Educational draft · awaiting clinical reviewUse Rapid for revision, not patient-care decisions. Check current national and local guidance and the BNF or BNFC before acting.
2 min synopsisUK scopeSources checked 27 Aug 2026Clinical review pending
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Diagnose the emergency before refining diabetes type
Weight loss, vomiting, abdominal pain, deep breathing, dehydration, altered consciousness or acute illness with hyperglycaemia requires immediate glucose, blood ketones and acid-base assessment. Children, pregnant people and anyone with suspected type 1 diabetes can deteriorate rapidly, and an HbA1c request is not an acute safety strategy.
Action: Use ABCDE, capillary glucose and ketones, obtain a venous blood gas and electrolytes, and start the local DKA, HHS or hypoglycaemia pathway when criteria are met. Begin appropriate insulin promptly when type 1 diabetes is clinically likely; do not await autoantibodies, C-peptide or routine outpatient confirmation.
Synopsis
Apply diagnostic glucose and HbA1c criteria correctly, confirm asymptomatic results, recognise when HbA1c is unreliable, and classify urgent presentations safely.
Classic symptoms plus a diagnostic-range venous plasma glucose can establish diabetes; an asymptomatic abnormal result normally needs confirmation on another day.
Diagnostic thresholds are fasting venous plasma glucose at least 7.0 mmol/L, random or two-hour OGTT glucose at least 11.1 mmol/L, or HbA1c at least 48 mmol/mol when valid.
HbA1c 42–47 mmol/mol indicates non-diabetic hyperglycaemia and increased future risk, not established diabetes; offer prevention support and planned reassessment.
Investigation priorities
01
Venous fasting plasma glucoseFirst step
Diagnose dysglycaemia with a standardised measurement after the required fasting interval.
Management branches
AcuteSeparate metabolic emergency from stable diagnosis
A person has hyperglycaemia with illness, weight loss, vomiting, ketotic symptoms or altered consciousness.
Check bedside glucose and blood ketones immediately, then obtain venous gas, electrolytes and hydration observations without waiting for HbA1c.
Start the local DKA or HHS protocol when criteria are met and seek same-day diabetes or paediatric support for possible type 1 diabetes.
ConfirmDiagnose stable dysglycaemia
A person is clinically stable and a screening or symptom-driven test is above the diagnostic threshold.
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.