of events in the blood glucose intervals of interest was
low.24
Conclusion
We have found that revising the diagnostic criteria as proposed by
the American Diabetes Association not only changes the prevalence of
diabetes in the population but also causes a rather dramatic shift of
status of diabetes in individuals. It will have serious consequences
not only to society and for public health but also for individuals, who
will be labelled as diabetic with personal and economical consequences.
On the basis of our findings and the fact that prospective data
answering some of the above mentioned questions are available for
reanalysis, we would like to recommend that changes in the diagnostic
criteria should be undertaken only after analysis of solid prospective
data, data that are available and currently being
prepared.
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Acknowledgments |
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The DECODE study (diabetes epidemiology: collaborative analysis of diagnostic criteria in Europe) was undertaken on the initiative of the European Diabetes Epidemiology Study Group (chairman Knut Borch-Johnsen; vice chairman Andrew Neil; secretary Beverly Balkau).
The secretariat comprised Knut Borch-Johnsen, Steno Diabetes Centre, Gentofte, Denmark; Johan Eriksson, Qing Qiao, Jaakko Tuomilehto, department of epidemiology and health promotion, National Public Health Institute, Helsinki. Data analysis was carried out by Qing Qiao and Beverley Balkau, INSERM U21, Paris, France. The writing committee comprised Knut Borch-Johnsen, Jaakko Tuomilehto, and Beverley Balkau.
Funding: Novo Nordisk, Bagsvaerd, Denmark, supported this analysis by a fellowship for Dr Qing Qiao for data analysis.
Conflict of interest: None.
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References |
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from the West to the rest.
Diabetes Care
1992;
15:
232-252[Medline].
do we need new criteria?
Diabetologia
1997;
40:
247-255[Medline].(Accepted 5 May 1998)
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