Sick Day Management of T1DM

For adults with type 1 diabetes during intercurrent illness — companion to Type 1 diabetes (routine care and insulin pump failure) and DKA & HHS (the emergencies this pathway aims to prevent). For type 2 diabetes, see Sick Day Management of T2DM.

Refer for emergency assessment if

• Persistent hyperglycaemia — BGL >15 mmol/L for more than 4–6 hours and clinically unwell.
• High ketones unresponsive to initial management — moderate/large on urine testing, or >1.5 mmol/L on blood.
• Significant dehydration or recurrent vomiting for >4 hours.
• Pregnant, with random BGL >10 mmol/L and/or blood ketones ≥0.6 mmol/L, or persistent BGL <3.5 mmol/L — seek urgent obstetric/endocrinology advice or refer to ED.
• Severe hypoglycaemia requiring third-party assistance, including any loss of consciousness.
• An acute, severe diabetes-related end-organ complication.

Why illness destabilises control

Insulin requirements typically increase with acute illness (fever, infection) even when oral intake is poor — because infection itself drives insulin resistance. Vomiting/diarrhoea illnesses can lower glucose but also raise the risk of euglycaemic ketoacidosis (ketosis/acidosis with normal or only mildly raised glucose) — a trap, because a reassuring glucose reading does not exclude significant ketosis. See DKA & HHS for the full differentiation of DKA, euglycaemic DKA and HHS.

A related trap at the other end of the illness: some people may first present with type 1 diabetes during an accompanying viral illness, with symptoms of diabetic ketoacidosis hidden by or mistakenly attributed to viral symptoms — a finger-prick BGL is cheap and quick where DKA could plausibly be masquerading as gastro or flu in someone not already known to have diabetes.

Ketone testing

Blood ketone testing is preferred over urine (more accurate, faster warning of ketosis, and avoids urine testing’s practical downsides).

Blood ketones (mmol/L)	Urine ketones	Interpretation
<0.6	Negative	Normal
0.6–1.5	Trace/small	Increased ketone production
1.5–3.0	Moderate	Impending DKA
>3.0	Large	Probable DKA

Insulin adjustment

• Never withhold or stop basal insulin — the single biggest DKA-prevention rule, regardless of reduced oral intake.
• Total insulin requirement typically increases in acute illness; a reduction may be needed specifically with gastrointestinal illness.
• Supplemental doses of rapid-acting insulin (not short-acting — it has a longer duration and is slower to act) if BGL is above target and/or ketones are present: usually 5–20% of the total daily dose, given ≥2 hours after the last rapid-acting dose (usually between meals), following the patient’s own action plan.
• If vomiting occurs after a bolus dose has already been given, sip glucose-containing fluid every 20–30 minutes while monitoring glucose closely.
• Some guidance frames this the same way from the insulin side: for type 1 diabetes, supplemental doses of rapid-acting insulin every 2–4 hours if BGL remains elevated is a reasonable default; if two supplemental doses in a row bring no improvement in BGL or ketones, that itself is the trigger to seek medical review rather than giving a third dose unsupervised.
• If unsure how to adjust insulin, seek urgent diabetes specialist advice or refer to ED.

Insulin pump users

Pump-specific sick-day advice, on top of everything above (the same never-withhold-basal-insulin and supplemental-dose principles apply — a pump just delivers both as rapid-acting insulin rather than a separate long-acting injection):

• A temporary basal rate increase is usually needed in acute illness for the same insulin-resistance reasons as multiple-daily-injection dosing; a temporary reduction is occasionally needed instead if oral intake is significantly reduced.
• An unexplained high glucose reading — even one that isn’t obviously explained by a pump malfunction — still warrants a blood ketone check. If moderately elevated (>0.4 mmol/L), give a corrective dose of rapid-acting insulin by injection, not via the pump, then change the infusion set and line before resuming pump delivery — the corrective response itself covers the case where the line has quietly failed.
• If ketones are more significantly elevated (>1.6 mmol/L) or the patient is nauseated and vomiting, refer to ED. Otherwise, check glucose and ketones hourly and manage further in conjunction with the patient’s diabetes specialist team.
• A disconnected pump only ever held rapid-acting insulin — insulin activity falls to zero within 4–6 hours of disconnection, with a real risk of ketoacidosis if the pump cannot be promptly reconnected. A pump user’s sick day kit therefore needs backup rapid- and long-acting insulin pens and needles, not just spare pump consumables, in case the pump fails outright and injections are needed until it can be replaced. See Type 1 diabetes’s insulin pump failure section for the full pump-malfunction workup.

Fluid and carbohydrate intake

Maintain hydration and carbohydrate intake together — ketones need insulin to clear, and insulin cannot be safely given if glucose is low, so err toward adequate glucose intake.

• Try to eat normally; if not, aim for 15 g carbohydrate/hour during waking hours from easy-to-digest food (dry toast, plain rice, dry biscuits, custard).
• Aim for 125–250 mL (half–one cup) of fluid every hour: carbohydrate- containing (juice, regular soft drink/cordial, sports drink, sweetened tea or milk) if BGL <15 mmol/L; carbohydrate-free (water, diet drinks, plain tea) if BGL >15 mmol/L.
• Avoid excess caffeine — a gastric irritant that can worsen nausea.
• With vomiting/diarrhoea: oral rehydration solutions (gastrolyte/hydralyte) are relatively low in carbohydrate, so extra carbohydrate may still be needed; dilute sweetened or hypertonic fluids for better tolerance; sip slowly; let carbonated drinks go flat first.

Escalate to emergency department if

• BGL remains <4.0 mmol/L after two hypoglycaemia treatments.
• Blood ketones >3.0 mmol/L (or large on urine).
• After 2 supplemental insulin doses, BGL/ketones are still rising or not falling, or BGL remains >15 mmol/L and/or ketones remain >1.5 mmol/L (blood)/moderate-large (urine).
• The patient or their support person feels unable to manage the situation.

Medications to review

With significant vomiting/diarrhoea, consider withholding diuretics, ACE inhibitors/ARBs, and NSAIDs — the risk being acute kidney injury on top of illness-related dehydration. Metformin and SGLT2 inhibitors carry the same withhold-during-significant-vomiting/diarrhoea logic where a patient with type 1 diabetes happens to be taking one as adjunct therapy; SGLT2 inhibitors specifically add a euglycaemic-ketoacidosis risk on top of the dehydration risk (see “Why illness destabilises control” above), so have a lower threshold to check ketones in anyone on one. Corticosteroids increase insulin requirements rather than needing to be withheld — ask about complementary/alternative medicines too.

Sick day plan and kit

Every patient should leave with (or already have) a written, individualised sick day plan — multiple-daily-injection and insulin-pump plans differ — developed with their GP or credentialed diabetes educator, and reviewed after any change in diabetes treatment, a hospital admission, pregnancy, relocation, or travel. A sick day kit should hold: a copy of the plan, a blood glucose/ketone meter with in-date strips, a glucose diary, a thermometer, analgesia, hypoglycaemia treatment including in-date glucagon, spare pens/needles or pump consumables (pump users specifically need backup long-acting insulin too, not just rapid-acting pump consumables, in case the pump itself fails), and relevant phone numbers — check it every 3 months.