Misdiagnosis of T1D in Adults

Linda Evans was a 40-year-old jogger when she started developing fatigue and increased thirst. After two months, she saw a doctor, who discovered she had elevated blood glucose, diagnosed her with T2D, put her on glipizide and advised a low-calorie diet.

Linda’s fatigue increased so much she could barely work. Her A1C was 8.2 percent. Her doctor stopped the glipizide and started metformin, but she didn’t get better. It took two years with an A1C of more than 8 percent before another doctor tested her for autoantibodies and found she actually had a mild form of T1D, which was later diagnosed as latent autoimmune diabetes of adults (LADA). She was started on a low dose of insulin and improved.

Linda’s experience is commonplace. Someone in their 30s or 40s presents with high blood glucose, and his or her clinician assumes T2D. “It is critical that doctors don’t assume that a hyperglycemic adult has Type 2,” says Dr. Claresa Levetan, an endocrinologist at Chestnut Hill Hospital in Philadelphia. “When an adult comes into my office who doesn’t fit the general profile1 for Type 2 diabetes — that is, he or she has no family history and is not overweight — I immediately order tests to check his or her antibodies.”

We usually think of T1D as a disease of youth, and incidence does peak around puberty. But according to an article in the journal Diabetes, incidence peaks again around age 40.2 An article in the BMJ reported3 that, in the 30–50 age group, T1D accounts for 13 percent of all new cases of diabetes.

According to David Maahs, MD, and associates,4 approximately one fourth of persons with T1D are diagnosed as adults, but diagnosis is often delayed. The result can be delayed treatment or counterproductive treatment. This misdiagnosis can even lead to clinicians’ missing impending ketoacidosis.3

Maybe it’s not T2D

In an article in Diabetes Spectrum, University of Oklahoma Pharmacy professors Katherine S. O’Neal, Jeremy L. Johnson and Rebeka Panak give signs5 that should lead clinicians to consider LADA or T1D in an older person:

• An absence of metabolic syndrome features. People with T2D tend to be heavy and have high blood pressure and bad cholesterol levels. Lacking these symptoms, a hyperglycemic person may well have T1D or LADA.

• Failure of treatment with oral medications.

• Presence of other autoimmune conditions, such as Grave’s disease or rheumatoid arthritis.

• Normal or high levels of physical activity.

• No family history of T2D (although some studies6 have found a family history of T2D in LADA patients).

Testing for LADA or T1D

If any of these clues are present, the patient should be tested for autoantibodies and/or undergo other tests to diagnose impaired insulin production. These tests include:

• Glutamic acid decarboxylase antibodies (GADAs) and islet cell antibodies (ICAs). A person with LADA or T1D will usually test positive for one or both groups7 of antibodies, but several other types may be implicated.

• A C-peptide8 measurement will assess how much insulin-producing capacity a patient has. C-peptide is often undetectable in T1D, high in T2D, and low in LADA.

Simona Cernea, MD, and colleagues wrote in the journal Diabetes Care:

“A well-validated and practical means of quantifying insulin secretion in vivo is measurement of C-peptide levels9 under standardized conditions. An expert panel convened by the American Diabetes Association recommended that C-peptide response (CPR) is the most appropriate measure of function and clinical end point of intervention in human clinical trials.”

• Testing for ketones in blood or urine. Author and Certified Diabetes Educator Gary Scheiner says ketone screening1, helps differentiate between types, because T2D patients “rarely become ketotic.”

Treating adult-onset T1D or LADA

Treatment for autoimmune diabetes in adults should include lifestyle optimization,10 helping people exercise more, eat better and reduce stress.

Metformin, TZDs and other oral antihyperglycemics may help9 if a patient also has insulin resistance. But these drugs have not been well-studied in LADA or T1D.

Low-dose insulin11 should probably be started early, if the patient is willing and able. A study by Kobayashi et al. in Japan found that insulin antibodies were sharply reduced in patients receiving insulin. A study published in the European Journal of Endocrinology found long-term glucose control better in patients who started early insulin.

Sulfonylureas should be avoided because of risk of increasing autoimmunity.12 Sinead Brophy, MD, and associates found that sulfonylureas and insulin together were less effective than insulin alone.

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About our experts: David Spero, BSN, RN, Registered Nurse

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