Unwell Person on Insulin Algorithm

The full reasoning pathway — in any unwell insulin-treated patient, measure glucose AND ketones first; the ketone level (not the glucose) decides DKA risk. Never omit insulin, support fluids/carbs, and admit early.StartDecisionInvestigateActionReferStop / Admit

PresentationUnwell patient on insulin

Any intercurrent illness (infection, D&V, MI, missed insulin) in a person on insulin. Stress hormones drive glucose and ketones up — insulin needs usually rise even if eating less.

Step 2 · Investigate — same minuteCapillary glucose + blood ketones

Measure both. The ketone level, not the glucose, defines DKA risk. On an SGLT2 inhibitor, glucose can be near-normal with significant ketosis (euglycaemic DKA).

Step 1 · Safety — DKA?Ketones high / vomiting / drowsy / can't cope?

Blood ketones ≥3 (or urine 2+), vomiting unable to keep fluids down, abdominal pain, deep rapid (Kussmaul) breathing, drowsiness/confusion, dehydration, NEWS2 ≥5.

YES

Stop · Admit999 — suspected DKA

Emergency admission for IV fluids + fixed-rate insulin. Continue basal insulin; do not delay transfer.

NO — home management

Step 7 · ActionSick-day insulin rules

Never stop insulin; monitor glucose 2–4 hourly; recheck ketones; give correction doses; maintain fluids/carbs.

Step 7 · adjust by ketone level

Ketones <0.6

Usual insulin + fluids

Continue normal insulin, hydrate, recheck glucose/ketones, treat the underlying illness.

Ketones 0.6–1.5

Extra fluids + recheck

Increase fluids, give correction insulin per plan, recheck in 2 h; seek advice if not settling.

Ketones ≥1.5–3

Correction + urgent advice

Extra rapid-acting insulin now, fluids; contact diabetes team/same-day. ≥3 → emergency.

Step 6 · ReferEscalation

999 / same-day DKA, ketones ≥3, persistent vomiting, drowsiness, or failing home management. Diabetes team for advice on correction dosing or recurrent decompensation.

Step 8 · Prevention & self-managementSick-day kit + written plan

Ensure a blood-ketone meter + strips, a personalised correction-dose plan, glucagon for hypos, and clear advice: never omit insulin, check ketones when unwell or glucose >13–15, stop SGLT2 inhibitors during illness.

Step 9 · Safety-netWhen to call for help

999 / same-day if vomiting and can't keep fluids down, ketones rising despite insulin, drowsy/confused, deep rapid breathing, or abdominal pain.

⚠️ Measure ketones, not just glucose — DKA is defined by ketones and acidosis, and on SGLT2 inhibitors the glucose can be normal. Never omit insulin during illness, even if the person is eating less.

Safety

Red Flags — Recognising Diabetic Ketoacidosis

Done

DKA is the emergency you are trying to prevent in any unwell insulin-treated patient. It can develop within hours and is defined by ketones and acidosis — not by how high the glucose is.

Blood ketones ≥3 mmol/L (or urine ketones 2+/++) Established or imminent DKA. → 999. Continue insulin; IV fluids + fixed-rate insulin in hospital.

Vomiting + unable to keep fluids down Cannot follow oral sick-day rules; dehydration and ketosis worsen fast. → Same-day/admit.

Deep, sighing (Kussmaul) breathing, fruity breath, abdominal pain Acidosis. → 999.

Drowsiness, confusion, reduced consciousness Severe DKA or HHS. → 999.

Near-normal glucose but unwell + ketones, on an SGLT2 inhibitor Euglycaemic DKA — easily missed. Check ketones in everyone unwell on these drugs; stop the SGLT2 inhibitor. → Same-day/999 per ketones.

Signs of the precipitant Sepsis (NEWS2 ≥5), chest pain (MI can precipitate DKA), or a surgical abdomen — treat the cause alongside the DKA.

DKA arises from absolute or relative insulin deficiency: without enough insulin, cells cannot use glucose, the body burns fat, and ketoacids accumulate, producing acidosis, osmotic diuresis and dehydration. Because illness raises insulin requirements, the same insulin dose that was adequate when well becomes "relatively deficient" — which is why DKA can occur even in someone who has not missed a dose, and why ketone monitoring (the direct marker of the process) outperforms glucose for early detection.

Diagnose

Assess — Glucose AND Ketones, Plus the Precipitant

Done

In any unwell insulin-treated patient, measure capillary glucose and blood ketones the same minute — and look for what made them unwell.

Blood ketones

The key test. <0.6 normal · 0.6–1.5 mild (recheck/fluids) · 1.5–3 significant (correction insulin + advice) · >3 emergency.

Capillary glucose

Usually high, but can be normal in euglycaemic DKA (SGLT2 inhibitors, pregnancy, reduced intake). Do not be reassured by a normal glucose.

Hydration / obs

Pulse, BP (postural), capillary refill, urine output, NEWS2. Dehydration accelerates deterioration.

Find the precipitant

Infection (UTI, chest, skin/foot), missed/insufficient insulin, pump failure, MI, pancreatitis, new diagnosis, alcohol. Treat it alongside.

If admitting

Hospital will add venous gas/bicarbonate, U&E, FBC, CRP, cultures — but do not delay referral to obtain these in the community.

Measuring ketones converts management from guesswork into an algorithm: the ketone level directly grades DKA risk and dictates how much extra insulin and fluid is needed. Identifying the precipitant matters because DKA rarely resolves until its cause is treated — a missed pneumonia or silent MI will keep driving ketogenesis despite insulin.

Diagnose

Which Decompensation? DKA vs HHS vs Hypoglycaemia

Done

An unwell insulin-treated patient can decompensate in three different directions — and the management of each diverges sharply. The glucose, ketones and conscious level separate them.

DKA

Usually T1DM (or any patient on an SGLT2 inhibitor). Ketones ≥3 + acidosis; glucose often >11 but can be normal (euglycaemic). Develops over hours. → insulin + fluids, treat the precipitant.

HHS

Older T2DM. Very high glucose (often >30), marked dehydration / hyperosmolarity, drowsy, minimal ketones, no significant acidosis. Develops over days. → cautious fluids first, lower-dose insulin, higher mortality than DKA.

Hypoglycaemia

Glucose <4 with poor intake but continued insulin/sulfonylurea. Treat with fast-acting carbohydrate ± glucagon; do not stop basal insulin, adjust per plan.

Why it matters

HHS is corrected more slowly and fluid-led, unlike DKA — mislabelling risks harm. Euglycaemic DKA blurs the picture, so always check ketones regardless of glucose.

DKA and HHS sit at opposite ends of a spectrum of insulin deficiency: DKA is the acute, ketoacidotic emergency of near-total insulin lack, whereas HHS is the slower, profoundly dehydrated, hyperosmolar state of relative insulin deficiency in type 2 diabetes — and because HHS fluid shifts are large, correction must be slower and more cautious than in DKA. Hypoglycaemia is the mirror-image emergency in the unwell patient who keeps taking insulin while not eating. Naming which one you are dealing with dictates the whole treatment, which is why it is a high-yield discriminator.

Treat

The Golden Rule — Never Omit Insulin

Done

The single most important action — and the commonest mistake patients make is stopping insulin because they are eating less.

Continue basal insulin

Always — even if not eating. The body still needs background insulin to suppress ketogenesis.

Monitor more

Glucose every 2–4 hours (and overnight if unwell); recheck ketones regularly.

Correction doses

Give extra rapid-acting insulin per the individual's sick-day plan (commonly ~10–20% of total daily dose) when glucose/ketones are high; recheck in 2 h and repeat as needed.

Insulin pump users

If ketones rising, give correction by pen/syringe (assume pump/cannula failure), check the set, and follow pump sick-day guidance.

SGLT2 inhibitors

Stop during the illness (euglycaemic DKA risk); restart when fully recovered and eating/drinking.

Stopping insulin during illness removes the only brake on ketogenesis and is the leading avoidable precipitant of DKA admissions. Counter-intuitively, the person who is eating less often needs more insulin, not less, because illness-related counter-regulatory hormones dominate. Teaching "never stop insulin, give correction doses, check ketones" is the highest-yield safety message.

Treat

Ketone-Led Home Management & Fluids

Done

<0.6

Normal. Continue usual insulin, hydrate, treat the illness, keep monitoring.

0.6–1.5

Mild ketosis. Extra fluids, give a correction dose per plan, recheck glucose & ketones in 2 h.

1.5–3.0

Significant. Repeat correction insulin, push fluids, contact diabetes team / seek same-day advice. If not falling → admit.

>3.0

Emergency — treat as DKA. 999. Continue insulin; IV management in hospital.

Fluids

Sip regularly, aim ~3 L/day. If glucose high → sugar-free fluids. If glucose normal/low and not eating → sugary fluids to maintain carbohydrate.

Hypoglycaemia

If glucose low (poor intake + insulin), treat with fast-acting carbohydrate; have glucagon available. Do not stop basal insulin — adjust per plan.

The ketone level provides a simple, graded action plan that patients and clinicians can follow at home, catching deterioration early. Fluid and carbohydrate replacement counters the osmotic diuresis and starvation ketosis that accompany illness, while correction insulin shuts down ketogenesis.

Refer

When to Admit or Get Specialist Advice

Done

999 / same-day

Blood ketones ≥3, vomiting unable to keep fluids down, drowsiness/confusion, Kussmaul breathing, severe dehydration, or ketones not falling despite correction doses.

Diabetes team advice

Ketones 1.5–3 not settling, uncertainty about correction dosing, pump problems, or recurrent sick-day decompensation.

Manage at home

Alert, tolerating fluids, ketones controlled and falling, has a plan and can seek help — with explicit safety-netting.

The decision to admit is driven by ketone trajectory and the ability to take oral fluids, not the absolute glucose. Early admission of a patient whose ketones are not falling prevents progression to severe, dangerous DKA.

Lifestyle

Prevention — The Sick-Day Kit & Education

Done

Blood-ketone meter + strips Every insulin-treated patient should have one and know the action thresholds.

Personalised correction plan Agreed with the diabetes team — how much extra insulin, how often, when to seek help.

Never-omit-insulin message Reinforced at every review and after any DKA admission.

Stop SGLT2i when ill Clear written instruction for anyone on these drugs.

Glucagon & hypo plan For the flip-side risk of hypoglycaemia with poor intake.

Vaccination & foot/skin care Reduce the infections that precipitate DKA.

Most DKA admissions in established diabetes are precipitated by illness plus inadequate sick-day self-management. Equipping patients with ketone testing, a written correction plan and the never-omit-insulin rule before they become unwell is the single most effective prevention strategy.

Safety

Safety-Netting — What to Tell the Patient

Done

999 if

Vomiting and can't keep fluids down, blood ketones ≥3, drowsy/confused, deep rapid breathing, severe abdominal pain, or collapse.

Same-day if

Ketones rising despite extra insulin, glucose persistently very high, reduced urine output, or feeling steadily worse.

Keep doing

Taking insulin, checking glucose 2–4 hourly and ketones, sipping fluids, treating the underlying illness.

Clear, specific safety-netting — given verbally and in writing — is what allows safe home management. The patient must leave knowing the exact thresholds (ketones ≥3, can't keep fluids down) that mean "call 999 now", and that they must never stop their insulin.

Diagnose

After the Illness — Review & Learn

Done

Restart held drugs

Resume SGLT2 inhibitor and any held SADMAN drugs once fully recovered and eating/drinking normally; reconcile the medication list.

Review the trigger

Treat/complete management of the precipitating infection; consider why DKA risk arose (technique, pump, education gaps).

Reinforce sick-day rules

Use the episode to revisit ketone testing, correction dosing and the never-omit-insulin rule; update the written plan.

Recurrent DKA

Refer to the diabetes team / psychology — recurrent DKA may reflect insulin omission, distress, eating disorder or social factors.

Every illness episode is a teaching opportunity and a chance to catch the medicines-safety pitfall of held drugs not being restarted. Recurrent DKA in particular is a red flag for an underlying behavioural, psychological or social driver that needs specialist support, not just repeated acute treatment.