01Purpose and principlesWhat the treatment does and how it fits into care.
Insulin replacement has three jobs: basal suppression of hepatic glucose release, prandial coverage of carbohydrate and correction of unexpected hyperglycaemia. One preparation can serve more than one role in a mixed regimen, but its action profile must match meals and monitoring.
The central decision is which regimen the person can use safely while meeting their goals. Flexibility, dexterity, vision, cognition, work, food predictability, hypoglycaemia awareness, kidney function and access to trained carers matter as much as HbA1c.
Titration is pattern management. A single reading can reflect food, stress, sensor lag or injection error; at least several comparable days are usually needed unless an immediate low, ketosis or severe symptom requires urgent change.
Key points
- Rapid-acting analogues cover meals and corrections; short-acting human insulin has slower onset and longer meal-related action, so timing is not interchangeable.
- Intermediate NPH and long- or ultra-long analogues provide basal insulin; basal controls fasting hepatic glucose output and must not be used repeatedly to correct post-meal excursions.
- Basal–bolus multiple daily injection is the standard flexible regimen for most adults with type 1 diabetes; pump and hybrid closed-loop options require structured training and backup plans.
- In type 2 diabetes, start insulin when symptomatic or catabolic hyperglycaemia demands it or when agreed targets remain unmet; a basal regimen is often the simplest entry point.
- Titrate basal insulin from repeated fasting patterns, mealtime insulin from the corresponding post-meal or next-premeal pattern, and corrections from an individually derived sensitivity factor.
- Recurrent overnight hypoglycaemia with high morning glucose may reflect rebound, basal excess or late food; examine overnight data rather than increasing insulin automatically.
- Lipohypertrophy, repeated sites, poor mixing of cloudy insulin, storage damage and needle or cannula problems produce erratic glucose and mimic an incorrect dose.
- Prescribe insulin by brand, concentration, device and dose in full units; never abbreviate units to U or IU, and never withdraw concentrated insulin from a pen with a syringe.
- Insulin detemir supply is expected to end in the UK in December 2026; transition must follow current ABCD guidance with individual dose review, not unit-for-unit assumption.
02Indications, selection and cautionsWho may benefit, who needs urgent treatment and important alternatives.
Falling glucose overnight or between meals, recurrent fasting lows and a need to snack without hunger suggest basal dose exceeds background requirement, especially after weight or renal change.
Repeated fasting rise without bedtime carbohydrate, missed dose or overnight hypoglycaemia suggests inadequate basal coverage; check technique and timing before increasing.
Post-meal peaks followed by later lows can reflect bolus given too late, inaccurate carbohydrate estimation or an insulin whose action outlasts absorption rather than simply too little insulin.
Unexplained rising glucose and ketones in a pump user can progress quickly because only rapid-acting insulin is present. Inspect cannula, tubing, reservoir and infusion site and use the emergency backup plan.
Rubbery thickened injection areas, repeated comfortable sites and highly variable absorption indicate local tissue change. Moving suddenly to healthy skin can lower requirements and provoke hypoglycaemia.
Confusion, seizure, loss of consciousness or need for another person's help requires rescue treatment, emergency assessment when indicated and urgent regimen, awareness and driving review.
A new pen colour, unfamiliar concentration, missing meal dose or accidental rapid-acting injection instead of basal can cause prolonged harm; identify exact product and time immediately.
03Assessment before treatmentTests and checks that guide safe selection.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Structured glucose or CGM downloadFirst step - Why
- Link fasting, meals, exercise and overnight patterns to each insulin component.
- Interpretation and limitations
- Check data completeness, insulin timing, carbohydrate and activity annotations and time below range first. Change the insulin responsible for the pattern, not whichever dose is easiest to alter.
- 02
Capillary glucose and blood ketones - Why
- Assess acute hyperglycaemia, pump failure and illness safely.
- Interpretation and limitations
- Rising ketones indicate insufficient effective insulin regardless of the apparent prescribed dose. Follow the written correction and backup-injection plan and seek urgent care at the specified threshold.
- 03
Observed injection or device technique - Why
- Find errors in priming, dialling, mixing, site rotation, cannula insertion and dose delivery.
- Interpretation and limitations
- Ask the person to demonstrate with their own device. Confirm needle change, dwell time, cloudy insulin resuspension, pump set change and that concentrated insulin is used only with its intended device.
- 04
Injection-site examination - Why
- Detect lipohypertrophy, lipoatrophy, infection or repeated trauma.
- Interpretation and limitations
- Avoid abnormal areas and create a rotation map. Anticipate increased absorption and reduce dose with close monitoring when moving from lipohypertrophy to normal tissue.
- 05
HbA1c and time-in-range metrics - Why
- Measure longer-term effectiveness without losing sight of hypoglycaemia.
- Interpretation and limitations
- A lower HbA1c does not justify severe lows. Review variability and time below range; altered red-cell turnover can make HbA1c discordant from the glucose profile.
- 06
Renal function and weight trend - Why
- Identify falling insulin clearance or changing metabolic requirement.
- Interpretation and limitations
- Kidney decline and weight loss commonly reduce dose needs, whereas steroids, infection and weight gain may increase them. Reassess after dialysis or major nutritional change.
- 07
Insulin prescription and storage audit - Why
- Prevent brand, concentration, device and potency errors.
- Interpretation and limitations
- Verify every transition record, current pen and pharmacy supply. Heat, freezing and use beyond in-use limits can reduce effect; follow product-specific storage rather than generic refrigeration advice.
04Treatment approachPreparation, options, escalation and aftercare.
01Type 1Basal–bolus or pump replacementFirst stepConfirmed insulin-deficient type 1 diabetes requiring lifelong insulin.+
- 1Offer structured education and multiple daily basal–bolus injections using analogue insulin, or assess pump and hybrid closed-loop eligibility and preference through the specialist service.
- 2Teach carbohydrate ratios, correction sensitivity, active insulin, injection or infusion technique, ketone rules, hypoglycaemia, exercise, alcohol, driving and backup supplies.
- 3Titrate components from reproducible patterns while protecting basal coverage; a pump user needs written doses and available pens for immediate conversion if delivery fails.
- 4EscalationReview severe hypoglycaemia, recurrent ketones, high variability or treatment distress promptly and escalate technology or psychological support rather than blaming the user.
02Type 2Start basal insulinSymptomatic or catabolic hyperglycaemia, or persistent above-target glucose despite appropriate non-insulin treatment.+
- 1Address symptoms and ketones urgently, explain why insulin is being used, agree the target and provide injection, monitoring, hypoglycaemia, driving and sick-day education before initiation.
- 2Select NPH or a long-acting analogue under NICE criteria, start at the locally approved individual dose and titrate from several fasting readings using a written algorithm.
- 3Review sulfonylurea, SGLT2 and other co-therapy for hypoglycaemia or DKA risk while retaining medicines with independent cardiorenal benefit when appropriate.
- 4If fasting glucose reaches target but HbA1c remains high, examine meals and add prandial or mixed insulin rather than increasing basal into overnight hypoglycaemia.
03PatternSafe dose titrationRepeated glucose outside the agreed range without an acute emergency.+
- 1Confirm the pattern on comparable days and annotate meals, dose timing, active insulin, activity, alcohol, illness, steroids, menstruation and injection site.
- 2Identify which insulin action window overlaps the problem: background basal, a named meal bolus, correction factor or mixed-insulin component.
- 3Make one modest protocol-based change, set boundaries against stacking and arrange enough monitoring to observe both intended response and delayed hypoglycaemia.
- 4Reassess after the agreed number of days or sooner for lows, ketones or symptoms; reverse unsafe change and seek specialist help when patterns remain contradictory.
04ErrorWrong insulin or doseKnown or suspected product, concentration, timing or administration mistake.+
- 1Identify exact insulin, concentration, intended and actual dose, time, glucose, food and whether another dose was omitted; contact emergency or poisons advice according to risk.
- 2Begin frequent glucose monitoring for the full potential action period, ensure rapid carbohydrate and supervised access, and check ketones if essential insulin was missed.
- 3Treat hypoglycaemia promptly and recognise that long-acting or sulfonylurea co-exposure can cause recurrence requiring hospital observation.
- 4After safety is secured, correct prescribing and storage systems, report the incident and use human-factors review rather than relying on a warning to be more careful.
05Regimens, contraindications and interactionsTreatment details and the circumstances that modify them.
Rapid-acting insulin analogue
Dose before or with meals using the trained carbohydrate ratio and correction plan.Timing and duration vary by product; avoid correction stacking, confirm dose during poor intake and keep basal insulin. Pump interruption can cause rapid ketosis.
Long-acting basal insulin analogue
Give once or twice daily at the individually titrated consistent time.Do not use for meal correction. Renal decline, weight loss or movement from lipohypertrophy may lower need; concentrated products require exact device and brand prescribing.
Human isophane NPH insulin
Use once or twice daily and titrate from fasting and overnight patterns.Has a pronounced peak and greater nocturnal hypoglycaemia potential in some people. Resuspend cloudy insulin correctly and align meals and monitoring with its profile.
Biphasic premixed insulin
Give at fixed meal-related times with dose split determined by the diabetes plan.Less flexible for variable food or shifts; omitted meals cause hypoglycaemia and independent component titration is impossible. Confirm the exact mix and timing.
Glucagon rescue
Administer the prescribed rescue device when severe hypoglycaemia prevents safe swallowing.May be less effective after fasting or alcohol. Recovery requires carbohydrate, supervision and urgent review of insulin, awareness, renal function and driving.
06Complications, monitoring and follow-upAdverse effects, response and longer-term review.
- Review fasting, meal-linked, overnight and exercise glucose patterns with insulin timing and active dose; change only the component plausibly responsible.
- Ask about every hypoglycaemic episode, awareness, rescue treatment, driving and fear, and prioritise eliminating severe or nocturnal lows before lowering HbA1c further.
- Inspect injection and infusion sites and observe technique at least annually and whenever glucose becomes erratic, a device changes or doses rise unexpectedly.
- Track weight, renal function, food intake, steroids and activity because each can change insulin need more quickly than routine review schedules.
- Audit prescriptions by exact brand, concentration, device and full-word units at transitions of care, especially when concentrated insulin or detemir replacement is involved.
07Special situationsVariants, exceptions and circumstances that change the usual approach.
Fasting guides basal
When fasting is consistently in range but daytime HbA1c remains high, more basal is unlikely to solve meal excursions and may create nocturnal hypoglycaemia.
Sites alter dose delivery
Insulin enters unpredictably from lipohypertrophy. The same numerical dose can act much more strongly after moving to healthy skin, so planned reduction and monitoring are prudent.
Pumps contain no depot
Most pumps deliver only rapid-acting insulin; an occlusion therefore removes basal delivery as well as bolus capacity, allowing ketones to rise within hours.
Concentrated means device specific
The pen displays units designed for that formulation. Syringe extraction or mental conversion introduces large errors and must never be normal practice.
Detemir transition is active care
With supply expected to end in December 2026, each user needs an alternative chosen for pregnancy, hypoglycaemia, timing and dose—not an automatic electronic switch.
Insulin is not failure
Beta-cell decline is part of type 2 diabetes biology. Framing insulin as punishment delays effective therapy and increases catabolic and emergency presentations.
08Common pitfallsFrequent interpretation and management errors.
- 01
Increasing basal insulin to treat post-meal hyperglycaemia after fasting is already on target.
- 02
Writing U or IU instead of units on an insulin prescription.
- 03
Withdrawing concentrated insulin from a pen with a syringe.
- 04
Failing to inspect injection sites when glucose becomes highly variable.
- 05
Leaving a pump user without rapid access to backup injection insulin.
- 06
Switching insulin detemir unit for unit without current specialist or ABCD guidance.