Why identify people with type 2 diabetes?22
The oral glucose tolerance test 25
Impaired glucose tolerance and impaired fasting glucose 27
Psychological aspects of diagnosis of type 2 diabetes 29
Screening programmes for diabetes 29
The OGTT as a screening test 33
Advice for the person after a screening test 34
Public awareness of diabetes 34
Conclusion 35
References 35
INTRODUCTION
It is known that there is a world epidemic of diabetes and projections have been made that there will be 2.9 million people with diabetes by the year 2010 (Amos et al 1997). As will be clear from Chapter 1, about 80% of these people will have type 2 diabetes, which presents a major challenge to any healthcare system.
Most healthcare professionals would have no difficulties in diagnosing diabetes in a person presenting with the classic symptoms of type 1 diabetes of polyuria, polydipsia, weight loss and tiredness. In such people, the diagnosis is easily confirmed by a clearly elevated blood glucose level confirmed by laboratory testing (Box 2.1) and appropriate treatment commenced. Similarly, it is easy to identify people who clearly do not have diabetes by finding a random plasma glucose below 5.5 mmol/L. Problems most frequently arise when a person is found to have glucose levels between 7.0 mmol/L and 11.1 mmol/L and does not complain of any of the usual signs and symptoms of diabetes.
Box 2.1
Diagnosing diabetes in the person with clinical symptoms
Diagnosing diabetes is clear where there are clinical symptoms and unequivocally elevated blood glucose. Patients with:
▪ symptoms and a random plasma glucose of 11.1 mol/L or above or
▪ a fasting plasma glucose > 7.0 mol/L or above have diabetes as defined by the World Health Organization (WHO 1999).
Diagnosing type 2 diabetes is often more problematic because the onset is very gradual and a person can have diabetes for many years before presenting with complications of the disease (Harris et al 1992, United Kingdom Prospective Study Group (UKPDS) 1998). Hence the challenge to the healthcare team is to identify people with type 2 diabetes before they present with complications of the disease.
WHY IDENTIFY PEOPLE WITH TYPE 2 DIABETES?
Undiagnosed diabetes is not a benign condition. It carries with it costs to the individual – through the onset of complications – and costs to the healthcare system in the treatment of these. Therefore, to diagnose type 2 diabetes prior to complications arising seems a sensible way forward. Coupled with this, the costs of managing people with diabetes globally can be measured in clinical costs, indirect costs and the costs to carers on looking after people with diabetes (WHO 2004). Costs to the UK NHS vary between 8.7% of acute sector costs (Currie et al 1997) to 4.1% for type 2 diabetes alone (Williams et al 2001).
Although the prevalence of type 2 diabetes increases with age, it is now recognised in teenagers (Peters & Davidson 1992, Sinha et al 2002). The UKPDS (1998) found that up to 50% of people presented at diagnosis of diabetes with established complications, particularly retinopathy, indicating that they had diabetes for as long as 12 years. Diabetes remains the leading cause of blindness in working age adults, of end-stage renal disease and of non-traumatic lower extremity amputations; in addition it produces a 2- to 4-fold increase in cardiovascular risk. It is also recognised that mortality rates are higher in the population of people with diabetes whether diagnosed with diabetes or not than in the non-diabetic population (Jarrett & Shipley 1988). Hence the morbidity associated with type 2 diabetes is costly for the individuals concerned.
A random plasma glucose equal to, or exceeding, 11.1 mmol/L is usually indicative of diabetes but a diagnosis should not be made on the basis of only one abnormal finding in the absence of clinical symptoms (WHO 1999). Fiona will be informed that she has diabetes if she has one additional glucose test on another day with a value in the diabetic range (Box 2.2). It is strongly recommended that only plasma venous samples are used to diagnose diabetes (Table 2.1).
Box 2.2
Criteria for diagnosing diabetes in the person without clinical symptoms
A person who is found to have an elevated blood glucose but who does not present with clinical symptoms needs to have two biochemical results on two separate days above the stated range before the diagnosis of diabetes can be made. Results must be one of the following:
▪ A random venous plasma glucose at any time of day regardless of last food intake that is ≥ 11.1 mmol/L
▪ A fasting plasma glucose ≥ 7.0 mmol/L
▪ A 2 hour plasma glucose ≥ 11.1 mmol/L at 2 hours after 75 g glucose in an oral glucose tolerance test
| Patient state | Glucose concentration (mmol/L) | |||
|---|---|---|---|---|
| Whole blood | Plasma | |||
| Venous | Capillary | Venous | Capillary | |
| Fasting | > 6.7 | > 6.7 | > 7.8 | > 7.8 |
| 2 hours after 75 g glucose load | >10.0 | >11.1 | >11.1 | >12.1 |
Fiona’s case study is not uncharacteristic, as people usually present in primary care with other associated medical conditions. The primary healthcare team (PHCT) should be alert to the possibility of undiagnosed diabetes hindering a person’s anticipated recovery, e.g. the slow-to-heal leg ulcer. Likewise, members of the PHCT attending people with a sore toe, vaginal or penile thrush, blurred vision, boils and carbuncles or complaints of weight loss must be proactive in their role to assist in the early detection of diabetes. The PHCT should be aware of the risk factors for developing type 2 diabetes that are frequently associated with undiagnosed diabetes (Box 2.3). These risk factors are only pertinent to the person with type 2 diabetes.
Box 2.3
Risk factors for developing type 2 diabetes
▪ Family history of type 2 diabetes
▪ Obesity, with a body mass index in excess of 25
▪ Increasing age over 40 years
▪ Hypertension or significant hyperlipidaemia
▪ Black and ethnic minorities
▪ Gestational diabetes
▪ Any woman with a history of delivering babies weighing over 4 kg
▪ Women with polycystic ovary syndrome who are obese
▪ People known to have impaired fasting glycaemia
▪ People known to have impaired glucose tolerance
▪ Hypertension or hyperlipidaemia
THE ORAL GLUCOSE TOLERANCE TEST
The oral glucose tolerance test (OGTT) remains the definitive standard for diagnosing diabetes despite the concerns expressed regarding its poor reproducibility and the fact that it is subject to a wide variety of influences (Yudkin et al 1990). The OGTT is still recommended if there is any doubt about the diagnosis (Vaccaro et al 1999, WHO 1999). As a test, however, it is time consuming for the person, can be rather unpleasant and can be quite inconvenient for both people and staff.
It should be remembered that the OGTT is conducted only where there is an equivocal blood glucose result in the absence of any symptoms. It is usually performed within general practice; those hospitals involved in administering the test do so on an outpatient basis. Educating the person before the test is essential as several factors can influence its reproducibility (Box 2.4). This is usually done by nursing staff and can be reinforced by literature. It is important that the person knows who to contact with any queries regarding the test as it can be seen that many factors can influence the result.
Box 2.4
Factors that influence the oral glucose tolerance test
▪ Prolonged bed rest
▪ Restricting diet prior to the test
▪ The length of time in a true fast prior to the test
▪ Any intercurrent illness
▪ Medication that the person may be taking
▪ Smoking prior to or during the test
PROCEDURE
The OGTT should be postponed if the person is unwell or has had a prolonged period of bed rest before the test. The person should take his or her normal diet for 3 days before the test; it is important that diet is not altered prior to the OGTT. The person should fast overnight for 10–16 hours prior to the test, although water may be drunk. The OGTT should be performed in the morning and the person advised not to smoke the night before the OGTT, immediately prior to or during the test. The healthcare professional responsible for the OGTT should record any factor that might influence the interpretation of the results (Box 2.4).
After the test, a return appointment should be made to discuss the results and the person goes home. No particular aftercare is required and the person should be advised to live their life as normal until the return visit.
INTERPRETING THE RESULTS
The WHO criteria for diagnosing diabetes were developed over many years and included research carried out both in the UK and in the USA (WHO 1999). These studies found that people who had a glucose level ≥ 11.1 mmol/L 2 hours after a glucose challenge were at greatest risk of developing microvascular complications of diabetes, primarily retinopathy (Harris 1993), whereas both fasting and postprandial glucose are associated with an increased risk of cardiovascular disease. The criteria used for diagnosing diabetes are outlined in Table 2.1.
Kahlil (in case study 2.2) will not have diabetes if none of his glucose samples exceeds the levels in Table 2.1. He would, however, be advised about his food intake and encouraged to undertake a weight-reduction programme. He would also be advised about taking some exercise to help with his weight management. Due to his family history, his obesity and his ethnic origins, he would be advised to have a screening test for diabetes every 3 years.
Case study 2.2
Kahlil is a 42-year-old business man who has attended his general practitioner for a medical examination for his health insurance. A random blood glucose is 11.5 mmol/L and, as both his parents have type 2 diabetes and the family are of Asian origin, Kahlil is at high risk of developing type 2 diabetes. His body mass index is 27 and he admits that his working day is mainly sedentary; he takes little exercise and frequently has business lunches during the week.
Another scenario is where only one of Kahlil’s results is abnormal. Take, for example, a fasting plasma glucose of 6.0 mmol/L but a 2-hour plasma glucose of 12.1 mmol/L. The second result is clearly within the diabetic range, but Kahlil does not have clinical symptoms of diabetes. In this instance it is recommended that a second result is acquired on another day and both results would be compared. The second result could be obtained from a random sample or repeat OGTT.
Alternatively, Kahlil’s fasting plasma glucose could be normal or elevated but his 2-hour plasma glucose normal. This is not within the diabetic range but is clearly an elevated result. Kahlil would therefore have impaired glucose tolerance that is discussed below.
It is important when interpreting any glucose results that the person reading them knows whether the sample is on whole blood or plasma, venous or capillary, and interprets the results accordingly (Table 2.2). Within the PHCT it is usual for venous plasma samples to be collected.
| Venous plasma glucose | Whole blood glucose |
|---|---|
| 7.0 mmol/n | 6.1 mmol/L |
| 7.8 mmol/n | 6.7 mmol/L |
| 11.1 mmol/n | 10 mmol/L |
In some PHCTs there is a move towards taking a fasting blood glucose instead of undertaking a full OGTT. Although this is not diagnostic, for people who are asymptomatic it can be used as a screening test for diabetes and will be discussed under that heading. The use of fasting glucose levels alone to diagnose diabetes does not appear to identify subjects at increased risk of death due to hyperglycaemia (DECODE Study Group 1999).
DIAGNOSIS AND PREVALENCE
Both these definitions have been clarified under the new classifications system (Box 2.5). The diagnosis of impaired glucose tolerance (IGT) is made only following an OGTT. IGT is typified by hyperglycaemia and insulin resistance.
Box 2.5
Diagnosis of impaired glucose tolerance and impaired fasting glycaemia
The diagnosis of impaired glucose tolerance after an OGTT
People have impaired glucose tolerance (IGT) if their results lie within this range:
▪ Fasting plasma glucose < 7.0 mmol/L and OGTT 2-hour value ≥ 7.8 mmol/L but < 11.1 mmol/L
The diagnosis of impaired fasting glycaemia
People have impaired fasting glycaemia (IFG) if their results lie within this range:
▪ Fasting plasma glucose ≥ 6.1 mmol/L but < 7.0 mmol/L
The prevalence of IGT is between 13% and 40%, depending on studies and population groups (Tringham & Davies 2002). Studies undertaken on multiethnic populations state that between 7% and 72% of the population progress to type 2 diabetes within 5–10 years (Tringham & Davies 2002, Wylie et al 2002), demonstrating that the state of IGT is unstable. The numbers who revert to normal glucose tolerance vary considerably between 28% and 67% (Yudkin et al 1990).
The recognition of IFG identifies people who have a higher-than-normal fasting glucose that is below the diagnostic level for diabetes.
In a study of 167 children and adolescents whose body mass index was above the upper 95% confidence limit for their age, Sinha et al (2002) reported that 25% had IGT and 4% of the adolescents had unsuspected type 2 diabetes. These markedly obese young people were insulin resistant. This study is important in that it documents a strong relationship between childhood obesity and diabetes, with its attendant cardiovascular risks. With the increasing incidence of type 2 diabetes in young people, there is a need for public health efforts to prevent diabetes by encouraging healthier lifestyles in early life.
Gregor has been diagnosed as having IFG. Both IGT and IFT carry important clinical implications. IGT carries an increased risk of macrovascular disease and mortality (DECODE Study Group 1999, Jarrett & Shipley 1988). As with type 2 diabetes, people often present with cardiovascular disease before the diagnosis of IFG is made, as in Gregor’s situation.
A person who is identified as having IGT should be screened for other risk factors, e.g. smoking, obesity, lack of exercise, hypertension and hyperlipidaemia and, thereafter, encouraged to make the necessary lifestyle changes. It is recommended that people with IGT are screened every 3 years for diabetes (Paterson 1993).
There is also evidence that IFG is associated with progression to type 2 diabetes (Vaccaro et al 1999), although evidence in relation to its increased risk of cardiovascular disease is as yet uncertain (Tringham & Davies 2002). Anyone found to have IFG should have an OGTT to exclude the diagnosis of diabetes, hence Gregor’s management would include undertaking an OGTT.
It would appear that there is poor awareness of the clinical significance and management of people with IGT within a primary care setting (Wylie et al 2002). As primary care is the preferred place for screening and diagnosing of diabetes, it is clear that the PHCT need more guidance not only diagnosing these entities but also appreciating the clinical significance of the same and possible prevention strategies.
PREVENTION STUDIES
Several studies have been undertaken on people who have been identified with IGT to determine if there are any interventions that would prevent the progression to type 2 diabetes (Tringham & Davies 2002). Such studies have employed different research methodologies and interventions. Interventions have included lifestyle changes, incorporating exercise regimes, dietary modification and – as a preventive measure – the utilisation of oral medications normally used to treat diabetes. There have been various outcomes to these studies. Some have demonstrated a 58% reduction in progression to diabetes (Pan et al 1997, Tuomilehto et al 2001) with statistical significance for clinical practice demonstrating that progression to diabetes can be delayed by intensive lifestyle changes and by using metformin or acarbose.
People react to the diagnosis of type 2 diabetes in a variety of ways (Lawton et al 2005, Peel et al 2004). There is the perception that type 2 diabetes is not considered serious if the diagnosis is made in primary care without referral to secondary care. People whose diabetes is picked up because of other factors, like Kahlil in case study 2.2, sometimes struggle to conceptualise their illness because they have never felt ill nor experienced any of the side effects of diabetes (Lawton et al 2005). Such individuals do not perceive their lack of adherence to prescribed treatment management as a problem, because they do not actually perceive that they are ill. One study (Lawton et al 2005) demonstrated that people’s perceptions of diabetes were influenced mainly by whether it was their GP or a hospital consultant who informed them of the diagnosis, and whether this took place in primary or secondary care. People can also interpret their lack of referral to secondary care as reflecting the fact that diabetes is not a serious disease and hence, where there is predominantly primary-led care, it is important that individuals are informed about the seriousness of the disease.
Peel et al (2004) found that people arrived at their own diagnosis of diabetes using one of three routes. The first route was where the person suspected that they had diabetes either from prior knowledge from a family member or else through reading about the symptoms on posters, etc. This would be the situation with Kahlil (case study 2.2), both of whose parents had type 2 diabetes and hence, were diabetes to be confirmed, he would almost expect this. The second group identified were those who arrived at their diagnosis through an ‘illness’ route. Fiona, in case study 2.1 epitomises this. People experience some symptoms of hyperglycaemia, have some sort of contact with health professionals and, when a diagnosis is made, there is a feeling of amazement and a sense of relief. The third route was the ‘routine’ route. Here, people were diagnosed with diabetes secondary to other health-related issues like Kahlil (case study 2.2) and Gregor (case study 2.3). These people described a wide range of emotional responses to the diagnosis of diabetes. People diagnosed with type 2 diabetes secondary to other health-related issues pose particular challenges to the healthcare team because they have not actually felt ill and hence might not accept the diagnosis or the proposed treatment. It is therefore essential that it is impressed on such people that diabetes is a serious, life-threatening disease even though their initial management might not appear to reflect this.
Case study 2.1
Fiona is a 55-year-old woman who attends the surgery for a routine hypertension review. Her body mass index is 20 (see Chapter 6) and her blood pressure is 130/80 mmHg; however, a routine urinalysis shows that she has glycosuria. With her consent, a random plasma glucose is taken, which is 13.0 mmol/L. On questioning, she admits to nocturia for a year, which she had attributed to her age and her daily fluid intake. She does not complain of thirst but does enjoy drinking several cups of tea a day. She has had no weight loss within the previous year but admits to feeling tired. Further questioning elicits the fact that she had a ‘touch of sugar’ in her urine during her only pregnancy 30 years previously.
A careful history is taken to ascertain if Fiona is taking any drugs, e.g. corticosteroids or thiazide diuretics, which might reveal an underlying diabetic state. It is also important to enquire about family history, as a positive family history of type 2 diabetes predisposes her towards the same. On questioning, Fiona does not appear to have a family history of diabetes. Her only medication is her hypertensive therapy that she has taken for the preceding 2 years. Her history of gestational diabetes is not surprising as women who have had this are more likely to progress to type 2 diabetes in later life than those without gestational diabetes.
Case study 2.3
Gregor is a 59-year-old man who is admitted to hospital with chest pain. This pain is later confirmed as a reflux oesophagitis. Routine blood tests show that he has a fasting plasma glucose of 6.5 mmol/L. Gregor works as a lorry driver. He is diagnosed with impaired fasting glycaemia.
SCREENING PROGRAMMES FOR DIABETES
How does one detect the large number of people with undiagnosed diabetes? Perhaps the answer is in screening programmes, although there is some debate around these (Engelgau et al 2000, WHO 2003). The concept of screening is not new as there has been a great increase in chronic disease management clinics in primary care over recent years. However, a screening programme can be justified only if it meets certain criteria:
▪ the disease is a significant health problem
▪ sufficient people within the population have the disease
▪ a recognisable asymptomatic stage
▪ clear benefits from early diagnosis
▪ a reliable test to screen for the disease; this should be rapid, simple and safe
▪ obvious benefits from treatment
▪ facilities and costs to meet treatment requirements
▪ screening will be an ongoing process and not a one-off situation.
Type 2 diabetes would appear to be sufficiently prevalent to warrant screening and it meets most of the above criteria (Engelgau et al 2000). There is also some evidence that screening strategies do detect people with previously undiagnosed diabetes (Bandolier 2005). There is increasing evidence that treating diabetes intensively can prevent or delay the development of long-term complications (Diabetes Control and Complications Trial (DCCT) Research Group 1993, UKPDS 1998). It would therefore appear likely that early diagnosis would be beneficial. These benefits are from the perspective of not only the individual con-cerned, but also of the healthcare providers, as the treatment of diabetic complications has a significant impact on health resources. There is, however, little benefit in screening for type 1 diabetes as these people are quickly identified within a matter of days or weeks.
VENUE FOR SCREENING
Health screening can take place in a variety of settings, although predominantly within primary care. Local fairs, mobile health caravans and – more recently – community pharmacies often offer people health checks for blood pressure, weight, diet assessment and could form a basis for screening for diabetes as well. This is known as opportunistic screening. Although screening can occur in any setting, it is important that those doing the screening have adequate knowledge of how to screen for diabetes, the equipment being used, the interpretation of the result and the follow-up advice necessary for those identified as regards requiring further investigation. It is important that professionals involved in any routine screening tests recognise their own limitations within such a setting.
Each PHCT is encouraged to develop its own protocols for screening, although it is acknowledged that there are limited resources to implement a full programme. Population-based screening is expensive and not very sensitive, except in populations in which it is known that there is a high prevalence of diabetes.
Recommendations based on the current consensus of opinion advocate the use of targeted screening for those at high risk of developing diabetes (see Box 2.3; Davies et al 1999, Department of Health (DH) 2001, Engelgau et al 2000). By rationalising screening to target populations, a more cost-effective use of resources is achieved.
It is clear that the responsibility for screening for diabetes is with the PHCTs. By incorporating this into other clinics it need not be an impossible task, an unnecessary burden on staff or a drain on resources. Screening is therefore recommended within the general practice setting (Paterson 1993). PHCTs know the individual patients and their families. They are more able to counsel patients and answer their questions if a screening test is positive. The person being screened should be kept fully informed of the test being used and the result obtained. Each member of the PHCT knows his or her own resources and availability for follow-up. The management of the person starts in general practice and it seems most appropriate that screening for diabetes should be based there too.
The choice of screening test used is decided by the PHCT, which should formulate its own policy regarding this. Identifying a reliable screening test for diabetes is much more difficult.
SCREENING TESTS FOR DIABETES
Any screening programme must use a simple test to discriminate between those who are likely to have the disease and those who are not. For a screening test to be widely acceptable it must be simple, cause little discomfort and be of minimal inconvenience to the person concerned. Any test should be sensitive, specific, reliable and reproducible. That is, a test must have a high probability of being positive when the person actually has the disease (sensitivity) and it must have a high probability of being negative when the person does not have the disease (specificity). The benefits to the person of early diagnosis must be obvious before they consent to screening. One study advocates that, for Caucasians, the OGTT is the choice of method to identify those people at high risk of diabetes (Vaccaro et al 1999).
A variety of screening tests is available and there are advantages and disadvantages with each. Another confounding factor is that there is no differential between cut-off points for screening as opposed to diagnosing diabetes, which can be confusing for practitioners.
Questionnaires have been used as a screening tool but their effectiveness has not been assessed and they are considered to be a poor method (Engelgau et al 2000). Biochemical tests are used for screening, but these are not diagnostic of diabetes but rather indicative that further investigation is required. There are some benefits from using a combination of tests, although this is resource intensive (Engelgau et al 2000, WHO 2003). The most frequently recommended tests for single usage are:
▪ a blood glucose 2 hours after a 75-g glucose load
▪ postprandial glycosuria.
Blood testing
The fasting blood glucose is remarkably constant from day to day in both normal subjects and people with type 2 diabetes. It is a useful test for screening but will inevitably miss those people with mild glucose intolerance whose hyperglycaemia occurs only after a glucose load. A fasting blood glucose test, therefore, has low sensitivity, missing some people who do in fact have diabetes. However, a recent study demonstrated that targeted screening using a questionnaire followed by a fasting plasma glucose was cost effective, sensitive and specific as a screening test to detect asymptomatic type 2 diabetes (Glumer et al 2004).
A fasting blood glucose is fairly easy to acquire. The guidelines for interpreting the results are in Box 2.6. People with an equivocal result should be rescreened in 6–12 months if they have risk factors for diabetes. No further action is required if they have no risk factors.
Box 2.6
Interpreting the result after screening for diabetes using a fasting blood glucose sample (Paterson 1993)
▪ Negative screen: plasma glucose <5.5 mmol/L or whole blood glucose <5.0 mmol/L
▪ Equivocal result: plasma glucose 5.5–6.6 mmol/L or whole blood glucose 5.0–6.0 mmol/L
▪ Positive screen: plasma glucose >6.6 mmol/L or whole blood glucose >6.0 mmol/L
A random blood glucose or postprandial glucose performs better than a fasting glucose as a screening test (Engelgau et al 2000).
Glycated haemoglobin
Although glycated haemoglobin tests are easy to obtain and are not dependent on recent food consumption, they are unsatisfactory as screening tests because of the distribution overlap between diabetic and non-diabetic results. This means that they miss diagnosing people who do have diabetes. One problem is that different laboratories have different techniques for measuring glycated haemoglobin. It is therefore difficult to interpret and compare results between people, the laboratories and the techniques used (WHO 2003). Although each laboratory will have its own range of normal results, there is still an overlap between people who have diabetes and those who do not. All this mitigates against using glycated haemoglobin as a screening test.
Urine testing
A urine test is easy to perform, inexpensive and not too inconvenient for the individual. It might be the screening test of choice for the PHCT, especially when home visiting when other resources might not be so readily available (WHO 2003). Its performance as a screening test is better with random or postprandial testing rather than fasting measures (Engelgau et al 2000).
As stated previously, the renal threshold for glucose rises with age. This means that any glycosuria in an older person is likely to mean that there is a corresponding hyperglycaemia. The presence of glycosuria in the older person will confidently detect diabetes. However, the raised renal threshold also means that some people who have a mildly elevated blood glucose level will go undetected. This is because the mildly elevated blood glucose levels are insufficiently high to produce glycosuria. Hence a negative urine test does not imply the absence of diabetes.
Urine testing when positive (in the absence of pregnancy) will in most cases confidently identify the person with diabetes. However, a positive screening test for glucose means that the person should be referred for further investigations, such as a fasting or postprandial blood glucose. This latter result should be discussed with the person and his or her immediate family or carers, and a management plan implemented with the cooperation of all concerned. However, if the urine test is negative, diabetes cannot be excluded with confidence and the test is, therefore, said to have a low sensitivity. This limits its usefulness as a screening test.
THE OGTT AS A SCREENING TEST
Although WHO has identified the OGTT as the gold standard for the diagnosis of diabetes, it is time consuming and inconvenient for the person and costly to administer on a large scale (WHO 1999). Its use, therefore, as a screening test for diabetes is questionable.
The modified OGTT can be used as a screening test. Here the person being screened consumes a 75-g load of glucose and attends the surgery or screening centre for a blood glucose estimation 2 hours later. A fasting blood glucose is, therefore, not obtained. This unsupervised test clearly depends on cooperation from the individual concerned and understanding of the need to attend exactly 120 minutes after consuming the glucose drink, having consumed no other food in the interim. The guidelines for interpreting the result are detailed in Box 2.7.
Box 2.7
Guidelines for interpreting the result after screening for diabetes using the modified OGTT (Paterson 1993)
▪ Capillary plasma > 8.8 mmol/L or capillary whole blood > 8.0 mmol/L or venous plasma > 8.0 mmol/L is a positive screening test.
This 2-hour postchallenge test is probably the best screening test for diabetes. A negative result correctly identifies most people who do not have diabetes. The test is therefore said to have high specificity. However, it is a more complex test, requires a highly motivated individual, and might be expensive as part of a large screening programme.
It is recommended that those with a positive screening test or equivocal result require a formal diagnosis to be made in line with the WHO criterion detailed above using a full OGTT (Paterson 1993). Individuals should be advised that the test has indicated that there is a possible rise in their blood glucose and that this should be investigated further. They should be instructed to make an appointment to attend their GP’s surgery at their earliest convenience and not to alter their diet in the meantime.
The effects on the person of the possibility of diabetes should not be underestimated. Members of the PHCT must be prepared to counsel such people to help alleviate their anxieties before a definite diagnosis is made. Screening for diabetes might result in people who feel well being told that, in fact, they are ill. This can have implications for their employment prospects, life insurance, driving licence and so on. It is imperative that appropriate advice and counselling is offered to the person being screened at this stressful time. It is further recommended that those with a negative screening test and no risk factors for diabetes should be rescreened every 5 years. Those who have risk factors should be screened every 3 years (Paterson 1993), although it would appear that there is no optimal period for screening (Engelgau et al 2000). However, within the PHCT these recommendations might be considered impossible and hence a decision might be made to develop a team policy to target certain age groups or ethnic minority groups for screening. The frequency of this screening programme will depend on resources within the PHCT.
In Gregor’s situation (case study 2.3), his impaired glucose tolerance was not detected until he presented with another condition. As Gregor does not meet any of the high-risk criteria, he would not be included in any targeted screening programme. Opportunistic screening might detect diabetes; however, increasing public awareness of diabetes could achieve a similar outcome.
PUBLIC AWARENESS OF DIABETES
As diabetes is difficult to diagnose in the absence of clinical symptoms, problematic to screen for, yet has debilitating long-term effects on individuals, perhaps increasing public awareness of the disease could increase the number of people presenting earlier to their GP.
Diabetes UK launched its ‘Missing million’ campaign (Diabetes UK 2000) by suggesting that there might be one million people in the UK with undiagnosed diabetes who require treatment. More recently, some pharmaceutical retailers within the UK have advertised on local television that they will offer a blood glucose test to anyone who requests it.
One study attempted to determine the impact of posters on the knowledge of the public on the symptoms of diabetes (Singh et al 1994). The posters chosen were predominantly in written form and aimed to educate on the symptoms of diabetes; they had a positive tone. It was hoped that this would avoid causing anxiety, which could result in people not seeking help should they have the symptoms. The hypothesis that increasing the general public’s knowledge about the symptoms of diabetes would lead to the early diagnosis of type 2 diabetes was supported (Singh et al 1994). Hence it does compare competitively with other conventional screening methods.
Diabetes has high morbidity and mortality rates. Particular concern is expressed regarding the diagnosing of those people who are as yet unaware that they have the disease. This is because they often present when they already have complications of the disease and early detection of diabetes might assist in the prevention of diabetic complications. The obesity epidemic is further increasing the number of people developing type 2 diabetes at an even earlier age.
Various tests are available to diagnose diabetes, to screen for diabetes and to monitor diabetes (see Chapter 7). It is important that the correct test is used for the correct purpose to facilitate the correct interpretation of the results.
All members of the PHCT have a role to play in the diagnosing of diabetes. Being alert to the possibility of diabetes and adopting the appropriate methods of screening or diagnosing diabetes can identify the newly diagnosed person before the symptoms or complications are evident.
Increasing the knowledge of the general public regarding the symptoms of diabetes through poster campaigns is an effective way to persuade people to self-select for further investigation for diabetes.
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