A type 1 diabetes diagnosis isn’t always as straightforward as you might think. That’s because the signs and symptoms of type 1 diabetes can closely resemble those of several other health conditions. Because of this, doctors must carefully rule out other possible diagnoses before confirming type 1 diabetes.

This methodical approach is called making a “differential diagnosis.” If you’re uncertain about the accuracy of your diagnosis, still trying to understand why your blood glucose (blood sugar) is high, or not responding well to prescribed treatments, here’s how a differential diagnosis could help.

Understanding Differential Diagnosis

Health care providers often use a process of elimination to narrow down what’s responsible for certain signs (measurable indicators, like blood glucose levels) and symptoms (what you feel, such as weakness or fatigue). Although these other conditions may not be your final diagnosis, they’re potential causes that need to be considered. This approach of examining various relevant conditions before selecting the appropriate diagnosis is known as making a differential diagnosis.

For example, if you visit the doctor for a cough, the cough is your symptom. To identify the cause, your doctor might consider several possibilities, such as allergies, asthma, or a cold. From there, they will ask questions and run tests to narrow down the list until they determine the most likely diagnosis. Additional testing may then be performed to confirm the diagnosis before recommending treatment options.

Conditions That May Be Mistaken for Type 1 Diabetes

Your doctor may consider certain conditions that mimic the signs and symptoms of type 1 diabetes as part of a differential diagnosis. These include:

• Addison’s disease — Characterized by low levels of cortisol and aldosterone hormones, which are crucial for regulating blood sugar, blood pressure, and electrolyte balance
• Cushing’s syndrome — Results from excessive cortisol production, which can cause high blood sugar levels, weight gain, and high blood pressure
• Graves’ disease (hyperthyroidism) — Involves an overproduction of thyroid hormones, leading to rapid weight loss, increased appetite, and nervousness
• Hashimoto’s thyroiditis (hypothyroidism) — Occurs when the thyroid produces too little hormone, leading to fatigue, weight gain, and muscle weakness
• Cystic fibrosis — A genetic condition that affects the lungs and digestive system and increases the risk of developing diabetes, particularly as one ages
• Monogenic diabetes — A genetic form of diabetes, previously known as “maturity-onset diabetes of youth (MODY)”, that appears in adolescence or early adulthood and may sometimes be mistaken for type 1 diabetes
• Prader-Willi syndrome — A genetic disorder characterized by excessive hunger and obesity, which can also increase the risk of diabetes.
• Type 2 diabetes — Differs from type 1 diabetes in that it’s characterized by insulin resistance and is more common in adults
• Liver, muscle, or fat tissue diseases — Conditions that cause insulin resistance, making it difficult for the body to use insulin effectively and leading to high blood sugar

Sometimes, the side effects of medications like glucocorticoids, thiazide diuretics, and phenytoin can mimic type 1 diabetes. Additionally, symptoms such as peripheral neuropathy (nerve damage that causes numbness, tingling, or pain in the hands and feet) may result from a vitamin B12 deficiency. This can occur after following a restrictive diet or from excessive alcohol consumption.

Sharing your medications, family history, and lifestyle habits is essential to helping your health care provider reach the most accurate conclusion about the root cause of your symptoms. Being open during your medical appointments gives your doctor the most information to work with and helps prevent a misdiagnosis.

Members of myT1Dteam have lived with the consequences of misdiagnosis. “I went 20 years with a type 2 diagnosis,” said one member. “I went into the hospital with diabetic ketoacidosis (DKA). My sodium bicarbonate was less than 2. I had two different doctors tell me today that I should not have made it. It was that trip to the hospital that finally got me the type 1 diagnosis because of the results from antibody testing. My A1c was 11.3. … All that back story to say that three months after DKA and finally getting my diagnosis, I have an A1c of 5.8! Amazing what having the correct meds and a continuous glucose monitor can do.”

Sorting Out the Right Diagnosis of Diabetes

Some cases of type 1 diabetes are particularly tricky to diagnose, especially when it’s not clear whether the person has type 1 diabetes or type 2 diabetes.

Examples of less obvious situations may include:

• A younger person with diabetes who uses insulin but has characteristics associated with type 2 diabetes
• Someone who got diabetes later in life but uses insulin therapy and seems to have type 1 diabetes

Latent autoimmune diabetes of the adult (LADA) blurs the lines between type 1 and type 2 diabetes. While type 1 diabetes usually happens in childhood, LADA occurs later in life, often in older adults. Nonetheless, LADA is similar to type 1 diabetes because it’s an autoimmune disease. If mistakenly diagnosed and treated as type 2 diabetes, LADA can progress more quickly, leading to greater pancreatic beta cell destruction and an increased risk of complications.

Monogenic diabetes may also be mistaken for type 1. This rare syndrome makes up just 5 percent of childhood diabetes cases. Genetic testing can help determine if someone has monogenic diabetes.

Other criteria used to diagnose monogenic diabetes include:

• Diabetes in babies 6 months old or younger
• Family history of diabetes without type 2 risk factors, like obesity
• No islet cell autoantibodies (a sign of type 1 diabetes)
• No obesity or insulin resistance
• High fasting blood sugars in young children or babies

Confirming a Type 1 Diabetes Diagnosis

If your health care provider isn’t quite sure if you have type 1 diabetes, they’ll run multiple tests to confirm the diagnosis. Antibody and genetic tests can be useful in cases when the diagnosis isn’t straightforward. These tests can include:

• Islet autoantibody test — A positive result confirms type 1 diabetes.
• C-peptide test — Levels under 200 picomoles per liter suggest type 1 diabetes.
• Genetic testing for monogenic diabetes — This is used when other results don’t confirm type 1 and type 2 seems unlikely.

Members of myT1Dteam have discussed being diagnosed with type 1 diabetes later in life. “I was recently diagnosed with late-onset type 1 after being admitted to the emergency room for diabetic ketoacidosis,” shared one member. “It’s been a harrowing few weeks since I was discharged from the hospital. I’ve been having to do a lot of research and trial and error on insulin doses, carb intake, exercise, etc. Seeing this community brightened my day!”

Researchers are exploring antibodies beyond islet autoantibodies to aid in diagnosing type 1 diabetes in adults. These include:

• Glutamic acid decarboxylase antibodies (GADA)
• Insulin autoantibodies (IAA)
• Tyrosine phosphatase IA-2 autoantibodies (IA-2A)
• Zinc transporter 8 autoantibodies (ZnT8A)

Seeing a specialist who considers all the details of your situation is crucial for an accurate diagnosis and an effective treatment plan. While doctors strive to provide the best care, it’s important to recognize that medical errors can occur and tests may not always provide definitive results.

If your current diabetes care plan isn’t working as expected, talk to your doctor. They may recommend further evaluation to ensure your diagnosis is correct. You can also seek a second opinion from another provider to explore all possible options.

Talk With Others Who Understand

On myT1Dteam, the social network for people with type 1 diabetes and their loved ones, you can connect with others who understand what you’re going through. Members ask questions, give advice, and share their stories about life with type 1 diabetes mellitus.

When did you first start experiencing blood glucose problems? Did your doctor use a differential diagnosis to figure out what was causing your symptoms? Share your experience below, or start a conversation by posting on your Activities page.