Type 1 Diabetes Mellitus (T1DM)
NICE guideline [NG17] Type 1 diabetes in adults: diagnosis and management. Last updated: Aug 2022.
NICE CKS Diabetes – type 1. Last revised: Dec 2024.
Background Information
Definition
T1DM is defined as:
- Chronic condition resulting from autoimmune destruction of pancreatic β-cells,
- Leading to an absolute deficiency of insulin and consequent hyperglycemia
Pathophysiology
Autoimmune response → progressive destruction of pancreatic β cells in the islets of Langerhans → absolute insulin deficiency → hyperglycaemia (due to reduced glucose uptake in peripheral tissue)
Risk Factors
The primary risk factor is genetic predisposition: [Ref1][Ref2]
- HLA-DR3-DQ2
- HLA-DR4-DQ8
Environmental risk factors may trigger or accelerate autoimmune response: [Ref1][Ref2]
- Enteroviruses
- Respiratory tract infections
- Alterations in the gut microbiome
- Early life factors (e.g. rapid weight gain, childhood obesity)
T1DM is also associated with other autoimmune conditions (“autoimmune march”):
- Addison’s disease
- Autoimmune thyroid disease (Hashimoto’s thyroiditis, Graves’ disease)
- Coeliac disease
- Autoimmune gastritis (including prenicious anaemia)
- Vitiligo
- Less commonly – autoimmune hepatitis, rheumatoid joint disease, psoriasis, uveitis
Clinical Features
Up to 1/3 of children and adolescents with T1DM present with DKA [Ref]
Classic symptoms (NOT specific to T1DM): [Ref]
- “3 Ps” – classic symptoms of hyperglycaemia
- Polyuria
- Polydipsia
- Polyphagia
- Unexplained weight loss
- Fatigue
- Blurred vision
- Recurrent infections / poor wound healing
Be aware that the classic symptoms stated above are NOT specific to any type of diabetes. They are simply consequences of hyperglycaemia affecting various body systems.
Features / factors that suggest T1DM over other types of diabetes:
- Ketosis
- Rapid weight loss
- Onset <50 y/o
- BMI <25 kg/m2
- Personal and/or family history of autoimmune disease
Complications
Acute Complications
Important acute complications: [Ref]
- DKA – see this article for more details
- New-onset T1DM (1/3 of children and adolescents present initially as DKA)
- DKA can otherwise occur due to absolute or severe insulin deficiency (e.g. omission or interruption of insulin therapy, infection, illness, stress, alcohol use)
- Severe hypoglycaemia (often due to insulin therapy)
Chronic Complications
Microvascular complications: [Ref]
- Diabetic retinopathy
- Diabetic nephropathy
- Diabetic neuropathy +/- charcot arthropathy
- Diabetic autonomic neuropathy
- Gastroparesis
- Sexual dysfunction
- Orthostatic hypotension
- Abnormal sweating
Macrovascular disease (from atherosclerosis): [Ref]
- Coronary artery disease
- Cerebral vascular disease
- Peripheral arterial disease
Diabetic foot problems – arise from a combination of peripheral arterial disease and diabetic neuropathy
- See this article for more details
Diagnosis
Step 1 – Diagnose Diabetes
Diabetes mellitus diagnostic rules:
- Typical symptoms + 1 abnormal test, or
- Asymptomatic + 2 abnormal tests (same test on different day or 2 different tests on the same day)
The biochemical cut-offs for diagnosing diabetes mellitus are the same regardless of type:
| Test | Diabetes Cut-off | Pre-Diabetes |
|---|---|---|
| Fasting plasma glucose | ≥7.0 mmol/L | 6.1-6.9 mmol/L (impaired fasting glucose) |
| Random plasma glucose | ≥11.1 mmol/L | n/a |
| 2-hour post-oral glucose tolerance test | 7.8-11.0 mmol/L (impaired glucose tolerance) |
A ‘finger prick’ capillary blood glucose level CANNOT be used to diagnose diabetes mellitus.
HbA1c has a limited role in diagnosing T1DM. This is because HbA1c measures the average blood glucose over the past 2-3 months. Given the rapid onset and progression of hyperglycaemia in T1DM, it is less sensitive.
HbA1c is generally NOT recommended to diagnose diabetes in the following scenarios: [Ref]
- All children and young people.
- Pregnancy – current or recent (< 2 months).
- Suspected type 1 diabetes, regardless of age
- Short duration of diabetes symptoms (< 2 months)
- Patients at high risk of diabetes who are acutely ill
- Patients recently taking (for < 2 months) medication that may cause rapid glucose rise (e.g., corticosteroids, antipsychotic drugs)
- Acute pancreatic damage or pancreatic surgery
- Renal failure
- Human immunodeficiency virus (HIV) infection
Step 2 – Confirm T1DM
Once diabetes is confirmed based on the above-stated hyperglycaemia cut-offs. The next thing is to decide whether this is T1DM or other types of diabetes:
NICE states that T1DM patients typically have at least 1 of the following features (but not always):
- Ketosis
- Rapid weight loss
- Onset <50 y/o
- BMI <25 kg/m2
- Personal and/or family history of autoimmune disease
Tests
- 1st line: diabetes-specific autoantibodies
- GAD autoantibodies
- IA-2 autoantibodies
- ZnTa autoantibodies
- Insulin autoantibodies
- 2nd line: serum C-peptide (non-fasting)
- Only measure C-peptide if there are -ve autoantibodies and the type of diabetes remains uncertain
- ↓ / undetectable levels strongly suggest insulin deficiency (typical of T1DM)
Management
General / Conservative Management
Offer all patients a structured education programme (e.g. DAFNE)
Offer dietary advice:
- Carbohydrate counting training
- Healthy eating and a balanced diet
Optimise blood pressure control, the target is guided by urine ACR
- <70 mg/mmol → normal target
- ≥70 mg/mmol → reduced target (<130/80 mmHg)
- NB for adults >80 y/o, the BP target is <150/90 mmHg irrespective of urine ACR
IMPORTANT, advice on sick-day rules to avoid acute complications like DKA. This is applicable for BOTH type I and II diabetes patients: [Ref]
| ALL diabetic patients |
|
| Patients who take insulin | NEVER stop insulin
|
| Patients who take oral medications | Most oral drugs are typically temporarily stopped during acute illness and restarted once the person is feeling better + eating and drinking for 24-28 hours
Not directly relevant, other medications like ACE inhibitors, ARBs, diuretics, NSAIDs should also be stopped to reduce the risk of AKI (if there is a risk of dehydration) |
Patient should seek medical advice for potential hospital admission if:
- ↑ Ketone levels (urine ketone >2+ or blood ketones > 3 mmol/L)
- Persistent vomiting (>2 hours)
- Unable to keep oral fluids down
- Signs of severe dehydration
- Hypoglycaemia (unable to maintain blood glucose >3.9 mmol/L)
It is important to advise T1DM patients about cautious alcohol intake. Alcohol can initially raise blood sugar, but can later cause hypoglycaemia and trigger DKA.
Blood Glucose Monitoring
Each T1DM patient should undergo both of the following monitoring approaches.
Blood Test – HbA1c
Measure HbA1c every 3-6 months.
HbA1c target: ≤48 mmol/mol (6.5%)
Note that although HbA1c is not helpful in diagnosing T1DM, but it’s helpful to monitor blood glucose levels in T1DM.
Self-Monitoring
1st line: continuous glucose monitoring (real-time or intermittently scanned)
2nd line (if the person cannot use or does not want continuous glucose monitoring): capillary blood glucose self-monitoring (finger prick)
- Measure at least 4 times a day (including before each meal and before bed)
- Blood glucose targets:
- 5-7 mmol/L on waking
- 4-9 mmol/L at other times (4-7 mmol/L before meals, and 4-9 mmol/L after meals)
Pharmacological Management
Approach:
- Definitive management of T1DM is insulin therapy – ALL patients with T1DM require insulin treatment
- Consider adding metformin to insulin if BMI ≥25 kg/m2 (or ≥23 kg/m2 for those from South Asian and related family background)
Insulin Therapy
1st line: MDI basal-bolus insulin regimen
- Basal: long or ultra-long acting insulin given at the same time, same dose every day
- 1st line: twice-daily detemir
- 2nd line: once-daily glargine
- If there are concerns regarding nocturnal hypoglycaemia: once-daily degludec
- Bolus: rapid-acting insulin given before each main meal, dose varies (based on carbohydrate intake and current glucose level)
- Examples include lispro, aspart
2nd line: twice-daily mixed insulin regimen
Insulin injection technique:
- Subcutaneous injection
- 90-degree needle angle (this is due to very short needles)
Insulin injection sites:
- Abdomen (preferred) – absorbed fastest and most predictably
- Thighs
- Upper arms
- Upper outer buttocks
Monitoring
Children and young people with T1DM should be monitored for:
- Thyroid disease (yearly at diagnosis, until transfer to adult services)
- Diabetic kidney disease (yearly from 12 y/o onwards)
- Monitor with first morning sample to measure urine ACR
- Hypertension (yearly from 12 y/o onwards)
- Diabetic retinopathy (yearly from 12 y/o onwards)
- Coeliac disease testing (one-off)
Diabetes Complications
Screening and Management
| Complication | Screening Method | Frequency |
|---|---|---|
| Diabetic retinopathy | Retinal photography or eye examination | Annually from diagnosis (T2DM) or 5 years after diagnosis (T1DM) |
| Diabetic nephropathy (CKD) | Urine albumin-to-creatinine ratio (ACR), serum creatinine / eGFR | Annually |
| Peripheral neuropathy | Foot examination, including sensory tests | At least annually |
| Peripheral vascular disease | Foot pulses and ulcer risk assessment | |
| Blood pressure monitoring | HBPM / ABPM preferred | |
| Lipid profile | Blood test (cholesterol, LDL, triglycerides) | |
| Weight / BMI monitoring | Clinical measurement | |
| Smoking status | Patient enquiry/clinical documentation |
Also see the following articles and specific management aspects:
Hypoglycaemia in T1DM
Hypoglycaemia Management
Able to swallow → fast-acting form of glucose
Decreased level of consciousness (thus cannot safely take oral treatment) →
- No IV access → IM glucagon
- With IV access → IV glucose
- Give oral carbohydrate when safe to swallow
Impaired Hypoglycaemia Awareness
- Assess at each annual review
- Use the Gold Score / Clarke score to quantify hypoglycaemia awareness
Management:
- AVOID relaxing blood glucose targets
- Educate on avoiding and treating hypoglycaemia (see above)
- Consider
- Insulin pump
- Real-time continuous glucose monitoring (if not already using)
Blood Glucose Control in Hospital
Target: 5-8 mmol/L
IV insulin should be used (instead of subcutaneous insulin) if ANY of the following:
- Unable to eat
- Predicted to miss >1 meal
- Presence of an acute situation to result in unpredictable blood glucose levels (e.g. major surgery, high-dose steroid treatment, inotrope treatment, sepsis)
- Unpredictable insulin absorption (e.g. circulatory compromise)
DVLA and Diabetes Mellitus
The DVLA guidance on diabetes driving applies to both type 1 and 2 diabetes.
The guidance and restrictions mainly centre around insulin treatment and the occurrence of hypoglycemic episodes, therefore, it is more often applicable to those with T1DM.
When to Notify the DVLA
Inform the DVLA if:
- Diabetes treated with insulin (type 1 / 2) – a must for all patients
- Consider if taking medications that can cause hypoglycaemia (e.g. sulfonylurea)
When to Stop Driving
Situations to stop driving IMMEDIATELY and notify the DVLA if:
- >1 episode of severe hypoglycaemia while awake in the past 12 months
- Any episode of severe hypoglycaemia while driving
- Patient developed impaired awareness of hypoglycaemia
- Visual / peripheral sensation impairment that impairs driving
Starting insulin for less than 3 months may temporarily bar driving, pending medical advice and DVLA notification.
Blood Glucose Monitoring Requirement
For group 1 drivers (car or motorcycle):
- Check blood glucose at least twice daily on days the person drives
- Check blood glucose just before driving and at intervals no longer than two hours when driving longer journeys
For group 2 drivers (bus, lorry etc.):
- Check blood glucose at least twice daily on both driving and non-driving days
- Must provide 6 weeks of uninterrupted blood glucose records for annual license review
References