Misdiagnosis of Adult-Onset Type 1 Diabetes: Root Cause Analysis

First, a brief summary of the reasons that adults with new-onset Type 1 diabetes are misdiagnosed, followed by a more detailed analysis:

• Persistent myth that Type 1 diabetes is a childhood disease and that adults can’t get it
• Lack of knowledge of the heterogenous phenotype of adult-onset Type 1 diabetes
• Doctors’ lack of time

Why are so many adults with new-onset Type 1 diabetes misdiagnosed? Adult-onset Type 1 diabetes is typically misdiagnosed as Type 2 diabetes, an altogether different disease, based on age not etiology. Misdiagnosis is an epidemic, according to endocrinologist-researcher-professor Dr. Irl B. Hirsch, University of Washington. Interestingly, misdiagnosis is a worldwide problem, occurring in wealthy countries, poorer countries, countries with universal health coverage (Canada, United Kingdom, Australia, etc.), and countries without universal health coverage such as the United States of America. I find it particularly interesting that misdiagnosis is so common in countries with universal health care—logic would say that there would be recognition that appropriate diagnosis and treatment would be about supporting health, well-being, and preventing costly diabetic complications. Even in the USA in a system such as Kaiser Permanente, a fully integrated health system that focuses on keeping its members healthy, misdiagnosis remains a common problem.

There are simple and inexpensive autoantibody tests (GAD, IA-2, IAA, ZnT8, and the older ICA) that can be used to differentiate between Type 1 diabetes (an autoimmune disease) and non-autoimmune diabetes such as Type 2 diabetes. The testing is relatively inexpensive ($55 via JDRF’s T1Detect that was newly launched in December 2020 (https://www.jdrf.org/t1d-resources/t1detect/)), but doctors frequently insist it costs too much in spite of the fact that hospitalization for diabetic ketoacidosis (DKA), which frequently occurs if a person has been misdiagnosed and not treated with insulin, costs an average of $27,000 in the United States. Often the doctor will not perform autoantibody testing because the doctor does not believe it is necessary or appropriate, for the simple reason that they don’t believe that the person has Type 1 diabetes. In the 1970s, the discovery of autoantibodies identified Type 1 diabetes as an autoimmune disease, and in 1977 the first article was published that identified that ~10% of the people diagnosed with Type 2 diabetes were autoantibody positive, had been misdiagnosed, and in fact had Type 1 diabetes. If this knowledge has been available for 44 years, why do we have an epidemic of misdiagnosis?

Medical doctors have been very slow to recognize the prevalence of adult-onset Type 1 diabetes, and the reasons for misdiagnoses I believe are:

• The persistent myth that Type 1 diabetes is a childhood disease, when in fact the majority of new onset Type 1 diabetes is seen in adults [Footnote 1]. Thus, when an adult shows up at a doctor’s office with an elevated blood glucose, the doctor often makes the assumption that the adult has Type 2 diabetes. Since the 1970s and the founding of the Juvenile Diabetes Foundation (now JDRF), the image of sick children has been leveraged to fund research into a disease which is not at all a childhood disease. How do we shift to educating people on the true scope of the problem while not alienating the donors and money that is still needed to research a cure or at least better treatments? Prior to the 1970s, Type 1 diabetes was not viewed as a childhood disease [Footnote 2], and in fact the long-time head of JDRF International, actress Mary Tyler Moore, was diagnosed with Type 1 diabetes at age 33. Other myths are that overweight people, black people, Asian people, and Latino people (BIPOC) don’t get Type 1 diabetes—all of these are false.
• Lack of awareness of the variability in presentation of adult-onset Type 1 diabetes: from Dr. Hirsch’s viewpoint, there is such a heterogeneous phenotype in adult-onset Type 1 diabetes, from a classic phenotype of rapid onset (rapid weight loss, Caucasian, normal BMI, polyuria, polydipsia, polyphagia) to a very slowly progressive Type 1 phenotype (sometimes called LADA (Latent Autoimmune Diabetes in Adults) or SPIIDM (slowly progressive insulin-dependent (Type 1) diabetes mellitus)), that makes it more challenging to correctly diagnose—the presentation of Type 1 diabetes in adults is highly variable. Doctors are not trained or educated on the heterogenous phenotype of adult-onset Type 1 diabetes.
• Doctors’ lack of time (“assembly-line medicine” means that good doctors cannot care for complex patients in 10 or 15 minutes): Both my cousin Diane, a family practice doctor, and Dr. Hirsch say that doctors’ lack of time with patients can lead to misdiagnosis. Dr. Hirsch emphasizes that in the primary care setting, adult-onset Type 1 diabetes is not on the physician’s radar or in their bandwidth. They see so many Type 2s, due to the overwhelming incidence of Type 2 diabetes, and the doctors have so little time. But it is interesting that countries that have universal health coverage still have the epidemic of misdiagnosis—theoretically those doctors should have more time. However, a friend in the UK says that doctors there have even LESS time due to chronic underfunding of medical staff—that lack of time diminishes the quality of care.
• Sound bite nation: we live in a world of instant access to information, non-stop content, and an endless list of things to do. It is no wonder that doctors suffer from the same problem that so many of us struggle with in our everyday lives: not enough time. Just like us, doctors will revert to their “time savers” and “shortcuts” when faced with too many tasks and not enough hours. If a doctor only has 10 minutes with a patient, it is not surprising they once they have “AN” answer, they stop looking and rarely question if they truly found “THE RIGHT” answer. The “art of the interview,” where the doctor asks questions and has the opportunity to listen to the patient is lost due to lack of time—many medical detective doctors will tell you if you can just listen, the patient will provide the answer (disease, diagnosis).
• Many doctors aren’t practicing science they are practicing medicine and doing much by rote. Science requires scientific inquiry, whereas medicine often does not—doctors put a label on a person (adult with elevated blood glucose = Type 2) rather than using scientific methodology to obtain a correct diagnosis. Again, the “lack of time” discussed above can contribute to this. Most doctors will tell you they practice evidence-based medicine—that means someone else designed the study, completed the research, analyzed the findings, and developed the conclusions. The doctor then uses this research to inform their practice, but clearly this is not happening in the case of adult-onset Type 1 diabetes. The best doctors I have had are inquisitive and question everything—they are researchers at heart, medical detectives, and not just medical practitioners.
• Incorrect information is provided by leading health organizations in the United States such as National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), Centers for Disease Control and Prevention (CDC), and the American Academy of Family Physicians (AAFP). The NIDDK website says, “Type 1 diabetes is usually diagnosed in children and young adults,” the CDC website says, “Type 1 diabetes is usually diagnosed in children, teens, and young adults,” and the AAFP website says, “Type 1 diabetes is caused by autoimmune destruction of the islet cells of the pancreas, and onset is typically in childhood,” [Footnote 3] when the majority of new-onset Type 1 diabetes is actually seen in adults. These organizations should be the source of factual and accurate information, not clinging to the myth that Type 1 diabetes is a childhood disease. Organizations such as the CDC should be at the forefront of response to the epidemic of misdiagnosis, not promoting misinformation. Some countries acknowledge that Type 1 diabetes is not a childhood disease; Diabetes Australia, on their website, states that it is a myth that you only get Type 1 diabetes when you are young, and that “new research suggests almost half of all people who develop the condition are diagnosed over the age of 30.” It would be interesting to know if Australia has less misdiagnosis as a result of the greater awareness that people of all ages are diagnosed with Type 1 diabetes.
• Lack of appropriate diagnostic criteria and lack of standard of care: diagnostic criteria for diabetes mellitus is based on fasting plasma glucose or hemoglobin A1c without any differentiation between Type 1 diabetes, Type 2 diabetes, MODY (maturity onset diabetes of the young), and other forms of diabetes. Autoantibody testing is the gold standard for identifying if a person with diabetes has Type 1 autoimmune diabetes, yet this is not part of the diagnostic criteria. In addition, even if a c-peptide test [Footnote 4] is performed, adults with slowly progressive Type 1 diabetes can have a normal range result, and if their doctor believes the myth that “Type 1 means you make no insulin” the person may be diagnosed as having Type 2 diabetes. Additionally, in the United States a medical doctor faces no repercussions if he/she misdiagnoses a person with adult-onset Type 1 diabetes and provides inappropriate or substandard treatment. The American Association of Clinical Endocrinologists (AACE) now suggests that autoantibody testing be performed to differentiate between Type 1 diabetes and non-autoimmune diabetes (Type 2, MODY, etc.), but it is not a requirement. Thus, there is no obligation to diagnose, classify, and appropriately treat the different diseases that fall under the term “diabetes.” If there were a standard or guideline, doctors would be held accountable to the minimum standard of care: anything less would be malpractice.

I welcome your thoughts on the root causes of misdiagnosis—did I miss one? My next blog will be on possible solutions.

Footnote 1: Miriam E Tucker, “Half of All Type 1 Diabetes Develops after 30 Years of Age.” Medscape, September 20, 2016. [Note that this study found that 50% of people diagnosed with Type 1 diabetes were diagnosed older than 30 years (and the study subjects only went up to 60 years, so greater than 50% are diagnosed over the age of 30)]. The Medscape article is based on data presented September 16, 2016, at the European Association for the Study of Diabetes (EASD) 2016 Annual Meeting by Dr Nicholas JM Thomas, of the Institute of Biomedical and Clinical Science, University of Exeter Medical School, United Kingdom (later published as Frequency and phenotype of type 1 diabetes in the first six decades of life: a cross-sectional, genetically stratified survival analysis from UK Biobank. Lancet Diabetes Endocrinol. 2018 February; 6(2): 122-129). See also "Most New Onset Type 1 Diabetes Occurs in Adulthood: It is Time to Dispel the Myth that Type 1 Diabetes is a Childhood Disease" link here

Footnote 2: See my blog "Historical References to Adult-Onset Type 1 diabetes: How Did Type 1 Diabetes Ever Become Defined as a Childhood Disease?" link here

Footnote 3: All websites viewed on December 30, 2020.

Footnote 4: The beta cells in the pancreas produce insulin and C-peptide, and testing for c-peptide measures how much endogenous insulin a person is making. Typically, people with rapid onset Type 1 diabetes will have low levels of c-peptide, indicating insufficient insulin production, but often people with slowly progressive Type 1 diabetes have normal to slightly low c-peptide levels. People with true Type 2 diabetes tend to have high c-peptide levels. 

CREDIT AND THANKS: to Brea Di Dato, Chris Petersen, Brande Gentry, and Jenny Coe, who reviewed this blog and made excellent suggestions