Type 1 diabetes (T1D) is a chronic condition defined not by lifestyle or diet, but by an autoimmune process where the body’s immune system mistakenly targets and destroys the insulin-producing beta cells within the pancreas. This condition is a progressive disease that unfolds over years, often silently, before any noticeable symptoms appear. Researchers have categorized this progression into three distinct stages, which allows for a more precise understanding of the disease continuum. Identifying these stages before the clinical onset of T1D provides a crucial window for monitoring and potential therapeutic intervention.
Stage 1: Autoimmunity Without Symptoms
Stage 1 is characterized solely by the presence of specific immune markers in the blood. Classification requires testing positive for two or more diabetes-related autoantibodies, which are proteins the immune system produces to attack the body’s own tissues. These autoantibodies often target substances like glutamic acid decarboxylase (GAD), insulinoma-associated protein 2 (IA-2), or insulin itself (IAA). Their presence confirms the autoimmune attack on the beta cells has begun, even though the body is still compensating.
People in Stage 1 remain asymptomatic, meaning they do not experience typical signs of diabetes. This is because the remaining healthy beta cells in the pancreas can still produce enough insulin to maintain normal blood sugar levels, a state known as normoglycemia. The beta cell loss is occurring silently and gradually, which is why this phase can last for months or even many years. For individuals in Stage 1, the lifetime risk of progressing to a clinical diagnosis of T1D approaches 100 percent.
Stage 2: Impaired Glucose Tolerance
The transition from Stage 1 to Stage 2 signifies a measurable decline in the function of the insulin-producing beta cells. While the individual remains asymptomatic, functional beta cell mass has decreased so the pancreas can no longer perfectly manage blood glucose. This inability to keep glucose within the normal range is referred to as dysglycemia, or impaired glucose tolerance.
This stage is confirmed through specific blood tests that reveal abnormal glucose metabolism. For example, an Oral Glucose Tolerance Test (OGTT) may show elevated glucose levels two hours after consuming a sugary drink, or a fasting blood glucose test may be slightly above normal thresholds. An elevated hemoglobin A1c (HbA1c) level, which reflects average blood sugar over the preceding months, may also indicate this subtle impairment.
Stage 3: Clinical Onset and Diagnosis
Stage 3 is marked by the onset of overt symptoms and the need for external insulin therapy. At this point, the destruction of the beta cells is significant, and the remaining cells cannot produce enough insulin to keep blood sugar levels from rising to diagnostic levels. This is the stage where the vast majority of people with T1D are first diagnosed.
The lack of insulin causes glucose to build up in the bloodstream, leading to a cascade of classic acute symptoms. These often include excessive thirst (polydipsia) and frequent urination (polyuria) as the body tries to flush out the excess sugar through the kidneys. Unexplained weight loss and fatigue are also common, as the body cannot use glucose for energy and begins breaking down fat and muscle instead. A serious complication is Diabetic Ketoacidosis (DKA), a life-threatening condition where the body produces high levels of acidic ketones from breaking down fat. For many, DKA is the first event leading to a diagnosis of Type 1 diabetes.
Importance of Screening and Monitoring
Understanding the three stages highlights an opportunity for proactive health management through screening and monitoring. Screening for T1D risk involves a simple blood test to check for the presence of the diabetes-related autoantibodies that define Stage 1. While anyone can be tested, screening is recommended for individuals with a family history of T1D, as they have an increased risk.
Identifying individuals in Stage 1 or Stage 2 allows healthcare providers to establish a structured monitoring plan. This proactive approach significantly reduces the risk of a DKA episode at diagnosis. Knowing a person is in a presymptomatic stage also provides the chance to participate in clinical trials testing new therapies aimed at delaying or preventing the progression to Stage 3. For instance, a person in Stage 2 may be eligible for immunotherapies that have shown success in slowing the beta cell destruction and postponing the need for insulin injections.