Hypoglycaemia

• Whipple's triad is the gold standard definition ^[1][2][3]:
  1. Symptoms of hypoglycaemia (adrenergic and/or neuroglycopenic)
  2. Documented low plasma glucose concentration at the time symptoms are present
  3. Relief of symptoms upon correction of the low glucose (by oral glucose, IV dextrose, or IM glucagon)

Why all three criteria? Because many non-specific symptoms (anxiety, tremor, sweating) overlap with other conditions. A low glucose reading alone is also insufficient — some healthy individuals (especially lean young women) may have transiently low glucose without symptoms. Therefore, you must demonstrate the causal link: symptoms + low glucose + resolution. ^[1][2]

• Defined as all episodes of an abnormally low plasma glucose concentration (with or without symptoms) that expose the individual to harm ^[2]
• Threshold: plasma glucose ≤ 3.9 mmol/L by self-monitored blood glucose (SMBG) or continuous glucose monitoring (CGM) ^[2][3]
• A higher threshold is deliberately used because:
  • 3.9 mmol/L is the lower limit of the physiological fasting glucose range ^[2]
  • 3.9 mmol/L is the normal glycaemic threshold for counter-regulatory hormone secretion ^[2]
  • 3.9 mmol/L is the highest antecedent low glucose level reported to reduce the sympathoadrenal response to subsequent hypoglycaemia (i.e., if you allow repeated drops to 3.9, the body "resets" and won't warn you next time until even lower — this is hypoglycaemia unawareness) ^[2]
  • Early detection is paramount in insulin-treated patients because they are at high probability of recurrent episodes

Three levels of hypoglycaemia — anything below 4.0 mmol/L is the threshold ^[3][4]:

• Hypoglycaemia is overwhelmingly most common as a side effect of diabetes treatment — it is the most frequent acute complication of insulin therapy
• In Type 1 DM: virtually all patients experience hypoglycaemia at some point; average 1–2 symptomatic episodes per week, with severe episodes ~0.2–3.2 per patient-year ^[2]
• In Type 2 DM: less common early on (when treated with metformin/lifestyle), but becomes increasingly common as disease progresses and patients are started on insulin or sulphonylureas
• Spontaneous hypoglycaemia (in non-diabetic individuals) is uncommon and should always prompt investigation for a serious underlying cause (insulinoma, adrenal insufficiency, liver failure, etc.) ^[1]

In diabetic patients (the vast majority of cases):

In non-diabetic patients ("spontaneous hypoglycaemia"):

• Have to ask for weight — patients with recurrent hypoglycaemia develop "defensive eating" and tend to gain weight from snacking to avoid symptoms ^[1]
• Risk factors relate to the underlying aetiology (see Aetiology section below)

1. Liver — the glucose "bank"

   • Stores glucose as glycogen (glycogenesis) after meals
   • Releases glucose via glycogenolysis (breakdown of glycogen) during fasting
   • Produces new glucose via gluconeogenesis (from lactate, glycerol, amino acids like alanine and glutamine) during prolonged fasting
   • Responsible for ~80% of endogenous glucose production

2. Kidneys — the overlooked contributor

   • Contribute ~20% of gluconeogenesis during fasting (primarily from glutamine in the renal cortex)
   • Also reabsorb filtered glucose (via SGLT2 in proximal tubule) — relevant to SGLT2 inhibitor therapy

3. Pancreas — the master regulator

   • Beta cells (islets of Langerhans): secrete insulin in response to rising glucose → promotes glucose uptake and storage
   • Alpha cells: secrete glucagon in response to falling glucose → stimulates hepatic glycogenolysis and gluconeogenesis
   • Delta cells: secrete somatostatin → modulates insulin and glucagon release

4. Skeletal muscle — the major glucose consumer

   • Takes up ~70–80% of glucose after an oral glucose load (insulin-dependent, via GLUT4)
   • During exercise, glucose uptake can increase dramatically via AMPK-mediated GLUT4 translocation (insulin-independent)

5. Brain — the obligate glucose consumer

   • Uses ~120g glucose/day (~60% of whole-body glucose utilisation at rest)
   • Cannot store significant glycogen and cannot use fatty acids as fuel under normal conditions
   • This is why neuroglycopenic symptoms dominate when glucose falls — the brain is the first organ to suffer

6. Adipose tissue

   • Lipolysis (triglyceride → glycerol + free fatty acids) is suppressed by insulin
   • Glycerol serves as a gluconeogenic substrate
   • Free fatty acids serve as alternative fuel for muscle, heart, and liver (sparing glucose for the brain)

When blood glucose falls, the body mounts a hierarchical counter-regulatory response. Understanding this hierarchy explains the symptom progression of hypoglycaemia:

• Diabetic hypoglycaemia (iatrogenic — by far the most common)
• Non-diabetic (spontaneous) hypoglycaemia (warrants full investigation)

• Fasting hypoglycaemia — occurs during fasting or > 5h after last meal
• Postprandial (reactive) hypoglycaemia — occurs 2–4h after a meal

• Insulin-mediated (↑insulin): endogenous (insulinoma, SU) or exogenous (insulin injection)
• Non-insulin-mediated (↓insulin): decreased glucose production or non-insulin-mediated increased utilisation

• Level 1 ( < 3.9 mmol/L), Level 2 ( < 3.0 mmol/L), Level 3 (severe — needs external help) ^[3]

These symptoms activate the same sympathoadrenal axis, so any condition that drives catecholamine release or mimics it will look similar:

This is where hypoglycaemia becomes a dangerous mimic — it can look like stroke, epilepsy, intoxication, or psychosis.

When a patient presents with transient LOC (TLOC), hypoglycaemia sits alongside several major categories ^[16][17]:

Key point: LOC only occurs in syncope and seizure categories among the "faints and fits" differentials — it suggests generalised brain dysfunction ^[16][17]. Hypoglycaemia can cause LOC via either mechanism (substrate deprivation → direct neuronal failure, or provoking a seizure).

This is usually straightforward — the cause is almost always iatrogenic:

Four general causes to remember: ^[3]

1. Too much sulphonylurea or insulin
2. Too little carbohydrate
3. Too much exercise
4. Exclude renal impairment — many T2DM patients

This is where the diagnostic challenge lies. A systematic approach using the insulin / C-peptide framework at the time of hypoglycaemia is essential ^[1][5][9]:

The approach in neonates and children differs because of unique aetiologies ^[13]:

ALWAYS take urine ketone and critical samples during a hypoglycaemic episode in a child — this is a one-off opportunity to determine the cause ^[13].

Clues to specific paediatric diagnoses ^[13]:

• Micropenis → hypopituitarism (severe GH deficiency)
• Midline defects (cleft lip/palate) → hypothalamic-pituitary abnormality
• Big tongue, body asymmetry → Beckwith-Wiedemann syndrome (BWS)
• History of fundoplication → dumping syndrome
• Unexplained hypoglycaemia + seizures + developmental regression → inborn error of metabolism ^[18]

• Low H'stix should be confirmed with venous blood random glucose ^[5] — finger-prick is a screening tool, not diagnostic
• Document symptoms at time of low glucose
• Demonstrate relief with glucose administration

• Yes → Review medications (insulin, SU), dietary intake, exercise, renal function, hepatic function, alcohol
• No → Proceed to "spontaneous hypoglycaemia" workup

• Insulinoma → fasting hypoglycaemia (eating wards it off; symptoms recur 4–5h after eating stops) ^[1]
• Post-gastrectomy → postprandial hypoglycaemia (3–4h after a meal, exaggerated insulin response) ^[1]

• Plasma glucose (venous), insulin, C-peptide, ± BHBA, ± cortisol, ± GH, ± anti-insulin antibody, ± urine sulphonylurea screen ^[5][9]
• If cannot catch a spontaneous episode → prolonged fasting test (72-hour supervised fast) ^[5]

• Short Synacthen test + ACTH → Addison's disease ^[1][5]
• Glucagon stimulation test → GH deficiency ^[1][5][12]
• Imaging (CT abdomen, MRI pancreas, endoscopic USS) → insulinoma localisation
• IGF-2, IGFBP-3 → NICTH
• Prolonged OGTT → reactive hypoglycaemia (limited use) ^[9]

There is no single "diagnostic criterion" for hypoglycaemia in the way there is for DM. Instead, the diagnosis rests on Whipple's triad — a clinico-biochemical construct originally described in the context of insulinoma, but now applied universally ^[1][2][5]:

Whipple's triad was originally described as the clinical presentation of pancreatic insulinoma and consists of: (1) fasting hypoglycaemia ( < 50 mg/dL or < 2.7 mmol/L), (2) symptoms of hypoglycaemia, (3) immediate relief of symptoms after the administration of intravenous glucose. ^[1]

For patients with DM, the diagnostic approach is simpler because the context (diabetes treatment) already provides the explanation. The Endocrine Society / ADA definition:

• Blood glucose ≤ 3.9 mmol/L (with or without symptoms) constitutes hypoglycaemia ^[2][3]
• Severity grading as previously described (Level 1 / 2 / 3)

Why is the threshold higher than the Whipple's triad value? Because diabetic patients on insulin or secretagogues are at high probability of recurrent episodes, and detecting them early (before neuroglycopenia) allows pre-emptive intervention. Waiting for "classic" Whipple's triad in a diabetic patient is dangerous — by then, the patient may already have impaired judgement ^[2].

A critical practical point:

"Spot glucose" at bedside is the first step — but always send a venous plasma glucose simultaneously to confirm ^[1][5]. POCT glucose is not acceptable for definitive diagnosis, just as it is not acceptable for OGTT ^[12].

The single most important step in the workup of unexplained hypoglycaemia is obtaining a critical sample at the time of documented hypoglycaemia ^[1][5][9]. This is often a one-off opportunity — the biochemical relationships between insulin, C-peptide, and glucose are only interpretable when measured simultaneously during hypoglycaemia.

These are not diagnostic for the cause of hypoglycaemia per se, but are essential for the full clinical picture ^[9]:

Imaging is performed AFTER biochemical confirmation — endocrine is unique in that you need biochemistry before imaging ^[22].

In children, the pattern of FFA and ketones is key ^[13]:

Rule of 15: Give 15g glucose → wait 15 minutes → recheck glucose → if still < 3.9, repeat. Once > 3.9, give a carbohydrate meal.

Option 1: IV Dextrose (Preferred if IV access available)

Why not just give a large bolus and stop? Because the underlying cause (insulin, SU) may still be active. A single bolus raises glucose transiently, but without ongoing infusion the glucose will crash again. Sulphonylurea-induced hypoglycaemia in particular may require prolonged IV dextrose infusion for days ^[5][9].

Option 2: IM Glucagon (When IV Access Cannot Be Obtained)

The key teaching point: too aggressive management of diabetes is associated with greater mortality due to greater chance of developing hypoglycemia ^[3].

Medication-Specific Adjustments

The management is entirely directed at the specific aetiology:

Must exclude MEN1 (Multiple Endocrine Neoplasia type 1) — insulinoma is one of the pancreatic NETs associated with MEN1 ^[9]:

• Prolonged fasting test (72h supervised fast) ^[5][9]
• Localisation studies (CT, MRI, EUS, ± SACST) ^[9]

• In general, insulin therapy for frail older adults should be simple and once or twice daily dose of intermediate-acting insulin is sufficient ^[25]
• Consider long-acting basal insulin analogue (glargine, detemir) if recurrent nocturnal or pre-meal hypoglycaemia ^[25]
• May add pre-prandial rapid-acting insulin analogue (lispro, aspart) if profound post-prandial hyperglycaemia ^[25]
• Short-acting sulphonylurea to minimize the risk of hypoglycaemia ^[25]
• SMBG should not be routinely advised to monitor post-prandial hyperglycaemia but sometimes indicated to detect fasting or pre-meal hypoglycaemia ^[25]

A unique challenge: not just β-cells (insulin) but also α-cells (glucagon) are destroyed ^[28]:

• All DM drugs focus on pushing glucose down
• But now the patient also lacks glucagon → no counter-regulatory "safety net" → high risk of severe, refractory hypoglycaemia
• Insulin dosing must be very cautious; frequent small meals essential; close monitoring mandatory

• Always give IV thiamine BEFORE or WITH IV dextrose — glucose metabolism requires thiamine (cofactor for pyruvate dehydrogenase and α-ketoglutarate dehydrogenase); giving dextrose to a thiamine-depleted patient can precipitate Wernicke's encephalopathy
• Correct dehydration and electrolytes
• Address underlying alcohol use disorder

The brain is the organ most vulnerable to hypoglycaemia because it:

• Consumes ~120g glucose/day (~60% of whole-body glucose at rest)
• Has virtually no glycogen stores (only ~2g, lasting minutes)
• Cannot use free fatty acids as fuel under normal conditions
• Relies almost entirely on circulating glucose delivered via GLUT1 (endothelial) and GLUT3 (neuronal) transporters

Hypoglycaemia triggers a massive sympathoadrenal response — essentially a catecholamine storm — which places the cardiovascular system under acute stress:

This is arguably the most clinically important chronic complication because it creates a self-perpetuating vicious cycle:

Note that the threshold for awareness of hypoGly varies between individuals and circumstances → especially note gradual ↓awareness in recurrent hypoglycaemia (e.g., chronic DM) ^[5]

Why does this matter? A T1DM patient with long-standing disease has lost both their first defence (glucagon) and their second defence (adrenaline). They are essentially "defenceless" against hypoglycaemia — this is why T1DM patients are at much higher risk of severe hypoglycaemia than T2DM. Hypoglycaemia is more common in T1DM because of (1) exogenous insulin (higher risk) and (2) absolute insulin deficiency leading to loss of α-cell regulation by β-cells ^[5].

The DCCT (Diabetes Control & Complications Trial) in T1DM demonstrated that intensive therapy reduces microvascular complications: ^[4]

• Primary prevention: retinopathy ↓53%, microalbuminuria ↓10%
• Secondary prevention: retinopathy progression ↓70%, microalbuminuria ↓70%
• Faster motor and sensory nerve conduction velocities
• Lower total cholesterol levels

BUT:

• Intensive therapy associated with 2–4 fold ↑ in severe hypoglycaemia ^[4]

This is the fundamental tension in diabetes management: tighter control prevents chronic microvascular complications but increases the risk of acute hypoglycaemia.

Neonatal hypoglycaemia poses significant risk for developmental sequelae if severe, undetected, and untreated ^[29]:

• The neonatal brain is particularly vulnerable because it is growing rapidly and has limited ability to use ketones as alternative fuel in the first days of life
• Prompt treatment required to reduce risk of CNS complications ^[29]
• Complications include: seizures, intellectual disability, cerebral palsy, cortical visual impairment
• In BWS: management includes frequent feedings including carbohydrate-rich feeds; IV glucose for refractory cases; medications for persistent hypoglycaemia (glucagon, octreotide, diazoxide, nifedipine) ^[29]

• Maternal hypoglycaemia can impair foetal glucose supply (glucose crosses the placenta by facilitated diffusion via GLUT1)
• Tight glycaemic control in gestational DM / pre-existing DM during pregnancy increases hypoglycaemia risk
• Severe maternal hypoglycaemia → risk of maternal falls, MVA, loss of consciousness → foetal harm

• Falls → hip fractures (high mortality in elderly)
• Confusion → misdiagnosed as dementia or delirium → inappropriate institutionalisation
• Arrhythmia → sudden death (already compromised cardiac reserve)
• Cognitive decline → accelerated progression to dementia