Autoimmune destruction of pancreatic beta cells leading to absolute insulin deficiency.
Also known as: T1DM, type 1 diabetes, insulin-dependent diabetes, juvenile diabetes, IDDM
Overview
Chronic autoimmune disease characterized by T-cell mediated destruction of pancreatic islet beta cells, resulting in absolute insulin deficiency and lifelong dependence on exogenous insulin to prevent ketoacidosis and death.
Epidemiology
Accounts for ~5-10% of all diabetes. Bimodal peak incidence at age 4-7 and 10-14 years, but can present at any age (including LADA in adults). Higher prevalence in non-Hispanic whites, Scandinavian populations. Strong HLA association (HLA-DR3, HLA-DR4).
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Question 1EndocrineMedium
A 28-year-old female with type 1 diabetes mellitus using a continuous glucose monitor (CGM) and automated insulin delivery (AID) (closed-loop insulin pump) has an HbA1c of 7.2%. She asks whether the pump can use sensor trend data to head off overnight hypoglycemia. Which of the following AID features most directly addresses this?
AProgrammable temporary basal rates
BThreshold-based insulin suspend
CRapid-fall sensor glucose alert
DPredictive low glucose suspend
EExercise mode with a raised target
Reveal answer & full explanation
Correct answer: D — Predictive low glucose suspend
AProgrammable temporary basal rates
BThreshold-based insulin suspend
CRapid-fall sensor glucose alert
DPredictive low glucose suspend✓
EExercise mode with a raised target
Why Predictive low glucose suspend is correct
Predictive low glucose suspend (PLGS) uses continuous glucose monitor (CGM) trend data to forecast hypoglycemia about 30 minutes ahead and automatically suspends basal insulin
This pre-emptive basal suspension reduces nocturnal hypoglycemia by 50-75%
It is the AID feature specifically aimed at predicting and preventing lows before they occur
Why the others are wrong
Exercise mode with a raised target — raises the automated glucose target for planned activity so less insulin is delivered, but it is a user-activated preset tied to exercise rather than a system that reads the sensor trend and suspends insulin ahead of a fall (confused-with activity settings)
Threshold-based insulin suspend — suspends basal insulin only after the sensor glucose has already reached a preset low value, so it reacts to hypoglycemia instead of forecasting it (right-concept-wrong-timing)
Programmable temporary basal rates — a user-set basal adjustment, not an automated predictive safeguard against hypoglycemia (right-concept-wrong-feature)
Rapid-fall sensor glucose alert — it does read the sensor trend, which is what she asked about, but the alert only sounds an alarm when glucose is dropping quickly and does not itself change insulin delivery, so heading off an overnight low depends on her waking and treating rather than on the pump acting automatically (right-data-wrong-action)
Additional high-yield points
Hybrid closed-loop systems (Tandem Control-IQ, Medtronic 780G, Omnipod 5) adjust basal insulin every 5 minutes and may deliver automated correction boluses, but users still bolus manually for meals
Compared with multiple daily injections (MDI), automated insulin delivery (AID) lowers HbA1c by 0.5-1.0%, increases time in range, and reduces hypoglycemia
Question 2EndocrineEasy
A 40-year-old woman with type 1 diabetes managed on multiple daily insulin injections has an HbA1c of 8.9%. Her continuous glucose monitor shows a time-in-range of only 45%, and she reports recurrent nocturnal hypoglycemia and no longer senses the warning symptoms of low glucose. She checks fingersticks regularly and counts carbohydrates accurately. Which of the following is the most appropriate change in her diabetes management?
ATransition to a higher bedtime dose of long-acting insulin glargine
BTransition to an automated (hybrid closed-loop) insulin system
CTransition to an inhaled mealtime insulin regimen
DTransition to adjunctive mealtime pramlintide with her insulin
ETransition to twice-daily premixed 70/30 insulin therapy
Reveal answer & full explanation
Correct answer: B — Transition to an automated (hybrid closed-loop) insulin system
ATransition to a higher bedtime dose of long-acting insulin glargine
BTransition to an automated (hybrid closed-loop) insulin system✓
CTransition to an inhaled mealtime insulin regimen
DTransition to adjunctive mealtime pramlintide with her insulin
ETransition to twice-daily premixed 70/30 insulin therapy
Why Transition to an automated (hybrid closed-loop) insulin system is correct
This patient has type 1 diabetes with poor glycemic control (HbA1c 8.9%, time-in-range 45%) complicated by recurrent nocturnal hypoglycemia and hypoglycemia unawareness, which sharply raises the risk of severe hypoglycemia.
An automated insulin delivery (AID) system couples a continuous glucose monitor, a control algorithm, and an insulin pump; the algorithm reads glucose every few minutes and automatically modulates basal delivery, suspending or reducing insulin when glucose trends downward.
Trials of AID systems (Control-IQ, Omnipod 5, CREATE) demonstrate increased time-in-range above 70% and reduced nocturnal hypoglycemia.
The ADA guideline strongly recommends AID for T1DM, especially with hypoglycemia unawareness, because it helps restore awareness over time.
Why the others are wrong
Transition to twice-daily premixed 70/30 insulin therapy — fixed-ratio premixed insulin lacks the basal-bolus flexibility T1DM requires and increases inter-meal hypoglycemia; right-concept-wrong-setting for type 1 diabetes.
Transition to a higher bedtime dose of long-acting insulin glargine — more bedtime basal chases the elevated HbA1c but deepens the recurrent overnight lows that are driving her hypoglycemia unawareness; anchoring on the A1c ignores what the time-in-range data show.
Transition to an inhaled mealtime insulin regimen — inhaled insulin changes only the prandial component, so it does nothing for basal-driven nocturnal hypoglycemia or for restoring hypoglycemia awareness, and it requires spirometry screening and is contraindicated in chronic lung disease.
Transition to adjunctive mealtime pramlintide with her insulin — pramlintide is an FDA-approved adjunct for type 1 diabetes that modestly lowers HbA1c and postprandial glucose, but it carries a boxed warning for insulin-induced severe hypoglycemia and is contraindicated in hypoglycemia unawareness, so it would compound the very danger driving her management (right-drug-wrong-patient).
Additional high-yield points
Hypoglycemia unawareness results from defective counterregulation after repeated lows; scrupulous avoidance of hypoglycemia for several weeks can restore symptom awareness.
Time-in-range (70–180 mg/dL) targets are generally >70%, with time-below-range (<70 mg/dL) kept under 4% and time <54 mg/dL under 1%.
AID systems still require the patient to bolus for meals ("hybrid" closed-loop), so continued accurate carbohydrate counting remains important.
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Genetic: HLA-DR3/DR4-DQ8 haplotypes (highest risk), family history (5-10% if first-degree relative)
Environmental triggers: enteroviral infection (coxsackie B), early cow's milk exposure, vitamin D deficiency
Other autoimmune disease: Hashimoto thyroiditis, celiac disease, Addison disease, pernicious anemia (polyglandular syndrome type 2)
Pathophysiology
Autoreactive T cells infiltrate pancreatic islets (insulitis) and selectively destroy insulin-producing beta cells. Clinical hyperglycemia emerges when ~80-90% of beta-cell mass is lost. Absolute insulin deficiency leads to unopposed glucagon action, hepatic gluconeogenesis, lipolysis, and ketogenesis. Without insulin, patients cannot suppress ketone production and are at risk for DKA.
Clinical presentation
Symptoms
Classic triad: polyuria, polydipsia, polyphagia
Unintentional weight loss despite normal or increased intake
Fatigue, weakness, blurred vision
May present with DKA as initial manifestation (~30% of pediatric cases): nausea, vomiting, abdominal pain, Kussmaul respirations, altered mental status
Lean young patient with rapid onset of polyuria, polydipsia, weight loss, sometimes presenting in DKA.
Differential diagnosis
Type 2 diabetes mellitus — Older onset, obesity, acanthosis nigricans, family history, gradual onset; insulin resistance with relative deficiency; negative autoantibodies; C-peptide preserved
Latent autoimmune diabetes of adults (LADA) — Adult onset (>30), initial response to oral agents then rapid progression to insulin; positive GAD-65 antibodies; slow autoimmune destruction
MODY (maturity-onset diabetes of the young) — Autosomal dominant family history across 3 generations; onset <25; non-obese; no autoantibodies; preserved C-peptide; HNF1A/glucokinase mutations
Secondary diabetes (pancreatic) — History of chronic pancreatitis, pancreatectomy, hemochromatosis, cystic fibrosis; absent C-peptide; pancreatic exocrine insufficiency
Stress hyperglycemia — Transient elevation during acute illness, sepsis, or trauma in patient without prior diabetes; resolves with recovery
Diagnostic workup
Diagnostic criteria
ADA criteria: A1c ≥6.5%, fasting glucose ≥126 mg/dL, 2-hr OGTT ≥200 mg/dL, or random ≥200 mg/dL with symptoms. T1DM confirmed by positive autoantibodies and/or low C-peptide. With acute symptomatic onset, use plasma glucose rather than A1c, which lags rapidly rising glucose. Staging: stage 1 = ≥2 islet autoantibodies with normal glucose; stage 2 = autoantibodies plus dysglycemia; stage 3 = clinical diabetes. Autoantibody screening is offered to relatives of people with T1DM, and teplizumab can delay stage 3 in selected patients ≥8 years old with stage 2.
Labs
Fasting plasma glucose ≥126 mg/dL on 2 occasions, OR random glucose ≥200 mg/dL with symptoms, OR A1c ≥6.5%, OR 2-hour OGTT ≥200 mg/dL
C-peptide (low or undetectable) — differentiates from T2DM
TSH, TPO antibodies, tissue transglutaminase IgA (screen for associated autoimmune disease)
BMP, urine ketones, blood gas if DKA suspected
Imaging
Not routinely needed for diagnosis
Dilated eye exam 5 years after diagnosis in adults (youth: once diabetes has lasted 3-5 years and age ≥11 or puberty has begun), then every 1-2 years if no retinopathy (contrast T2DM, where the first exam is at diagnosis)
Diagnostic algorithm
Feature
Type 1 DM
Type 2 DM
Age of onset
Usually <30 (any age possible)
Usually >40 (increasing in youth)
Body habitus
Lean or normal weight
Overweight/obese (~80%)
Onset
Acute (weeks); may present with DKA
Insidious (months-years)
Pathophysiology
Autoimmune beta-cell destruction
Insulin resistance + relative deficiency
Autoantibodies
Positive (GAD-65, IA-2, IAA, ZnT8)
Negative
C-peptide
Low or undetectable
Normal or elevated (early)
Ketosis-prone
Yes (absolute insulin deficiency)
Uncommon; can occur with severe stress or infection, SGLT2 inhibitors, or ketosis-prone T2DM (HHS is characteristically non-ketotic)
First-line treatment
Insulin (lifelong)
Lifestyle + metformin
HLA association
HLA-DR3/DR4-DQ8
None
Family history
5-10% in first-degree relatives
Strong (~40% lifetime risk with one affected parent, ~70% if both)
Long-acting basal insulin: glargine (Lantus, Basaglar, Toujeo) or degludec (Tresiba) — once daily; detemir (Levemir) has been removed from the US market
Rapid-acting prandial insulin: lispro (Humalog), aspart (Novolog), glulisine (Apidra) — at meals based on carb counting
Automated insulin delivery (AID, hybrid closed-loop: CGM + pump + algorithm, e.g., Tandem Control-IQ, Medtronic 780G, Omnipod 5) — preferred insulin delivery method in T1DM over MDI, a conventional pump, or a sensor-augmented pump (ADA 2026); the algorithm adjusts basal insulin every few minutes (some systems also give automated correction boluses), but the patient still boluses for meals
Carbohydrate counting and insulin-to-carb ratio education
Second-line / adjunct
Conventional insulin pump (CSII) or sensor-augmented pump — alternatives to MDI when AID is not used; a conventional pump has no dosing algorithm, so a missed meal bolus goes uncorrected
Pramlintide (amylin analog) — adjunct to mealtime insulin in selected patients
Pancreas or islet cell transplant — reserved for refractory hypoglycemia unawareness or end-stage renal disease requiring kidney transplant
Complications
Acute: DKA, hypoglycemia (especially with intensive insulin therapy), hypoglycemia unawareness
Honeymoon phase: transient partial remission after diagnosis with reduced insulin requirements; insulin needs return as residual beta cells fail.
Dawn phenomenon: early morning hyperglycemia from nocturnal growth hormone and cortisol surge; treat by adjusting basal insulin timing.
Somogyi effect: rebound hyperglycemia after nocturnal hypoglycemia (controversial in modern practice with CGM data).
Always check for DKA in any T1DM patient with acute illness, vomiting, or hyperglycemia >250 mg/dL.
Sick-day rules: never stop insulin; check ketones; increase frequency of glucose monitoring; maintain hydration.
Hypoglycemia unawareness: move to AID with CGM alerts and raise glycemic goals to strictly avoid hypoglycemia for several weeks, which can partially restore warning symptoms. Predictive low-glucose suspend stops basal insulin when the CGM forecasts a low about 30 minutes ahead; threshold suspend acts only after glucose has already reached the low limit. CGM targets: time in range (70-180 mg/dL) >70%, time <70 mg/dL <4%, time <54 mg/dL <1%.
References
ADA 2026 — American Diabetes Association Professional Practice Committee. Standards of Care in Diabetes—2026 (Diabetes Care 2026;49 Suppl 1)
DCCT/EDIC — The Effect of Intensive Treatment of Diabetes on the Development and Progression of Long-Term Complications in IDDM (DCCT Research Group, NEJM 1993)
ISPAD 2022 — ISPAD Clinical Practice Consensus Guidelines 2022 — Type 1 Diabetes in Children and Adolescents
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