Diagnosing Diabetes. Authors Dr Susan Arnott Lead Clinician, Diabetes MCN Lanarkshire

Transcription

1 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.

2 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: Polydipsia (thirst) polyuria (increased urination) weight loss fatigue recurrent infections loss of consciousness

3 Asymptomatic individuals with 2 or more of the following risk factors for the development of diabetes: 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 for further assistance in therapeutic decision making WHAT TO TEST Random OR fasting plasma glucose HbA1c OGTT (only in certain circumstances) INTERPRETING THE RESULTS Measurement Normal Increased risk of Diabetes Mellitus developing diabetes Random plasma 7.0mmol/l NOT APPLICABLE 11.1mmol/l glucose Fasting plasma 6.0mmol/l mmol/l 7.1mmol/l glucose HbA1c 42mmol/mol 43-47mmol/mol 48mmol/mol 2 hour OGTT plasma glucose 7.7mmol/l mmol/l 11.1mmol/l Consider the following: HbA1c 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.

4 HbA1c 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 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) 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.

5 WHAT TO DO NEXT 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

6 Diagnosing Diabetes A Pragmatic Approach Symptomatic Asymptomatic + 2 or more Risk Factors for Diabetes Fasting or Random Plasma Glucose Fasting Plasma Glucose mmol/l 6.0 mmol/l 7.0 or 11.1 mmol/l HbA1c <42mmol/mol (5.9%) 48mmol/mol (6.5%) 43-47mmol/mol ( %) Diabetes Mellitus Increased Risk of Diabetes Diabetes Services Prevention Strategy Improve wellbeing, screen for, prevent and minimise the impact of micro- and macro-vascular complications Annual HbA1c and risk stratification No intervention required

7 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 Aug 20:137(4): (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: 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 Feb; 21 (1): (abstract) Lawrence JM, Bennet P, Young A, et al; Screening for Diabetes in General Practice: cross sectional population study. BMJ Sept 8; 323 (7312): (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 (7): Petersen JL, McGuire DK; Impaired glucose tolerance and impaired fasting glucose a review of diagnosis, clinical implications and management. Diab Vasc, Dis Res 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): (abstract) Waugh N, Scotland G, McNamee P, et al; Screening for Type 2 Diabetes: Literature Review and Economic Modelling. Health Technology Assess May; 11 (17): iii-iv, ix-xi, (abstract) WHO/International Diabetes Federation; Definition and Diagnosis of Diabetes Mellitus and Intermediate Hyperglycaemia, WHO; Definition, Diagnosis and Classification of Diabetes Mellitus and its Complications, Part 1: Diagnosis and classification of diabetes mellitus,

8 APPENDIX 1 How to perform an Oral Glucose Tolerance Test (OGTT) Advise usual diet and lifestyle for 3 days before the test 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 Exclude the presence of intercurrent infection, other acute illness or trauma and acute psychological stress The test should be carried out in the morning as there is a diurnal variation of glucose tolerance Advise overnight fast for 8-14 hours before the test. Only water may be consumed 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 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) Urine sampling is NOT required Advise the patient to drink 75g anhydrous glucose dissolved in ml 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 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 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 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 The tests are then complete and the patient should be advised to eat and drink normally 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

9 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

10 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