Poor agreement in questionnaire‐based diagnostic criteria ...
New diagnostic criteria and classification of diabetes—again?
2
EDITORIALS New Diagnostic Criteria and Classification of Diabetes—Again? At the end of the 1970s confusion reigned both with regard to the classification of diabetes and to the appropriate diagnostic test. There was enormous variation in diagnostic cut-off values both for the fasting glucose level and after oral glucose loading. The size of the glucose load varied between 50 g and 100 g or was body weight related. Similarly the types of diabetes were loosely divided into ‘juvenile onset’ and ‘maturity onset’, with secondary diabetes, chemical diabetes, borderline diabetes and prediabetes all used in ill-defined ways. In 1979 and 1980 the National Diabetes Data Group (NDDG) in the USA 1 and the World Health Organization (WHO) Second Expert Committee on Diabetes 2 made valiant efforts to create order out of chaos. Types 1 and 2 diabetes, Impaired Glucose Tolerance, Gestational Diabetes and ‘other types’ took centre stage whilst the 75 g oral glucose tolerance test (OGTT) became the gold standard with fasting and 2-hour values defined. There were nonetheless some differences between WHO and NDDG which were resolved in part by a further WHO report in 1985 3 when Malnutrition Related Diabetes Mellitus (MRDM) was added as a major category. There has been a growing feeling over the intervening period that further revision was necessary. Whilst dis- cussions were taking place at WHO, independently the American Diabetes Association established an Expert Committee to re-examine diagnostic criteria and classi- fication. It was felt, in particular, that with the burgeoning of pathophysiological knowledge about diabetes, a more aetiology-based system could be used. The WHO Consul- tation which took place in late 1996 was additionally charged with the more daunting task of making rec- ommendations about the diagnosis and classification of diabetic complications. The ADA Expert Committee reported in 1997 4 whilst Part I of the WHO Consultation appears in the current issue as a consultation document. 5 There was cross- representation between the groups which has certainly helped achieve some consistency in the recommen- dations. A new fasting plasma glucose level of 7.0 mmol l -1 or above is suggested for the diagnosis of diabetes compared with the previous 7.8 mmol l -1 . This is based both on equivalence with the 2-hour value of 11.1 mmol l -1 and on predictive power for microvascular complications, albeit in cross-sectional studies. So far so good! The ADA, however, makes a strong recommen- dation that the fasting plasma glucose (FPG) can be used on its own and that in general the OGTT need not be used. The WHO Consultation by contrast argues strongly for the retention of the OGTT and suggests using the 535 CCC 0742–3071/98/070535–02$17.50 1998 John Wiley & Sons, Ltd. DIABETIC MEDICINE, 1998; 15: 535–536 FPG alone when circumstances prevent performance of the OGTT. The ADA recommendation has already generated considerable steam. It has been shown: (1) that different individuals may be classed as having diabetes using the FPG versus the 2-hour values; and (2) that more people may have diabetes in toto using the ADA FPG test than the 2-hour WHO test. This change of classification is shown in the communications of Kerr et al. 6 and Unwin et al. 7 also in the present issue. Several points should be made. First both ADA and WHO state that in asymptomatic subjects the diagnosis of diabetes can be made only on the basis of at least two abnormal results. The recommendation for clinical classification by WHO has been and remains the 2-hour OGTT measuring both the fasting and the 2-hour values. Only for epidemiological studies does WHO recommend using a single test—2 hours post-glucose load or fasting. Few, if any, of the papers published so far criticising ADA (and by implication WHO) meet the requirements for diagnosis of the individual. In terms of populations the new criteria make sense—it does not matter whether individuals change category as it is the total prevalence that matters. Kerr et al. 6 in this issue indeed make the mistake of referring to only the 2-hour value in classification, and their 4 subjects called IGT by WHO criteria in fact have diabetes according to both ADA and WHO. Other arguments continue about the fasting versus the 2-hour value. It is claimed that people may not be fasting properly and certainly this can be the case. Equally, particularly in developing countries, subjects will not necessarily have had adequate carbohydrate intake beforehand and a ‘diabetic’ 2-hour value may result from undernutrition rather than reflect true diabetes. There has also been discussion about the measurement of glycated haemoglobin as a diagnostic test. Wiener and Roberts 8 in the present issue show that it has high specificity but low sensitivity and suggest it could be used as an initial screen. This may be useful in rich countries, but until the test becomes better standardised and much cheaper it is unlikely to be of use in much of the world. The classification is perhaps less controversial. We now have Type 1 and Type 2 diabetes again, moving away from the clinically confusing terms of IDDM and NIDDM. Type 1 refers to the beta cell destructive process found in the usual Northern autoimmune diabetes, but also to the non-autoimmune type found in some non- Europid populations. Impaired Glucose Tolerance (IGT)
Transcript of New diagnostic criteria and classification of diabetes—again?
EDITORIALS
New Diagnostic Criteria andClassification of Diabetes—Again?
At the end of the 1970s confusion reigned both withregard to the classification of diabetes and to theappropriate diagnostic test. There was enormous variationin diagnostic cut-off values both for the fasting glucoselevel and after oral glucose loading. The size of theglucose load varied between 50 g and 100 g or wasbody weight related. Similarly the types of diabetes wereloosely divided into ‘juvenile onset’ and ‘maturity onset’,with secondary diabetes, chemical diabetes, borderlinediabetes and prediabetes all used in ill-defined ways. In1979 and 1980 the National Diabetes Data Group(NDDG) in the USA1 and the World Health Organization(WHO) Second Expert Committee on Diabetes2 madevaliant efforts to create order out of chaos. Types 1 and2 diabetes, Impaired Glucose Tolerance, GestationalDiabetes and ‘other types’ took centre stage whilst the75 g oral glucose tolerance test (OGTT) became the goldstandard with fasting and 2-hour values defined. Therewere nonetheless some differences between WHO andNDDG which were resolved in part by a further WHOreport in 19853 when Malnutrition Related DiabetesMellitus (MRDM) was added as a major category.
There has been a growing feeling over the interveningperiod that further revision was necessary. Whilst dis-cussions were taking place at WHO, independently theAmerican Diabetes Association established an ExpertCommittee to re-examine diagnostic criteria and classi-fication. It was felt, in particular, that with the burgeoningof pathophysiological knowledge about diabetes, a moreaetiology-based system could be used. The WHO Consul-tation which took place in late 1996 was additionallycharged with the more daunting task of making rec-ommendations about the diagnosis and classification ofdiabetic complications.
The ADA Expert Committee reported in 19974 whilstPart I of the WHO Consultation appears in the currentissue as a consultation document.5 There was cross-representation between the groups which has certainlyhelped achieve some consistency in the recommen-dations. A new fasting plasma glucose level of7.0 mmol l−1 or above is suggested for the diagnosis ofdiabetes compared with the previous 7.8 mmol l−1. Thisis based both on equivalence with the 2-hour value of11.1 mmol l−1 and on predictive power for microvascularcomplications, albeit in cross-sectional studies. So far sogood! The ADA, however, makes a strong recommen-dation that the fasting plasma glucose (FPG) can be usedon its own and that in general the OGTT need not beused. The WHO Consultation by contrast argues stronglyfor the retention of the OGTT and suggests using the
535CCC 0742–3071/98/070535–02$17.50 1998 John Wiley & Sons, Ltd. DIABETIC MEDICINE, 1998; 15: 535–536
FPG alone when circumstances prevent performance ofthe OGTT.
The ADA recommendation has already generatedconsiderable steam. It has been shown: (1) that differentindividuals may be classed as having diabetes using theFPG versus the 2-hour values; and (2) that more peoplemay have diabetes in toto using the ADA FPG test thanthe 2-hour WHO test. This change of classification isshown in the communications of Kerr et al.6 and Unwinet al.7 also in the present issue.
Several points should be made. First both ADA andWHO state that in asymptomatic subjects the diagnosisof diabetes can be made only on the basis of at leasttwo abnormal results. The recommendation for clinicalclassification by WHO has been and remains the 2-hourOGTT measuring both the fasting and the 2-hour values.Only for epidemiological studies does WHO recommendusing a single test—2 hours post-glucose load or fasting.Few, if any, of the papers published so far criticisingADA (and by implication WHO) meet the requirementsfor diagnosis of the individual. In terms of populationsthe new criteria make sense—it does not matter whetherindividuals change category as it is the total prevalencethat matters. Kerr et al.6 in this issue indeed makethe mistake of referring to only the 2-hour value inclassification, and their 4 subjects called IGT by WHOcriteria in fact have diabetes according to both ADA andWHO. Other arguments continue about the fasting versusthe 2-hour value.
It is claimed that people may not be fasting properlyand certainly this can be the case. Equally, particularlyin developing countries, subjects will not necessarilyhave had adequate carbohydrate intake beforehand anda ‘diabetic’ 2-hour value may result from undernutritionrather than reflect true diabetes.
There has also been discussion about the measurementof glycated haemoglobin as a diagnostic test. Wienerand Roberts8 in the present issue show that it has highspecificity but low sensitivity and suggest it could beused as an initial screen. This may be useful in richcountries, but until the test becomes better standardisedand much cheaper it is unlikely to be of use in muchof the world.
The classification is perhaps less controversial. Wenow have Type 1 and Type 2 diabetes again, movingaway from the clinically confusing terms of IDDM andNIDDM. Type 1 refers to the beta cell destructive processfound in the usual Northern autoimmune diabetes, butalso to the non-autoimmune type found in some non-Europid populations. Impaired Glucose Tolerance (IGT)
EDITORIALSis relegated to a risk category and is joined by ImpairedFasting Glycaemia (IFG; Impaired Fasting Glucose in theADA version). Other Types include all those whereaetiology is more clear, such as the MODYs and theformer fibrocalculous pancreatic diabetes variant ofMRDM. One major difference remains in GestationalDiabetes Mellitus (GDM). ADA has stuck to its historictesting and criteria whilst WHO includes both IGT andnew diabetes in pregnancy under the banner of GDM.
Obviously criticisms are possible of both ADA andWHO. We would like to hear preferably constructivecriticisms about the WHO Consultations’ proposalsbefore establishing a final version. Thereafter we hopethat prospective studies will prevail. We stress that thewhole purpose of revising the diagnostic criteria is tohelp establish those at risk of the specific diabeticcomplications so that preventive measures can be insti-tuted as soon as possible.
K.G.M.M Alberti*1, P.Z. Zimmet2
1Human Diabetes and Metabolism Research Centre,University of Newcastle, UK
2International Diabetes Institute, Melbourne, Australia
*Correspondence to: Professor KGMM Alberti, Department of Medicine,The Medical School, Framlington Place, Newcastle upon Tyne NE24HH, UK
536 EDITORIALS
1998 John Wiley & Sons, Ltd. Diabet. Med. 15: 535–536 (1998)
References
1. National Diabetes Data Group. Classification and diagnosisof diabetes mellitus and other categories of glucoseintolerance. Diabetes 1979; 28: 1039–1057.
2. WHO Expert Committee on Diabetes Mellitus. SecondReport. Geneva: WHO, 1980. Technical Report Series 646.
3. World Health Organization. Diabetes Mellitus: Report ofa WHO Study Group. Geneva: WHO, 1985. TechnicalReport Series 727.
4. The Expert Committee on the Diagnosis and Classificationof Diabetes Mellitus. Report of the Expert Committee onthe diagnosis and classification of diabetes mellitus. Dia-betes Care 1997; 20: 1183–1197.
5. Alberti KGMM, Zimmet PZ for the WHO Consultation.Definition, diagnosis and classification of diabetes mellitusand its complications. Part 1: diagnosis and classificationof diabetes mellitus. Provisional report of a WHO Consul-tation. Diabet Med 1998; 15: 539–553.
6. Kerr D, Cavan DA, Everett J. Diabetes—What’s in a name?Diabet Med 1998; 15: 619.
7. Unwin N, Alberti KGMM, Bhopal R, Harland J, WatsonW, White M. Comparison of the current WHO and newADA criteria for the diagnosis of diabetes mellitus in threeethnic groups in the UK. Diabet Med 1998; 15: 554–557.
8. Wiener K, Roberts NB. The relative merits of haemoglobinA1c and fasting plasma glucose as first-line diagnostic testsfor diabetes mellitus in non-pregnant subjects. Diabet Med1998; 15: 558–563.
