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OverviewAetiologyPathophysiologyClinical features and red flagsInvestigationsDifferential diagnosisManagementComplicationsMonitoring and follow-upSpecial situationsCommon pitfallsQuestionsSources
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Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.

Hypoglycaemia

Endocrinology and metabolism · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

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Time-critical presentation

Treat a bedside glucose below 4.0 mmol/L in a hospital patient immediately. If consciousness, airway protection or swallowing is impaired, summon urgent help, use ABCDE, stop oral intake and follow the current JBDS-aligned local parenteral pathway. Do not delay treatment for venous confirmation, and investigate any failure to recover as possible persistent neuroglycopenia or another emergency.

Overview

Recognise and treat low glucose promptly while finding the cause, preventing recurrence and preserving essential background diabetes therapy safely.

Hypoglycaemia is a clinical syndrome of low glucose causing autonomic activation, neuroglycopenia or both. Adrenergic symptoms include sweating, tremor, palpitations, hunger and anxiety; cerebral glucose deprivation causes confusion, behavioural change, visual disturbance, weakness, seizure, coma and injury. Beta-blockade, recurrent episodes, long diabetes duration, sleep and autonomic neuropathy can blunt warning symptoms.

The immediate objective is safe glucose recovery, but the complete task is wider: protect the airway, confirm response, identify iatrogenic or systemic causes, replace longer-acting carbohydrate, adjust treatment and monitor for recurrence. Kidney or liver dysfunction, reduced intake, vomiting, sepsis, weight loss, alcohol, medication error and an unplanned interruption to feed are common contributors.

Hospital algorithms and stocked preparations differ. The treatment quantities below reflect the current JBDS adult hospital guideline, but clinicians must prescribe against the live local hypoglycaemia chart, check the actual glucose concentration and seek senior or diabetes-team support for recurrent, refractory, pregnancy-associated or non-diabetes hypoglycaemia.

Aetiology

01

Insulin or secretagogue treatment

Excess dose, mistimed food, unplanned activity, injection error or reduced clearance can make glucose-lowering treatment exceed physiological need.

02

Reduced substrate or clearance

Poor intake, vomiting, alcohol, liver failure or interrupted enteral feeding limits glucose availability and hepatic release.

03

Critical illness or organ failure

Sepsis, kidney failure and severe systemic disease alter glucose production, use and medicine clearance, often causing recurrent or prolonged episodes.

04

Endogenous hormone disorder

Adrenal insufficiency and inappropriate endogenous insulin secretion are important alternatives when hypoglycaemia occurs without glucose-lowering treatment.

Pathophysiology

  1. 1
    Circulating glucose falls

    Insulin action, impaired production or reduced intake lowers plasma glucose below the level needed for normal tissue supply.

  2. 2
    Autonomic warning activates

    Counter-regulatory sympathetic responses cause sweating, tremor, palpitations, hunger and anxiety, although recurrent episodes or autonomic neuropathy may blunt them.

  3. 3
    Brain glucose delivery fails

    Neuroglycopenia causes behavioural change, confusion, visual disturbance and weakness before progressing to seizure, coma or injury.

Clinical features and red flags

Autonomic warningRed flag

Sweating, tremor, hunger, palpitations, tingling or anxiety may precede cognitive impairment and provide a window for self-treatment when swallowing remains safe.

NeuroglycopeniaRed flag

Irritability, bizarre behaviour, confusion, dysarthria, focal-looking weakness, seizure or reduced consciousness can mimic stroke or intoxication, so glucose belongs in every acute neurological assessment.

Impaired awareness

Absent or late warning symptoms after recurrent hypoglycaemia substantially increase severe-event risk and require avoidance of further lows, treatment review and specialist education.

Nocturnal episode

Disturbed sleep, nightmares, morning headache, unexplained overnight falls or continuous-monitor traces may reveal sleep-associated hypoglycaemia despite no recalled warning symptoms.

Prolonged drug effectRed flag

Renal decline, sulfonylurea use, long-acting insulin, administration error or reduced intake predicts recurrence and often warrants extended observation and specialist medication adjustment.

Investigations

  1. 01
    Immediate capillary blood glucoseFirst step
    Why
    Identify a reversible cause of acute behavioural, neurological or autonomic symptoms at the bedside.
    Interpretation and limitations
    Treat below 4.0 mmol/L without delay; repeat after intervention, and obtain a laboratory sample if the reading conflicts with the clinical picture without postponing rescue treatment.
  2. 02
    Timed glucose rechecks
    Why
    Confirm that rapid carbohydrate or parenteral treatment has produced a durable response.
    Interpretation and limitations
    Recheck 10–15 minutes after oral therapy under JBDS guidance and continue frequent monitoring after recovery; recurrent decline indicates ongoing drug effect, inadequate carbohydrate or unresolved illness.
  3. 03
    Medicine and administration record review
    Why
    Find excess insulin, sulfonylurea exposure, timing errors, duplicated doses or mismatch with nutrition.
    Interpretation and limitations
    Compare prescribed, administered and intended doses with meal, enteral-feed, steroid and renal-function changes; do not assume the electronic prescription reflects what occurred.
  4. 04
    Renal, liver and infection assessment
    Why
    Detect reduced medicine clearance or acute systemic precipitants that prolong hypoglycaemic risk.
    Interpretation and limitations
    Acute kidney injury, hepatic dysfunction, sepsis or malnutrition lowers the threshold for observation, regimen reduction and senior diabetes input.

Differential diagnosis

01

Anxiety or panic

Tremor, sweating and palpitations overlap, but a measured low glucose with symptom resolution after correction supports hypoglycaemia.

02

Stroke or seizure disorder

Focal deficit, confusion or convulsion may be neurological disease; bedside glucose is essential because hypoglycaemia is a rapidly reversible mimic.

03

Postural hypotension

Dizziness and weakness on standing with normal glucose and a blood-pressure fall suggest circulatory rather than glycaemic physiology.

04

Sensor or sampling error

Compression, poor perfusion or device error can produce a low reading without symptoms; confirm when safe without delaying treatment of a clinically convincing episode.

Additional chapter-specific clues

Alternative or additional emergencyRed flag

Persistent coma, focal deficit, fever, trauma, toxic exposure or failure to improve after glucose correction means another diagnosis must be assessed in parallel.

Management

01ConsciousTreat when swallowing is safeFirst stepGlucose is below 4.0 mmol/L and the adult is alert, cooperative and able to swallow safely.+
  1. 1Give 15–20 g rapid-acting carbohydrate using a stocked option compatible with swallowing ability and any fluid or renal restriction, following the local JBDS-aligned chart.
  2. 2EscalationRecheck capillary glucose after 10–15 minutes; if it remains below 4.0 mmol/L, repeat the rapid treatment and reassess, using the escalation route if three cycles fail.
  3. 3After recovery, give a longer-acting carbohydrate snack or planned meal, resume appropriate diabetes treatment safely and investigate why supply and insulin action became mismatched.
02Unsafe swallowProtect airway and use parenteral rescueThe patient is unconscious, fitting, severely confused, uncooperative or otherwise unable to take carbohydrate safely by mouth.+

Complications

01

Neurological injury

Prolonged cerebral glucose deprivation can cause seizure, coma, focal deficits and potentially persistent cognitive or neurological impairment.

02

Trauma and driving risk

Impaired judgement, vision and consciousness can cause falls, road collisions or workplace injury before the person can self-treat.

03

Cardiac arrhythmia

Adrenergic activation and repolarisation changes can provoke rhythm disturbance, particularly during nocturnal episodes or in underlying cardiac disease.

04

Impaired awareness and recurrence

Repeated episodes blunt autonomic warning, creating a cycle of later recognition, severe events and fear-driven avoidance of effective diabetes treatment.

Monitoring and follow-up

  • Repeat bedside glucose at the interval specified by the treatment pathway until above 4.0 mmol/L with clinical recovery, then continue checks long enough to demonstrate stability.
  • Observe airway, respiratory effort, circulation, temperature and neurological state throughout severe episodes; a numerical correction without neurological improvement is not successful resuscitation.
  • After sulfonylurea or long-acting insulin exposure, anticipate recurrent low glucose for at least the period defined by toxicology, diabetes and local guidance, particularly when renal clearance is reduced.
  • Audit the relationship between insulin administration, meals, enteral feed, steroid dose and procedures, including whether omitted or delayed nutrition caused the event.
  • Record whether another person’s assistance was required, whether awareness was impaired and whether the event affects driving, work, discharge or access to glucose-monitoring technology.
  • Arrange early review after a severe or recurrent event to confirm the amended regimen, education, rescue supplies and restoration of warning symptoms where possible.

Special situations

Treat the patient and reading

Low bedside glucose can explain dramatic neurological behaviour, but persistent focal signs after correction still require urgent stroke, seizure or structural assessment.

Basal insulin still matters

A person with type 1 diabetes requires basal insulin even after hypoglycaemia; reduce and redesign safely rather than creating insulin deficiency and ketoacidosis.

Recovery needs slower carbohydrate

Rapid sugar corrects the immediate nadir, whereas a meal or longer-acting carbohydrate helps bridge ongoing insulin action after consciousness and swallowing recover.

Renal change predicts recurrence

An unchanged home dose can become excessive during acute kidney injury, so medicine reconciliation must use current organ function rather than historic tolerance.

Severe has a functional meaning

A severe episode is defined by needing external assistance, not solely by a particular meter value; document that feature for risk and driving review.

Technology does not abolish risk

Continuous monitoring alerts can reduce exposure but lag, compression artefact, alarm fatigue or inability to respond means clinical symptoms and confirmatory checks still matter.

Common pitfalls

  1. 01

    Giving oral glucose to a drowsy person whose swallowing is unsafe, converting a metabolic emergency into an aspiration emergency.

  2. 02

    Celebrating the first reading above 4.0 mmol/L without longer-acting carbohydrate, medication review or observation for recurrent drug effect.

  3. 03

    Omitting every form of insulin after an episode in type 1 diabetes and thereby creating preventable ketogenesis and diabetic ketoacidosis.

  4. 04

    Assuming glucagon will work reliably in prolonged fasting, alcohol-related depletion, severe liver disease or sulfonylurea-associated hypoglycaemia.

  5. 05

    Failing to check whether an enteral feed, meal, glucose-containing substrate fluid or steroid dose was interrupted after insulin had already been administered.

  6. 06

    Discharging after a severe event without documenting assistance, awareness, regimen changes, rescue education and applicable DVLA advice.

Practice

Two practice questions

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Question 1 of 2
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Endocrinology and metabolismOriginal SBA

Conscious inpatient treatment

A conscious cooperative inpatient taking insulin feels sweaty and shaky. Capillary glucose is 3.1 mmol/L and swallowing is safe. What is the best immediate action?

Choose one answer, then submit
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Sources and review status4 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

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.

  • JBDS 01 hospital hypoglycaemia guidelineCurrent official adult inpatient definitions, oral and parenteral rescue, reassessment and recurrence guidance.
  • NICE NG17 type 1 diabetes recommendationsHypoglycaemia education, awareness, technology and insulin-management recommendations.
  • NICE NG28 type 2 diabetes recommendationsPerson-centred glycaemic targets and treatment review relevant to prevention.
  • DVLA diabetes fitness to drive guidanceCurrent statutory medical standards and definitions relevant after severe or recurrent hypoglycaemia.

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateComplete draftClinical stateAwaiting reviewJurisdictionUnited Kingdom

Key points

  • Think ‘four is the floor’: a capillary reading below 4.0 mmol/L requires action in an adult inpatient even when symptoms are subtle or absent.
  • Choose treatment by consciousness and swallow safety, not by the number alone; oral carbohydrate is unsafe in a drowsy, fitting or uncooperative patient.
  • For a conscious cooperative adult, JBDS uses 15–20 g rapid-acting carbohydrate followed by a glucose recheck after 10–15 minutes and repeat treatment if still low.
  • Once glucose is above 4.0 mmol/L and the person has recovered, give longer-acting carbohydrate or the planned meal and review the medicine that created risk.
  • Sulfonylurea and long-acting insulin hypoglycaemia may recur for 24–36 hours, especially with renal impairment; a single normal result is not a discharge test.
  • Glucagon may be less effective after repeated episodes, prolonged fasting, alcohol excess, liver disease or sulfonylurea exposure, so arrange reliable glucose delivery and monitoring.
  • During an active intravenous insulin infusion, pause it while treating the low glucose and restart safely once corrected according to the indication and local chart.
  • Document precipitant, severity, awareness, assistance required and prevention changes; provide driving advice when the event meets current DVLA relevance.
  • 05
    Critical sample in unexplained spontaneous hypoglycaemia
    Why
    Support investigation of endogenous insulin, endocrine, organ-failure or drug-related causes outside known diabetes treatment.
    Interpretation and limitations
    When clinically safe and before carbohydrate if this causes no treatment delay, obtain locally specified paired laboratory tests with endocrine advice; never recreate or prolong a low glucose for sampling.
    • 1
    Call for urgent assistance, use ABCDE, place the patient in a safe position, secure intravenous access if possible and do not put food or fluid into the mouth.
  • 2Use the current local parenteral algorithm: JBDS options include intravenous 20% or 10% glucose, or intramuscular glucagon when intravenous access is not available and its limitations are understood.
  • 3EscalationRecheck promptly, repeat or escalate treatment according to the chart, and assess another neurological or toxic cause if consciousness does not recover despite correction.
    • 03PreventComplete post-event careThe glucose has risen above 4.0 mmol/L and immediate clinical recovery is established.+
    1. 1Provide longer-acting carbohydrate when appropriate, continue scheduled monitoring and extend observation when a sulfonylurea, long-acting insulin, renal impairment or uncertain ingestion creates delayed risk.
    2. 2Review insulin and glucose-lowering medicines with intake, weight, renal function, steroids, activity and intercurrent illness; preserve necessary basal insulin in type 1 diabetes through an adjusted safe plan.
    3. 3Explain recurrence prevention, hypo treatment supplies, awareness, when to seek help and current DVLA responsibilities, and send a clear regimen change to the next care team.
    04InfusionCorrect a low during intravenous insulinHypoglycaemia occurs while a variable- or fixed-rate intravenous insulin infusion is running.+
    1. 1Stop the active insulin infusion temporarily, treat the hypoglycaemia by consciousness and swallow status, and check that substrate fluid has not been interrupted or prescribed incorrectly.
    2. 2Reassess the indication, recent rate, potassium, nutrition and concurrent subcutaneous basal insulin; DKA, HHS and general inpatient infusions require different restart logic.
    3. 3Once glucose is safely corrected, restart or replace insulin using the dedicated local protocol with senior or diabetes-team review rather than leaving essential insulin omitted.
    Key medicines and prescribing safety3 treatments · regimens, roles and cautions+
    First-line rescue when airway protection and swallowing are intact and rapid intestinal absorption is reliable.

    Rapid-acting oral carbohydrate

    Give 15–20 g of rapid-acting carbohydrate to a conscious cooperative adult, then recheck glucose after 10–15 minutes and repeat if it remains below 4.0 mmol/L, using the current local JBDS-aligned options.

    Do not give orally with reduced consciousness, seizure, unsafe swallow or aspiration risk. Choose a preparation compatible with fluid restriction and swallowing difficulty; chocolate and other high-fat foods act too slowly for initial rescue.

    Provides dependable glucose delivery for severe neuroglycopenia when oral treatment is unsafe or ineffective.

    Intravenous glucose for severe hypoglycaemia

    JBDS lists 100 mL of 20% glucose over 15 minutes or 200 mL of 10% glucose over 15 minutes for an adult when intravenous treatment is required; prescribe the stocked concentration on the live local chart.

    Confirm concentration and line patency, monitor for extravasation and fluid considerations, and recheck glucose promptly. Avoid confusing different strengths or giving an unprescribed rapid bolus; follow resuscitation and local medicines policy.

    Mobilises hepatic glucose as a temporary rescue option where immediate intravenous glucose cannot be delivered.

    Glucagon

    JBDS uses 1 mg intramuscularly when intravenous access is not available in severe insulin-associated hypoglycaemia; position safely, seek access and follow the current product and local emergency instructions.

    Response may be poor after prolonged fasting, alcohol excess, chronic liver disease, repeated hypoglycaemia or sulfonylurea exposure. Nausea and vomiting create aspiration risk, and recovery still requires carbohydrate, monitoring and cause correction.