# Type 1 Diabetes

Type 1 diabetes requires lifelong physiologic insulin replacement, early continuous glucose monitoring, and structured prevention of hypoglycemia and ketoacidosis. Accurate classification—including adult-onset autoimmune disease—guides urgent insulin initiation, technology selection, sick-day planning, and referral for disease-modifying or beta-cell replacement options.

**Clinical question:** How should physicians diagnose, treat, monitor, and prevent acute complications in type 1 diabetes?

Updated: 2026-08-21T00:06:25.768346Z

## What matters in practice
- Treat type 1 diabetes with basal plus prandial insulin by multiple daily injections or continuous subcutaneous infusion; insulin analogs are preferred when feasible to reduce hypoglycemia. [17]
- Offer continuous glucose monitoring early and automated insulin delivery to adults who can use the technology safely; both improve glycemic outcomes and reduce hypoglycemia. [17]
- For many nonpregnant adults, reasonable goals are A1C below 7%, CGM time in range 70-180 mg/dL above 70%, time below 70 mg/dL below 4%, and time below 54 mg/dL below 1%. [21]
- Any level 2 or 3 hypoglycemia should trigger reassessment of insulin dosing, technology, education, and individualized glycemic targets; prescribe ready-to-use glucagon for insulin-treated patients. [21]
- Do not use SGLT2 inhibitors for type 1 diabetes in the United States; they increase diabetic ketoacidosis risk, which may be euglycemic. [17]

## Confirm autoimmune insulin deficiency and avoid adult misclassification

Classification determines urgency of insulin replacement and informs prognostic counseling.

Type 1 diabetes results from autoimmune beta-cell destruction and near-absolute insulin deficiency; insulinopenia predisposes to catabolism, hypertriglyceridemia, and diabetic ketoacidosis (DKA). [17] In adults, autoimmune diabetes is commonly misclassified as type 2 diabetes, delaying insulin and increasing DKA risk. Islet autoantibodies, particularly GAD antibodies with other islet autoantibodies, and C-peptide interpreted with concurrent glucose help resolve diagnostic uncertainty. [12]

At presentation with symptomatic hyperglycemia, weight loss, ketosis, or suspected insulin deficiency, assess plasma glucose, electrolytes, bicarbonate, pH, and beta-hydroxybutyrate promptly. DKA requires diabetes or glucose at least 200 mg/dL, beta-hydroxybutyrate at least 3.0 mmol/L or urine ketones at least 2+, and pH below 7.3 and/or bicarbonate below 18 mmol/L. [21] A prior diabetes history can satisfy the diabetes criterion in euglycemic DKA. [21]
- Order islet autoantibodies and C-peptide with glucose when phenotype or clinical course is discordant with presumed type 2 diabetes, particularly in adults with early insulin need, ketosis, or unexplained treatment failure. [12]
- Treat suspected insulin deficiency immediately; diagnostic testing should not delay insulin when ketosis or catabolic illness is present. [17][21]

*Acute hyperglycemic crisis criteria relevant to suspected type 1 diabetes. [21]*

| Condition | Required criteria | Immediate implication |
| --- | --- | --- |
| DKA | Glucose at least 200 mg/dL or known diabetes; beta-hydroxybutyrate at least 3.0 mmol/L or urine ketones at least 2+; pH below 7.3 and/or bicarbonate below 18 mmol/L. [21] | Urgent treatment and evaluation for precipitating illness, missed insulin, or pump interruption. [21] |
| HHS | Glucose at least 600 mg/dL; effective osmolality above 300 mOsm/kg or total osmolality above 320 mOsm/kg; beta-hydroxybutyrate below 3.0 mmol/L or urine ketones below 2+; pH at least 7.3 and bicarbonate at least 15 mmol/L. [21] | Immediate inpatient evaluation and treatment; mixed DKA-HHS presentations occur. [21] |

## Use physiologic insulin replacement, not basal insulin alone

Every patient requires continuous basal insulin plus nutritional and correction insulin.

ADA guidance recommends either continuous subcutaneous insulin infusion or multiple daily injections of basal plus prandial insulin for most adults with type 1 diabetes. [17] Insulin analogs or inhaled prandial insulin are preferred over injectable human insulin when feasible because they reduce hypoglycemia risk. [17] A basal-bolus regimen includes basal insulin for fasting and between-meal control plus rapid- or ultra-rapid-acting prandial insulin for meals and correction. [17]

For metabolically stable adults, total daily insulin is often initiated around 0.5 units/kg/day, with approximately 30%-50% as basal insulin and the remainder as prandial insulin; requirements vary with residual endogenous insulin, age, puberty, illness, menses, pregnancy, diet, and activity. [17] The source supports this as a typical starting framework, not a fixed dose algorithm. Reassess insulin-taking behavior, access, technique, and regimen every 3-6 months. [17]

Teach carbohydrate-based meal dosing, correction dosing based on current glucose and trends, adjustment for anticipated activity, and sick-day management. [17] Fat and protein can affect postprandial glycemia and may require individualized adjustment, especially with pump therapy. [17] Inspect injection and infusion sites routinely; lipohypertrophy causes erratic absorption, glycemic variability, and unexplained hypoglycemia. [17]
- Pump users need explicit backup long-acting insulin and ketone-action plans: interruption of rapid-acting pump delivery can lead quickly to ketosis or DKA. [17]
- Consider inhaled insulin only after considering pulmonary constraints; it is contraindicated in chronic lung disease such as asthma or COPD, not recommended for current or recent smokers, and requires spirometry before and after initiation. [17]
- Pramlintide is FDA-approved adjunctive therapy for adults with type 1 diabetes, but expected benefits are modest: A1C reduction of 0.3%-0.4% and approximately 1 kg weight loss in trials. [17]

### Adjunctive therapies

Metformin has produced small reductions in weight, insulin dose, and lipids in adults with type 1 diabetes without durable A1C improvement. GLP-1 receptor agonists, including liraglutide, have shown modest A1C lowering and weight loss in trials but are not approved for type 1 diabetes; semaglutide and tirzepatide evidence is currently limited to retrospective case series in people with obesity. [17]
- SGLT2 inhibitors are not FDA-approved for type 1 diabetes. Their use is associated with increased DKA, including episodes with glucose below 200-250 mg/dL; avoid in patients with prior DKA. [17]

*Insulin delivery choices for adults with type 1 diabetes. [17]*

| Approach | Best use and advantages | Key hazards or limitations |
| --- | --- | --- |
| Multiple daily injections | Basal long-acting analog plus meal and correction rapid-acting or ultra-rapid insulin; flexible meal timing and content. [17] | At least four injections daily; requires meal dosing skills; long-acting analog may not address marked dawn phenomenon as effectively as pump therapy. [17] |
| Pump or automated insulin delivery | Programmable basal delivery and meal/correction boluses; hybrid closed-loop systems provide the highest time in range and lowest time below range among pump approaches described. [17] | Cost, device burden, technical complexity, skin reactions, infusion-site infection, and rapid ketosis/DKA if delivery is interrupted. [17] |
| Human insulin regimens | May be necessary when affordability limits analog use. [17] | NPH and regular insulin require more consistent meals and timing and carry greater nocturnal or delayed postprandial hypoglycemia risk. [17] |

## Use CGM metrics to guide insulin changes and hypoglycemia prevention

A1C alone misses glycemic variability and hypoglycemia.

Assess glycemia with A1C and/or CGM metrics. [21] For people using CGM, review at least 14 days with active data at least 70% of the time for pattern management. [21] In most nonpregnant adults, target time in range of 70-180 mg/dL above 70%, time above 180 mg/dL below 25%, time above 250 mg/dL below 5%, time below 70 mg/dL below 4%, and time below 54 mg/dL below 1%. [21]

For many nonpregnant adults, an A1C goal below 7% is appropriate, with preprandial glucose 80-130 mg/dL and peak postprandial glucose below 180 mg/dL measured 1-2 hours after beginning a meal. [21] Goals must be relaxed when treatment burden or hypoglycemia risk exceeds expected benefit. [21] A1C is unreliable with altered erythrocyte turnover, including anemia, recent transfusion, erythropoiesis-stimulating therapy, end-stage kidney disease, and pregnancy; use CGM, blood glucose, fructosamine, or glycated albumin as appropriate. [21]

Early CGM improves glycemic outcomes and quality of life and reduces hypoglycemia in adults with type 1 diabetes. [17] ADA recommends offering automated insulin delivery to all adults with type 1 diabetes; selection should account for ability to use the system safely, caregiver support, preferences, cost, and access. [17]
- Measure A1C or other glycemic metrics at least twice yearly when stable and at goal; assess about every 3 months after treatment changes, when goals are unmet, or after frequent/severe hypo- or hyperglycemia. [21]
- For older adults using CGM, less stringent goals include time in range above 50% and combined time below 70 mg/dL below 1%. [21]

*CGM targets for nonpregnant adults with type 1 or type 2 diabetes. [21]*

| Metric | Most adults | Older adults |
| --- | --- | --- |
| Time in range, 70-180 mg/dL | >70%. [21] | >50%. [21] |
| Time below range, 54-69 mg/dL | <4%, including time below 54 mg/dL under 1%. [21] | <1%, including time below 54 mg/dL under 1%. [21] |
| Time above range, 181-250 mg/dL | <25%; time above 250 mg/dL <5%. [21] | <50%; time above 250 mg/dL <10%. [21] |
| Glucose coefficient of variation | ≤36%. [21] | ≤36%. [21] |

## Prevent hypoglycemia and DKA at every encounter

Both complications require structured education, equipment access, and regimen revision.

Review hypoglycemia at every visit in all patients at risk and screen at least annually for impaired awareness. [21] Level 1 hypoglycemia is glucose below 70 mg/dL and at least 54 mg/dL; level 2 is below 54 mg/dL; level 3 is altered mental or physical status requiring assistance, regardless of measured glucose. [21] Level 2 or 3 events require prompt treatment-plan reassessment, including insulin deintensification or modification when appropriate. [21]

Prescribe glucagon for all people taking insulin or at high risk for hypoglycemia, and train family, caregivers, school staff, or others likely to assist. Ready-to-use formulations are preferred over products requiring reconstitution. [21] For a conscious patient with glucose below 70 mg/dL, administer fast-acting glucose-containing carbohydrate, recheck after 15 minutes, and repeat treatment if hypoglycemia persists. [21]

DKA prevention requires explicit sick-day rules. Patients on intensive insulin therapy should not stop basal insulin when not eating. [21] In those at risk, advise blood or urine ketone testing during illness, missed insulin, symptoms of DKA, or glucose above 200 mg/dL. [21] Patients who cannot tolerate oral hydration, do not improve with insulin, have altered mental status, or have worsening illness require immediate medical evaluation. [21]
- Major hypoglycemia risk factors include recent level 2 or 3 hypoglycemia, impaired awareness, intensive insulin therapy, end-stage kidney disease, cognitive impairment, food insecurity, housing insecurity, and underinsurance. [21]
- Ask patients with recurrent lows whether they always feel hypoglycemia; a negative response warrants further assessment for impaired awareness. [21]
- Review access to insulin, monitoring supplies, ketone testing, glucagon, and backup injection supplies after any DKA or severe hypoglycemia event. [21]

*High-yield self-management actions for acute glucose risk. [21]*

| Clinical situation | Patient action | Escalation threshold |
| --- | --- | --- |
| Conscious hypoglycemia below 70 mg/dL | Use glucose-containing fast carbohydrate; recheck at 15 minutes and repeat if persistent. [21] | Use glucagon when oral carbohydrate cannot be taken; reassess regimen after level 2 or 3 events. [21] |
| Illness, missed insulin, or glucose above 200 mg/dL in a ketosis-prone patient | Increase glucose monitoring and check urine or blood ketones; continue basal insulin. [21] | Seek urgent care for inability to hydrate orally, nonresponse to insulin, altered mental status, or worsening illness. [21] |
| Pump delivery interruption | Treat as potential insulin deficiency; use backup insulin plan and check ketones when hyperglycemic or symptomatic. [17][21] | Urgent evaluation for ketonemia, acidosis symptoms, or persistent hyperglycemia. [21] |

## Refer selected patients for disease modification or beta-cell replacement

These options are reserved for defined clinical scenarios and specialized centers.

Stage 2 type 1 diabetes is presymptomatic autoimmune diabetes with dysglycemia. Teplizumab is the only FDA-approved disease-modifying therapy to delay progression from stage 2 to clinical stage 3 disease; FDA approval now includes children aged 1 year and older. [4] Identification of at-risk individuals through screening enables specialist assessment and discussion of treatment burden, adverse effects, and expected delay in clinical disease. [4]

Pancreas or islet transplantation can normalize glucose and mitigate microvascular complications but requires lifelong immunosuppression. [17] Pancreas transplantation should generally be reserved for people undergoing kidney transplantation, after kidney transplant, or with recurrent DKA or severe hypoglycemia despite optimized management. [17]

Donislecel-jujn (Lantidra) is the FDA-approved allogeneic deceased-donor islet cell therapy for adults with type 1 diabetes who cannot approach target A1C because of repeated severe hypoglycemia despite intensive diabetes management and education. [1] It is infused into the hepatic portal vein; additional infusion may be considered based on response. [1] In two nonrandomized single-arm studies of 30 participants, 21 achieved insulin independence for at least 1 year, including 10 for more than 5 years; five achieved no insulin-independent days. [1] Procedure and immunosuppression-related serious adverse reactions were common and can lead to loss of graft function if immunosuppression must be discontinued. [1]
- Refer recurrent severe hypoglycemia or hypoglycemia unawareness despite optimized CGM, automated insulin delivery, education, and psychosocial intervention to an experienced diabetes/transplant center for advanced-therapy assessment. [1][17][21]

*Advanced interventions in type 1 diabetes. [1][4][17]*

| Intervention | Candidate | Major trade-off |
| --- | --- | --- |
| Teplizumab | Stage 2 type 1 diabetes; FDA indication includes patients aged 1 year and older. [4] | Delays stage 3 onset but requires specialist assessment and treatment-burden discussion. [4] |
| Pancreas transplantation | Usually simultaneous with, or after, kidney transplantation; may be considered for recurrent DKA or severe hypoglycemia despite optimized care. [17] | Surgical risk and lifelong immunosuppression. [17] |
| Donislecel-jujn | Adults with repeated severe hypoglycemia who cannot approach A1C targets despite intensive management and education. [1] | Portal-vein infusion and lifelong immunosuppression; serious procedure- and immunosuppression-related adverse events. [1] |

## Common questions

### When should adults thought to have type 2 diabetes be evaluated for type 1 diabetes?

Evaluate autoimmune diabetes when adult presentation includes ketosis, catabolic weight loss, early insulin requirement, unexpected treatment failure, or phenotype-course discordance. Use islet autoantibodies and C-peptide interpreted with concurrent glucose; do not delay insulin in suspected insulin deficiency. [12][17]

### What should trigger insulin regimen reassessment in type 1 diabetes?

Reassess promptly after level 2 or 3 hypoglycemia, recurrent level 1 events, significant glycemic variability, DKA, pump interruption, treatment-access barriers, or failure to meet individualized A1C or CGM targets. [17][21]

### Are GLP-1 receptor agonists or SGLT2 inhibitors appropriate in type 1 diabetes?

Pramlintide is approved as adjunctive treatment in adults. GLP-1 receptor agonists and metformin have limited adjunctive evidence but are not approved for type 1 diabetes. SGLT2 inhibitors are not FDA-approved and increase DKA risk, including euglycemic DKA. [17]

## References
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## Editorial note

Prepared from cited clinical literature using Astra's research workflow. Verify recommendations against current guidance and patient-specific factors.