Download Diagnosing Diabetes

Diagnosing Diabetes
Definition of Diabetes Mellitus
The World Health Organisation (WHO) defines diabetes as a metabolic disorder of multiple
aetiology, characterised by chronic hyperglycaemia with disturbances of carbohydrate, fat and
protein metabolism, resulting from defects in insulin secretion, insulin action, or both.
Aims and objectives
The risk of developing diabetes represents a continuum for most people. The diagnosis of diabetes
is traditionally based on the association between the plasma glucose and decompensation to ‘overt’
or symptomatic diabetes. The risk of developing microvascular complications due to chronic
hyperglycaemia, determined by measuring HbA1c can also be used as a hallmark of diabetes as
many people presenting with or without symptoms already have evidence of established
complications that can have a significant impact on their wellbeing.
If a diagnosis of diabetes is made, there must be confidence that the diagnosis is fully established
as the consequences for the individual and the Health Service are considerable and lifelong. This
must be balanced against the minimal clinical consequences of delaying diagnosis in someone at low
risk of developing complications.
This guideline sets out to simplify the process of diagnosing diabetes by incorporating the use of
HbA1c measurement as a diagnostic test, and offer a pragmatic approach to risk classification.
The correlation between HbA1c levels and complications has long been used to establish treatment
goals to prevent the complications of diabetes and maintain or improve well being.
Authors
Dr Susan Arnott – Lead Clinician, Diabetes MCN Lanarkshire
User Group
All those involved with the diagnosis and management of diabetes.
This guideline is not intended to serve as a protocol or standard of care. This is best based on all
clinical data available for an individual case and may be subject to change as scientific knowledge
and technology advances and patterns of care evolve. Adherence to guideline recommendations will
not ensure a successful outcome in every case, nor should it be construed as including all proper
methods of care or excluding other acceptable methods of care aimed at the same result. Ultimately
a judgement must be made by the appropriate healthcare professional(s) responsible for a particular
clinical procedure or treatment plan following discussion with the patient, covering the diagnostic
and treatment options available. It is advised that any significant departure from the guideline
should be documented in the patient’s medical record at the time the decision is taken.
Guideline
BACKGROUND
The requirements for diagnostic confirmation for a person presenting with severe symptoms and
gross hyperglycaemia differ from those for the asymptomatic person with blood glucose values
found to be just above or below the diagnostic cut–off value.
In those with typical symptoms, a random plasma glucose ≥11.1 or a fasting plasma glucose≥7.0 is
sufficient to diagnose diabetes. However, severe hyperglycaemia detected under conditions of acute
infective, traumatic, circulatory or other stress may be transitory and should not in itself be regarded
as diagnostic of diabetes.
The diagnosis of diabetes in an asymptomatic person should never be made on the basis of a single
abnormal blood glucose value. At least one additional abnormal test result with a value in the
diabetes range is essential, either from an HbA1c, fasting blood glucose (for 8-14 hours before the
test), random blood glucose (casual) sample, or from the oral glucose tolerance test (OGTT).
Glycated haemoglobin (HbA1c), reflecting average glycaemia over a period of weeks, is widely
available, standardised and reproducible in Lanarkshire and is therefore suitable to use as a
diagnostic test for diabetes.
If such samples fail to confirm the diagnosis of diabetes mellitus, it is advisable to maintain
surveillance with periodic re–testing until the diagnostic situation becomes clear. In these
circumstances, the clinician should take into consideration any additional risk factors such as:
ethnicity; family history; age; BMI; and concomitant medical history; before deciding on a diagnostic
or therapeutic course of action.
Self monitoring of blood glucose (SMBG), average blood glucose measurement or point of care
HbA1c estimation are not recommended in determining the diagnosis of diabetes.
Note that the accuracy of the HbA1c assay can be affected by conditions where there is an increase
in red cell turnover, haemoglobinopathy and pregnancy. In these circumstances the oral glucose
tolerance test (OGTT) remains the investigation of choice for the diagnosis of diabetes (see
Appendix 1).
As the diagnosis of diabetes can be made using HbA1c the terms Impaired Glucose Tolerance (IGT)
and Impaired Fasting Glycaemia (IFG) become obsolete. They are replaced by a definition of
‘increased risk of developing diabetes.’
WHO TO TEST
Those whose symptoms are suggestive of diabetes at any age:
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Polydipsia (thirst)
polyuria (increased urination)
weight loss
fatigue
recurrent infections
loss of consciousness
Asymptomatic individuals with 2 or more of the following risk factors for the
development of diabetes:
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Age over 40
BMI over 30
Waist circumference over 31.5 inches (80cm) in women, over 37 inches (94cm) in men, over
35 inches (90cm) in South Asian men
Ethnicity (African -Caribbean or Asian origin)
Dyslipidaemia (increase triglycerides, reduced HDL)
Pre-existing cardiovascular disease (including Hypertension, CHD, CVD, PVD)
Past history of Gestational diabetes
Polycystic ovarian syndrome
Family history of Type 2 diabetes in first degree relative
Social deprivation
Consider diabetes risk scoring (QDScore – www.qdscore.org) for further assistance in therapeutic
decision making
WHAT TO TEST
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Random OR fasting plasma glucose
HbA1c
OGTT (only in certain circumstances)
INTERPRETING THE RESULTS
Measurement
Normal
Diabetes Mellitus
≤7.0mmol/l
Increased risk of
developing diabetes
NOT APPLICABLE
Random plasma
glucose
Fasting plasma
glucose
HbA1c
2 hour OGTT
plasma glucose
≤6.0mmol/l
6.1 – 7.0mmol/l
≥7.1mmol/l
42mmol/mol
≤7.7mmol/l
43-47mmol/mol
7.8 – 11.0mmol/l
48mmol/mol
≥11.1mmol/l
≥11.1mmol/l
Consider the following:
HbA1c
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This is the investigation of choice for the diagnosis of diabetes in asymptomatic individuals
Standardised and aligned to the DCCT (Diabetes Control and Complications Trial)/UKPDS (UK
Prospective Diabetes Study) assay
Better index of overall glucose exposure and risk of long-term complications than an isolated
plasma glucose measurement
Substantially less biologic variability than plasma glucose
Substantially less pre-analytic instability than plasma glucose
No need for fasting or timed samples
Relatively unaffected by acute increases in plasma glucose levels
A level 48mmol/mol is significantly sensitive and specific to identify individuals at risk of
developing retinopathy. At levels below this there is no demonstrable increase in this
microvascular complication.
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HbA1c 43-47 mmol/mol = at risk of developing diabetes and although there is no
demonstrable increase in the risk of microvascular complications it does confer an increase in
cardiovascular risk
Currently used to guide management and adjust therapy
Can be misleading where there is abnormal red cell turnover, haemoglobinopathy (HbS, HbC,
HbF, HbE) and pregnancy
In rapidly evolving Type 1 Diabetes when there is an acute elevation of plasma glucose and
typical symptoms an HbA1c may not be diagnostic as not enough time has elapsed for it to
become abnormal
Random or Fasting Plasma Glucose
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A single measurement of fasting plasma glucose will fail to diagnose around 30% of those
with diabetes
If used for diagnosis in asymptomatic individuals pre test fasting advice must be confirmed
and intercurrent acute illness or stress excluded
It is still useful to measure this in those with overt symptoms of diabetes
Oral Glucose Tolerance Test (OGTT) (see Appendices 1, 2, & 3)
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Investigation of choice in pregnancy and conditions of increased red cell turnover
(haemolytic anaemia, major blood loss, blood transfusion) or abnormal haemoglobin
Complex to interpret – if the patient does not comply with the pre-test instructions, fasting
or test conditions or vomits after drinking the glucose load, the results are invalid. If the
wrong bottle is used or is incorrectly labelled, the test is invalid. If there is hypokalaemia at
the time of the test, it is invalid
Time consuming for patients and health care professionals
Lack of suitable environment for waiting for the duration of the test
Costs more than fasting plasma glucose and HbA1c
Less reproducible than fasting plasma glucose and HbA1c
Not useful as an in-patient (recent acute illness, unusual diet, reduced amount of exercise,
increased stress)
If a child requires an OGTT this should be performed in secondary care
In practice any disorder of glucose metabolism necessitates lifestyle intervention and
consideration of cardiovascular risk factors
Special Circumstances - Suspected Gestational Diabetes
The definition and diagnosis of gestational diabetes uses different criteria and investigations should
be directed by a specialist as part of antenatal monitoring.
WHAT TO DO NEXT
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Normal
Consider repeating in 3 years if still considered to have risk factors for the development of
diabetes
Increased risk of developing Diabetes
Recall for repeat HbA1c in 1 year. Patients should be offered advice on lifestyle modification
and minimisation of other risk factors for cardiovascular disease. If the patient is on
treatment for other conditions which can affect glucose metabolism consider substituting for
other agents or reduce the dose of the medication if possible. The risk of progression to
Type 2 Diabetes has been shown to be reduced with lifestyle intervention. Other risk factors
need to be taken into account when estimating each individuals CVD risk. ASSIGN is
recommended for the estimation of CVD risk in Scotland
Type 1 or Type 2 Diabetes Mellitus?
Consider the symptoms, speed of onset, degree of hyperglycaemia, BMI, family history, lipid
profile and co-morbidity. Type 1 diabetes can present beyond the age of 30 years and there
is an increasing prevalence of Type 2 diabetes in the younger population. Offer these
patients support and intervention through the most appropriate Lanarkshire diabetes service
in discussion with the patient. This may be in Primary Care; Community based specialist care
or Acute Care, in isolation or in combination
Diagnosing Diabetes – A Pragmatic Approach
Symptomatic
Asymptomatic + 2 or more
Risk Factors for Diabetes
Fasting or Random
Plasma Glucose
Fasting Plasma Glucose
6.1 – 7.0 mmol/l
≥7.0 or ≥ 11.1 mmol/l
HbA1c
≥ 48mmol/mol (6.5%)
Diabetes Mellitus
Diabetes
Services
Improve wellbeing, screen
for, prevent and minimise
the impact of micro- and
macro-vascular
complications
≤ 6.0 mmol/l
<42mmol/mol (5.9%)
43-47mmol/mol (6.0- 6.4%)
Increased Risk of
Diabetes
Prevention
Strategy
Annual HbA1c and
risk stratification
No
intervention
required
Diabetes MCN endorsement
May 2014
Review Date
May 2017
References
Barr RG, Nathan DM, Meigs JB et al; Tests of glycaemia for the diagnosis of type 2 diabetes mellitus. Ann Intern Med.
2002 Aug 20:137(4):263-72. (abstract)
Davies MJ, Gray IP; Impaired Glucose Tolerance. BMJ 1996 Feb 3; 312 (7026):264-5
Diabetes UK; Position Statement: Early identification of people with Type 2 Diabetes. 2006:
http://www.diabetes.org.uk/Documents/Professionals/Earlyid_TYPE2_PS.doc
Greaves CJ, Stead JW, Hattersley AT, et al; A simple pragmatic system for detecting new cases of type 2 diabetes and
impaired fasting glycaemia in primary care. Fam Pract. 2004 Feb; 21 (1):57-62. (abstract)
Lawrence JM, Bennet P, Young A, et al; Screening for Diabetes in General Practice: cross sectional population study. BMJ.
2001 Sept 8; 323 (7312):548-51 (abstract)
Nathan, D.M. for the International Expert Committee. International Expert Committee report on the role of the A1c assay
in the diagnosis of diabetes. Diabetes Care 2009 32(7):1327-1334. http://care.diabetesjournals.org/content/32/7/1327.full
Petersen JL, McGuire DK; Impaired glucose tolerance and impaired fasting glucose – a review of diagnosis, clinical
implications and management. Diab Vasc, Dis Res. 2005 Feb; 2(1):9-15 (abstract)
Thomas MC, Walker MK, Emberson JR, et al; Prevalence of undiagnosed Type 2 diabetes and impaired fasting glucose in
older British men and women. Diab Med 2005 Jun:22 (6):789-93. (abstract)
Waugh N, Scotland G, McNamee P, et al; Screening for Type 2 Diabetes: Literature Review and Economic Modelling.
Health Technology Assess. 2007 May; 11 (17): iii-iv, ix-xi, 1-125 (abstract)
WHO/International Diabetes Federation; Definition and Diagnosis of Diabetes Mellitus and Intermediate Hyperglycaemia,
2006. http://www.who.int/diabetes/publications/Definition%20and%20diagnosis%20of%20diabetes_new.pdf
WHO; Definition, Diagnosis and Classification of Diabetes Mellitus and its Complications, Part 1: Diagnosis and
classification of diabetes mellitus, 1999. http://whqlibdoc.who.int/hq/1999/who_ncd_ncs_99.2.pdf
APPENDIX 1
How to perform an Oral Glucose Tolerance Test (OGTT)
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Advise usual diet and lifestyle for 3 days before the test
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Withhold or substitute any medication which may affect interpretation of the result
(Appendix 3). If this is not possible it is essential to include this information on the laboratory
request form to assist with interpretation of the result
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Exclude the presence of intercurrent infection, other acute illness or trauma and acute
psychological stress
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The test should be carried out in the morning as there is a diurnal variation of glucose
tolerance
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Advise overnight fast for 8-14 hours before the test. Only water may be consumed
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Take fasting blood sample for plasma glucose estimation – ideally from a warmed vein on
the back of the hand (antecubital fossa samples may be artificially lower). A butterfly
cannula can be used and flushed with saline after taking the fasting sample). A fluorideoxalate tube (grey topped) should be used, filled to the line and gently rotated. The sample
should be labelled with the patient’s identifier and the timing of the test
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At the same time take a blood sample for U&E and creatinine estimation (the test is invalid
if there is hypokalaemia), lipid profile and HbA1c (to aid risk stratification, NOT for diagnostic
purposes)
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Urine sampling is NOT required
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Advise the patient to drink 75g anhydrous glucose dissolved in 250-300ml water over 5
minutes. This is equivalent to 410ml Lucozade (70kcal/100ml formulation). If this is not
possible or the patient vomits the test must be rescheduled
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Advise the patient to remain in a comfortable, stress free environment, limiting physical
activity for 2 hours (i.e. remaining seated as much as possible), within the healthcare
setting. Advise the patient smoking is prohibited during the test
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Take a further blood sample for plasma glucose estimation after the 2 hours. If using a
butterfly cannula draw and discard at least 10mls of blood before sampling for plasma
glucose
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Send both samples to the local laboratory as part of the routine collection clearly indicating
on the request form that it is an OGTT, detailing any drugs which may affect interpretation
of the results. The patient’s CHI number must be included on the request form
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The tests are then complete and the patient should be advised to eat and drink normally
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Rarely reactive hypoglycaemia can occur towards the end of the test period. If there is a
suspicion of this, confirm with a BM test, and counteract with a sugary drink, e.g. more
Lucozade
APPENDIX 2
Oral Glucose Tolerance Test (OGTT)
Patient Information
An Oral Glucose Tolerance Test is one of the tests used to diagnose Diabetes.
Diabetes is a common condition where the amount of glucose (sugar) in the
blood is too high as the body is unable to use it properly.
It is important that you follow these guidelines to ensure that the results are
accurate.
Preparation
• Eat what you would normally eat without any restrictions for at least 3
days prior to the test
• Carry on with your normal activity for at least 3 days before the test
• Do not eat anything for 8- 14 hours before the test, only drink water
during this time
• Smoking is not permitted during the test
• It is important that you are rested during the procedure therefore you
must remain in the Health Centre for the duration of the test. It takes
around 2 hours to complete (you may wish to bring a book or magazine
with you)
The Test
• If you have been asked to bring Lucozade with you it is important that
you bring Lucozade Original and not “sport,” “diet,” “orange” etc,
otherwise the test cannot be carried out. The test requires 410mls of
Lucozade Original therefore you need to make sure you bring the right
size of bottle with you
• At the start of the test you will have a sample of blood taken called your
‘fasting sample’
• You will then be asked to drink a specific amount of Lucozade Original
over a maximum of 5 minutes
• You then need to remain seated in the Health Centre for 2 hours
• A second blood sample will be taken after 2 hours
• The test is now complete
• The blood samples will be sent to the laboratory for analysis
• Your health care professional will advise you when and how to obtain
your results
APPENDIX 3
Drugs affecting the interpretation of an OGTT
The list is extensive. Metformin (used in PCOS) and prednisolone are the key ones. With many of
the others their effect on glucose metabolism may have to be accepted.
Drug Class
Biguanides
Oral glucocorticoids
Thiazide diuretics (alone or as part
of combination preparation)
Loop diuretics
Beta blockers (*less with cardioselective)
Anticonvulsants
Antibiotics
Oestrogens (minimal with HRT)
Anti androgens
Skeletal muscle relaxants
Others
Preparation (for example)
Metformin
Prednisolone, Dexamethasone, Hydrocortisone,
Methylprednisolone
Bendroflumetazide, Hydrochlorthiazde, Indapamide,
Metolazone
Furosemide, Bumetanide
Atenolol, bisoprolol*, carvedilol*, labetalol, metoprolol*,
oxprenolol, propranolol, sotalol
Phenytoin
Nitrofurantoin
Conjugated oestrogens, mestranol, raloxifene, tibolone,
estriol, estradiol, ethinylestridiol, combined oral
contraceptives
Cyproterone acetate
Baclofen
Anabolic steroids, octreotide, danazol