38 per cent of adults with type 1 diabetes are misdiagnosed with type 2
Nearly 40 per cent of adults with type 1 diabetes were misdiagnosed and were initially treated for type 2 diabetes, according to new research.
The University of Exeter study found a third of those they analysed were not given insulin, instead they received medication indicated for those with type 2 diabetes.
Further analysis found that half of those misdiagnosed were still being treated as though they have type 2 diabetes 13 years later.
Currently, guidance from the National Institute for Health and Care Excellence (NICE) for the diagnosis of diabetes does not recommend rigorous testing to differentiate between type 1 and type 2 in adults.
Lead researcher Dr Angus Jones, from the University of Exeter Medical School, said: "For people with type 1 diabetes, taking tablets and losing weight are not effective - they need insulin treatment.
"Our research shows that if a person diagnosed as type 2 diabetes needs insulin treatment within three years of diabetes diagnosis, they have a high chance of missed type 1 diabetes. Therefore, they need a blood test to confirm what type of diabetes they have, to ensure they receive the right monitoring, education and treatment."
This study highlights how common misdiagnosing the type of diabetes in adults can be. One high-profile case saw Prime Minister Theresa May, misdiagnosed. She was given type 2 diabetes tablets and lifestyle advice which did not work, and it was only once she was re-tested that doctors discovered she actually had type 1 diabetes.
First study author Dr Nick Thomas, also from the University of Exeter Medical School, said: "While people with type 2 diabetes may eventually need insulin, their treatment and education is very different from type 1.
"If people with type 1 diabetes don't receive insulin they can develop very high blood glucose, and may develop a life threatening condition called ketoacidosis. This means having the right diagnosis is vitally important even if insulin treatment has already been started."
A further problem with long-standing misdiagnosis is that consistently high glucose levels, from not having the right treatment, can greatly increase the risk of developing additional long-term complications such as amputation and heart, eye, kidney and nerve disease. These complications significantly impact upon quality of life as well as presenting significant cost for the NHS.
The research could prompt greater consideration of which type of diabetes is present following a diagnosis of diabetes. The study has been published in the Diabetologia journal.
Type 1 diabetes defined by severe insulin deficiency occurs after 30 years of age and is commonly treated as type 2 diabetes
- Nicholas J. Thomas
- Anita L. Lynam
- Anita V. Hill
- Michael N. Weedon
- Beverley M. Shields
- Richard A. Oram
- Timothy J. McDonald
- Andrew T. Hattersley
- Angus G. Jones
Late-onset type 1 diabetes can be difficult to identify. Measurement of endogenous insulin secretion using C-peptide provides a gold standard classification of diabetes type in longstanding diabetes that closely relates to treatment requirements. We aimed to determine the prevalence and characteristics of type 1 diabetes defined by severe endogenous insulin deficiency after age 30 and assess whether these individuals are identified and managed as having type 1 diabetes in clinical practice.
We assessed the characteristics of type 1 diabetes defined by rapid insulin requirement (within 3 years of diagnosis) and severe endogenous insulin deficiency (non-fasting C-peptide <200 pmol/l) in 583 participants with insulin-treated diabetes, diagnosed after age 30, from the Diabetes Alliance for Research in England (DARE) population cohort. We compared characteristics with participants with retained endogenous insulin secretion (>600 pmol/l) and 220 participants with severe insulin deficiency who were diagnosed under age 30.
Twenty-one per cent of participants with insulin-treated diabetes who were diagnosed after age 30 met the study criteria for type 1 diabetes. Of these participants, 38% did not receive insulin at diagnosis, of whom 47% self-reported type 2 diabetes. Rapid insulin requirement was highly predictive of severe endogenous insulin deficiency: 85% required insulin within 1 year of diagnosis, and 47% of all those initially treated without insulin who progressed to insulin treatment within 3 years of diagnosis had severe endogenous insulin deficiency. Participants with late-onset type 1 diabetes defined by development of severe insulin deficiency had similar clinical characteristics to those with young-onset type 1 diabetes. However, those with later onset type 1 diabetes had a modestly lower type 1 diabetes genetic risk score (0.268 vs 0.279; p < 0.001 [expected type 2 diabetes population median, 0.231]), a higher islet autoantibody prevalence (GAD-, islet antigen 2 [IA2]- or zinc transporter protein 8 [ZnT8]-positive) of 78% at 13 years vs 62% at 26 years of diabetes duration; (p = 0.02), and were less likely to identify as having type 1 diabetes (79% vs 100%; p < 0.001) vs those with young-onset disease.
Type 1 diabetes diagnosed over 30 years of age, defined by severe insulin deficiency, has similar clinical and biological characteristics to that occurring at younger ages, but is frequently not identified. Clinicians should be aware that patients progressing to insulin within 3 years of diagnosis have a high likelihood of type 1 diabetes, regardless of initial diagnosis.
Autoantibodies Classification C-peptide Genetic risk score Type 1 diabetes Type 2 diabetes
DARE Diabetes Alliance for Research in England
T1DGRS Type 1 diabetes genetic risk score
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To our knowledge, this is the first population analysis evaluating the prevalence of type 1 diabetes defined by low endogenous insulin secretion. Our study shows that late-onset type 1 diabetes with severe endogenous insulin deficiency is relatively common (21% of insulin-treated patients) and has very similar characteristics to young-onset type 1 diabetes, but is frequently initially treated as type 2 diabetes. Forty-seven per cent of participants progressing to insulin therapy within 3 years had type 1 diabetes and severe endogenous insulin deficiency, but this was often unrecognised.
Our finding that the clinical features of those with late-onset type 1 diabetes are similar to those with young-onset type 1 diabetes is consistent with recent research using a novel genetic stratification methodology . This showed that 89% of those with genetically defined type 1 diabetes occurring after age 30 required insulin within a year, strikingly similar to the 85% we report using a C-peptide-based definition. This is in contrast to diabetes defined solely by islet autoantibody status, where the phenotype appears intermediate between classical type 1 diabetes and type 2 diabetes in this age group .
A limitation of this study is the cross-sectional design within a relatively homogenous, geographically restricted population. Time to insulin and age of diagnosis were self-reported, and participants were assessed a median 13 years after diagnosis, meaning islet autoantibody positivity will be lower than at diagnosis . Negative autoantibody tests in this context, therefore, do not exclude autoimmune diabetes, and we consider it likely that the aetiology of antibody-negative participants with low C-peptide will be autoimmune, as suggested by the high T1DGRS of these participants (median 0.262, data not shown).
Islet autoantibodies were measured after a longer duration of diabetes in the young-onset cohort compared with those diagnosed later in life, potentially explaining the higher rate of islet autoantibody positivity observed in the late-onset cohort. A further limitation of this study is the lack of availability of a concurrent glucose level when C-peptide was measured; it is recognised that hypoglycaemia can result in a reduced C-peptide result .
These results have clear implications for clinical practice.
They show that type 1 diabetes leading to endogenous insulin deficiency is common in later life but is difficult to identify. Consistent with this, many participants with type 1 diabetes in our cohort were diagnosed and treated as having type 2 diabetes. Without a diagnosis of type 1 diabetes, a patient will not receive appropriate education and will not be eligible for interventions that are often restricted to those with type 1 diabetes, such as carbohydrate counting, continuous glucose monitoring and insulin-pump therapy. They will be at risk of ketoacidosis if insulin is withdrawn.
Our results suggest that if patients are treated as having type 2 diabetes but progress to insulin within 3 years of diagnosis, clinicians should reassess the underlying diagnosis and strongly consider biomarker testing [5, 8, 11].
Type 1 diabetes defined by severe insulin deficiency has similar clinical and biological characteristics to type 1 diabetes occurring at younger ages. However, in later life, patients with type 1 diabetes leading to endogenous insulin deficiency are frequently diagnosed and treated as having type 2 diabetes. Clinicians should be aware that patients progressing to insulin within 3 years of diabetes diagnosis have a high likelihood of having type 1 diabetes, regardless of initial diagnosis.
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