Type 2 Diabetes in Primary Care: From Diagnosis to Insulin Initiation
A practical, evidence-based framework for managing T2DM in the GP setting
Type 2 diabetes affects over 537 million adults globally. This guide covers the complete GP management pathway — from HbA1c-based diagnosis and lifestyle intervention through metformin initiation, SGLT2 inhibitors, GLP-1 agonists, and insulin initiation protocols.
Clinical Decision Support: This article is for educational purposes and supports — not replaces — clinical judgment. Always verify with current national guidelines, BNF, and specialist consultation when needed.
Type 2 diabetes mellitus (T2DM) is one of the most prevalent and consequential conditions managed in primary care. With over 537 million adults affected globally and projections suggesting this will rise to 783 million by 2045, GPs are at the frontline of both prevention and management. The landscape of T2DM pharmacotherapy has transformed dramatically over the past decade, with SGLT2 inhibitors and GLP-1 receptor agonists now offering cardiovascular and renal protection beyond glucose lowering.
Diagnosis: HbA1c and Fasting Glucose Criteria
| Test | Diabetes | Pre-diabetes (IFG/IGT) | Normal |
|---|---|---|---|
| HbA1c | ≥48 mmol/mol (6.5%) | 42–47 mmol/mol (6.0–6.4%) | <42 mmol/mol (<6.0%) |
| Fasting plasma glucose | ≥7.0 mmol/L | 6.1–6.9 mmol/L (IFG) | <6.1 mmol/L |
| 2-hour OGTT glucose | ≥11.1 mmol/L | 7.8–11.0 mmol/L (IGT) | <7.8 mmol/L |
| Random plasma glucose | ≥11.1 mmol/L + symptoms | N/A | N/A |
A single HbA1c ≥48 mmol/mol is diagnostic in a symptomatic patient. In asymptomatic patients, two separate tests are required. Do not use HbA1c for diagnosis in haemoglobinopathies, haemolytic anaemia, recent blood transfusion, or pregnancy.
HbA1c Targets: Individualised Approach
NICE NG28 recommends individualised HbA1c targets rather than a one-size-fits-all approach. The target should balance glycaemic control against hypoglycaemia risk, patient preference, and comorbidities.
- 48 mmol/mol (6.5%): Target for newly diagnosed T2DM managed with lifestyle alone or metformin
- 53 mmol/mol (7.0%): Target for patients on drugs that can cause hypoglycaemia (sulphonylureas, insulin)
- 58–64 mmol/mol (7.5–8.0%): Consider in frail elderly, limited life expectancy, or recurrent hypoglycaemia
- Avoid HbA1c <48 mmol/mol in patients on insulin or sulphonylureas — hypoglycaemia risk
The Drug Escalation Pathway
Step 1: Metformin — Still the Cornerstone
Metformin remains the first-line pharmacological agent for T2DM in the absence of contraindications. It reduces HbA1c by approximately 11–14 mmol/mol (1–1.5%), is weight-neutral or causes modest weight loss, has a strong cardiovascular safety record (UKPDS), and is inexpensive. Start at 500 mg OD with food and titrate over 4–8 weeks to 1 g BD or 850 mg TDS as tolerated. Modified-release metformin reduces GI side effects.
Metformin is contraindicated when eGFR <30 mL/min/1.73m². Reduce dose to 500 mg BD when eGFR 30–45 mL/min/1.73m². Withhold temporarily before contrast media and for 48 hours after, if eGFR <60.
Step 2: Adding a Second Agent — The SGLT2i/GLP-1 Era
When HbA1c remains above target on metformin alone, the choice of second agent is now guided by cardiovascular and renal comorbidities, not just glucose lowering. NICE NG28 (2022 update) recommends SGLT2 inhibitors or GLP-1 receptor agonists as preferred second-line agents in patients with established cardiovascular disease, heart failure, or CKD.
| Drug Class | Examples | HbA1c Reduction | Weight Effect | Key Benefit | Key Risk |
|---|---|---|---|---|---|
| SGLT2 inhibitor | Empagliflozin, Dapagliflozin, Canagliflozin | 8–11 mmol/mol | −2 to −3 kg | CV/renal protection, HF benefit | DKA, UTI, genital thrush, Fournier's gangrene |
| GLP-1 agonist | Semaglutide, Liraglutide, Dulaglutide | 11–14 mmol/mol | −3 to −5 kg | CV protection, weight loss | Nausea, pancreatitis (rare), injection |
| DPP-4 inhibitor | Sitagliptin, Alogliptin, Saxagliptin | 6–8 mmol/mol | Neutral | Well tolerated, oral | Saxagliptin: HF risk; joint pain |
| Sulphonylurea | Gliclazide MR, Glimepiride | 11–14 mmol/mol | +1 to +2 kg | Inexpensive, effective | Hypoglycaemia, weight gain |
SGLT2 Inhibitors: Practical Prescribing Points
- Do not start if eGFR <45 mL/min/1.73m² (glucose-lowering effect diminished; renal/CV benefit may persist — check individual drug SPC)
- Counsel on genital hygiene to reduce thrush and UTI risk
- Withhold during acute illness, surgery, or prolonged fasting (sick day rules — DKA risk)
- Euglycaemic DKA can occur — check ketones if unwell even with normal glucose
- Dapagliflozin is licensed for HFrEF and CKD independently of diabetes status
Insulin Initiation in Primary Care
Insulin initiation in T2DM is increasingly managed in primary care. The key indication is persistent HbA1c above target despite optimised oral therapy, or symptomatic hyperglycaemia. Most patients with T2DM start with basal insulin (long-acting analogue).
Starting Basal Insulin: The 10-Unit Rule
- Start with 10 units of insulin glargine (Lantus/Toujeo) or insulin detemir (Levemir) at bedtime
- Titrate by 2 units every 3 days until fasting glucose is 4–7 mmol/L
- If fasting glucose <4 mmol/L on two consecutive mornings, reduce dose by 4 units
- Review at 4–6 weeks; if HbA1c still above target, consider adding prandial insulin or switching to premixed
- Refer to diabetes specialist nurse (DSN) for education and injection technique
When initiating insulin, reduce sulphonylurea dose by 50% to reduce hypoglycaemia risk. Stop sulphonylurea once on basal-bolus regimen. Continue metformin and SGLT2i (review SGLT2i if eGFR falls or DKA risk increases).
Annual Diabetes Review: What to Check
- HbA1c, eGFR, urine ACR (albumin:creatinine ratio)
- Blood pressure (target <140/90 mmHg; <130/80 mmHg if CKD/proteinuria)
- Lipid profile — statin therapy for all T2DM patients aged ≥40 or with CVD risk factors
- Foot examination: pulses, sensation (10g monofilament), skin integrity
- Retinal screening (annual digital photography)
- BMI and weight management discussion
- Smoking status and cessation support
- Immunisations: annual flu, pneumococcal, COVID-19 boosters
Key Clinical Takeaways
- Diagnose T2DM with HbA1c ≥48 mmol/mol (two tests if asymptomatic)
- Metformin remains first-line; titrate slowly to minimise GI side effects
- Add SGLT2i or GLP-1 agonist in patients with CVD, HF, or CKD — cardiovascular benefit beyond glucose lowering
- Individualise HbA1c targets: 48 mmol/mol for most; 53 mmol/mol if on hypoglycaemia-risk drugs
- Basal insulin: start 10 units at bedtime, titrate by 2 units every 3 days
- Annual review: HbA1c, eGFR, ACR, BP, lipids, feet, eyes, weight, smoking