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 about technology that can predict hypoglycemia before it occurs. Which of the following AID features most directly addresses this?
AAutomated meal bolus delivery
BPredictive low glucose suspend
CCarbohydrate-counting algorithm
DProgrammable temporary basal rates
Reveal answer & full explanation
Correct answer: B — Predictive low glucose suspend
AAutomated meal bolus delivery
BPredictive low glucose suspend✓
CCarbohydrate-counting algorithm
DProgrammable temporary basal rates
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
Automated meal bolus delivery — addresses postprandial glucose rather than predicting hypoglycemia; users still bolus manually for meals on current hybrid closed-loop systems (confused-with mealtime dosing)
Carbohydrate-counting algorithm — informs meal dosing, not forward prediction of lows (anchoring on glucose management)
Programmable temporary basal rates — a user-set basal adjustment, not an automated predictive safeguard against hypoglycemia (right-concept-wrong-feature)
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 an automated (hybrid closed-loop) insulin system
BTransition to twice-daily premixed 70/30 insulin therapy
CTransition to a fixed long-acting insulin dose without titration
DTransition to once-weekly subcutaneous semaglutide therapy
Reveal answer & full explanation
Correct answer: A — Transition to an automated (hybrid closed-loop) insulin system
ATransition to an automated (hybrid closed-loop) insulin system✓
BTransition to twice-daily premixed 70/30 insulin therapy
CTransition to a fixed long-acting insulin dose without titration
DTransition to once-weekly subcutaneous semaglutide 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 fixed long-acting insulin dose without titration — removing the ability to titrate would worsen both the elevated HbA1c and the recurrent hypoglycemia; anchoring on "simplify the regimen" ignores her instability.
Transition to once-weekly subcutaneous semaglutide therapy — GLP-1 receptor agonists are not a substitute for insulin in T1DM (absolute insulin deficiency) and do not correct hypoglycemia unawareness; confused-with type 2 diabetes management.
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
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.
References
ADA 2025 — American Diabetes Association Standards of Care in Diabetes—2025 (Diabetes Care 2025; 48 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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