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Glucose Abnormalities: MCCQE1 Preparation Guide

Understanding glucose abnormalities—ranging from life-threatening hypoglycemia to hyperglycemic emergencies like DKA and HHS—is a cornerstone of the Medical Council of Canada Qualifying Examination Part I (MCCQE1). As a future Canadian physician, you must demonstrate competence in the Medical Expert role by diagnosing, managing, and preventing these conditions according to Diabetes Canada Clinical Practice Guidelines.

This guide is optimized for MCCQE1 preparation, focusing on high-yield concepts, Canadian diagnostic criteria (mmol/L), and management protocols.

Hypoglycemia

Hypoglycemia is a medical emergency that requires immediate recognition and treatment. In the context of the MCCQE1, always prioritize patient safety.

Definition and Diagnosis

Hypoglycemia is clinically defined by Whipple’s Triad:

  1. Symptoms consistent with hypoglycemia (autonomic or neuroglycopenic).
  2. Low plasma glucose concentration (typically <4.0 mmol/L for patients treated with insulin or secretagogues).
  3. Resolution of symptoms after plasma glucose concentration is raised.

Clinical Presentation

Symptoms are categorized into neurogenic (autonomic) and neuroglycopenic.

Neurogenic (Autonomic)

Triggered by catecholamine release.

  • Trembling/Shaking
  • Palpitations
  • Sweating/Diaphoresis
  • Anxiety
  • Hunger

Neuroglycopenic

Result of brain glucose deprivation.

  • Confusion/Difficulty concentrating
  • Weakness/Drowsiness
  • Vision changes
  • Difficulty speaking
  • Seizures or Coma

Management of Hypoglycemia

The management depends on the patient’s level of consciousness and ability to swallow.

Step 1: Conscious Patient (The “Rule of 15”)

If the patient is conscious and able to swallow:

  1. Administer 15 g of fast-acting carbohydrate (e.g., 4 glucose tablets, 175 mL of juice/regular pop, 1 tbsp honey).
  2. Wait 15 minutes.
  3. Retest blood glucose.
  4. If still <4.0 mmol/L, repeat treatment.
  5. Once treated, provide a snack (protein + carb) or meal if the next meal is >1 hour away.

Step 2: Unconscious Patient (No IV Access)

If the patient cannot swallow or is unconscious in a non-hospital setting:

  1. Administer Glucagon 1 mg SC or IM (or 3 mg intranasal).
  2. Call emergency services (911).
  3. Roll patient to the side (recovery position) as glucagon may cause vomiting.

Step 3: Unconscious Patient (IV Access Available)

In a hospital setting (ER/Ward):

  1. Administer Dextrose 50% (D50W) IV push (usually 25g, which is 50 mL).
  2. Start IV maintenance fluid (D5W or D10W) to prevent rebound hypoglycemia.
  3. Monitor capillary blood glucose (CBG) q15min until stable.
⚠️

MCCQE1 Tip: Sulfonylurea-induced hypoglycemia can be prolonged and recurrent. These patients often require observation for at least 24 hours and may need Octreotide if hypoglycemia is refractory to dextrose.

Hyperglycemia and Diabetes Mellitus

Diabetes Mellitus (DM) is a metabolic disorder characterized by hyperglycemia. For the MCCQE1, you must master the diagnostic criteria set by Diabetes Canada.

Classification

Autoimmune destruction of pancreatic beta-cells leading to absolute insulin deficiency. Typically presents in youth with polyuria, polydipsia, polyphagia, and weight loss. Prone to DKA.

Diagnostic Criteria (Non-Pregnant Adults)

TestDiabetes ThresholdPrediabetes Threshold
Fasting Plasma Glucose (FPG)≥ 7.0 mmol/L6.1 – 6.9 mmol/L (IFG)
A1C≥ 6.5%6.0 – 6.4%
2h Plasma Glucose (75g OGTT)≥ 11.1 mmol/L7.8 – 11.0 mmol/L (IGT)
Random Plasma Glucose≥ 11.1 mmol/L (+ symptoms)-

Abbreviations: IFG = Impaired Fasting Glucose; IGT = Impaired Glucose Tolerance.

Note: In the absence of symptomatic hyperglycemia, a confirmatory test is required on a subsequent day (unless two different tests are positive simultaneously).

Acute Hyperglycemic Emergencies

Distinguishing between Diabetic Ketoacidosis (DKA) and Hyperosmolar Hyperglycemic State (HHS) is a high-yield MCCQE1 objective.

Comparison: DKA vs. HHS

FeatureDiabetic Ketoacidosis (DKA)Hyperosmolar Hyperglycemic State (HHS)
Primary PatientType 1 DM (usually)Type 2 DM (usually elderly)
OnsetRapid (<24 hours)Insidious (days to weeks)
Glucose>14.0 mmol/L (often higher)>34.0 mmol/L (often very high)
pH<7.3 (Acidotic)>7.3 (Normal)
Bicarbonate<15 mmol/L>15 mmol/L
KetonesPositive (Serum/Urine)Negative or Trace
OsmolalityVariable>320 mOsm/kg
Mental StatusAlert to drowsyStupor/Coma (correlates with osmolality)

Management Protocol

The management principles are similar: Fluids, Potassium, Insulin (KPI mnemonic).

Management Priorities

  1. Volume Resuscitation: This is the FIRST and most critical step.
  2. Electrolyte Correction: specifically Potassium (K+).
  3. Hyperglycemia Correction: Insulin infusion.
  4. Precipitating Cause: Treat infection, MI, missed insulin, etc.

Step 1: Fluid Resuscitation

Start IV Normal Saline (0.9% NaCl) immediately.

  • Shock: 1-2 L bolus.
  • Hypovolemic but stable: 500 mL/hr for 4 hours.
  • Switch to 0.45% NaCl if sodium is high/normal and patient is hemodynamically stable.
  • Add Dextrose (D5W) to IV fluids when plasma glucose reaches 14.0 mmol/L (DKA) or 16.7 mmol/L (HHS) to prevent hypoglycemia while continuing insulin to clear ketones.

Step 2: Potassium Management

Do NOT start insulin until K+ is known. Insulin shifts K+ into cells, causing fatal arrhythmias.

  • K+ < 3.3 mmol/L: Hold insulin. Give IV KCl (10-40 mmol/hr).
  • K+ 3.3 – 5.0 mmol/L: Give IV KCl (20-40 mmol/L of IV fluid) with insulin.
  • K+ > 5.0 mmol/L: Start insulin alone; monitor K+ q2h.

Step 3: Insulin Therapy

Start IV Regular Insulin infusion (0.1 units/kg/hr).

  • Avoid bolus in children (risk of cerebral edema).
  • Goal: Lower glucose by 3–4 mmol/L per hour.
  • Continue IV insulin until anion gap closes (DKA) or mental status clears (HHS), then overlap with SC insulin by 1-2 hours.

Canadian Guidelines

For MCCQE1 preparation, familiarity with the Diabetes Canada 2018 Clinical Practice Guidelines (and subsequent updates) is essential.

Screening (CANRISK)

  • Screen every 3 years in individuals ≥40 years of age.
  • Screen earlier or more frequently in high-risk individuals (e.g., first-degree relative with DM, high-risk populations including Indigenous, South Asian, African, Hispanic descent).
  • Use the CANRISK questionnaire score to stratify risk.

Glycemic Targets

  • A1C < 7.0%: Most adults with Type 1 or Type 2 DM.
  • A1C < 6.5%: Consider for adults with T2DM to reduce risk of nephropathy/retinopathy if achieved safely (no hypoglycemia).
  • A1C 7.1 – 8.5%: Functionally dependent, limited life expectancy, or history of severe hypoglycemia (frail elderly).

Driving Guidelines (CMA)

  • Physicians have a duty to report patients who are unfit to drive.
  • Patients with hypoglycemia unawareness or severe recurrent hypoglycemia usually face license suspension until stable.

Key Points to Remember for MCCQE1

  • Glucose Toxicity: In HHS, the severe dehydration is due to osmotic diuresis caused by massive hyperglycemia.
  • Anion Gap: Always calculate the anion gap in hyperglycemic patients: AG=Na+−(Cl−+HCO3−)AG = Na^+ - (Cl^- + HCO_3^-). Normal is approx 12. In DKA, AG is elevated (>12).
  • Cerebral Edema: The most feared complication of DKA treatment in children. Avoid rapid shifts in osmolality. Signs: Headache, bradycardia, decreasing GCS. Rx: Mannitol or Hypertonic Saline.
  • Beta-Blockers: Can mask the adrenergic/autonomic symptoms of hypoglycemia (tremor, palpitations) but not the sweating.
  • Sick Day Management: Patients should never stop insulin completely when sick, even if not eating, as stress hormones increase glucose. They may need frequent monitoring and supplemental insulin.

Sample Question

Case Presentation

A 72-year-old man presents to the emergency department brought by his daughter. She reports that he has been increasingly confused and lethargic over the past 3 days. He has a history of Type 2 Diabetes Mellitus managed with Metformin, but he ran out of medication a week ago. On examination, he is stuporous but responds to pain. Vital signs are: BP 95/60 mmHg, HR 118 bpm, RR 20/min, Temp 37.1°C. Mucous membranes are extremely dry, and skin turgor is poor.

Laboratory investigations reveal:

  • Glucose: 42.0 mmol/L
  • Sodium: 148 mmol/L
  • Potassium: 3.9 mmol/L
  • Bicarbonate: 20 mmol/L
  • pH: 7.36
  • Serum Ketones: Negative

Which one of the following is the most appropriate initial step in the management of this patient?

  • A. Administer IV Regular Insulin bolus 0.1 units/kg
  • B. Administer IV Sodium Bicarbonate
  • C. Administer IV 0.9% Normal Saline 1000 mL bolus
  • D. Administer IV 3% Hypertonic Saline
  • E. Administer IV Potassium Chloride 40 mmol

Explanation

The correct answer is:

  • C. Administer IV 0.9% Normal Saline 1000 mL bolus

Detailed Explanation:

This patient presents with Hyperosmolar Hyperglycemic State (HHS). The diagnosis is supported by the patient’s age (elderly), Type 2 DM history, severe hyperglycemia (>34 mmol/L), profound dehydration (dry mucous membranes, hypotension, tachycardia), altered mental status, and lack of significant acidosis or ketosis (pH > 7.3, Bicarb > 15, negative ketones).

  1. Fluid Resuscitation (Option C): This is the most critical initial step. Patients with HHS are severely dehydrated (often 8-10L deficit). Immediate expansion of intravascular volume is required to restore perfusion and reduce counter-regulatory hormones. Isotonic saline (0.9% NaCl) is the fluid of choice for the initial bolus.
  2. Insulin (Option A): While insulin is required, it should never be the first step before fluids. Starting insulin before fluids can drive glucose and water into cells, worsening intravascular collapse and hypotension. Furthermore, insulin should be delayed until potassium is confirmed to be >3.3 mmol/L (though in this case, K is 3.9, fluid remains the priority).
  3. Sodium Bicarbonate (Option B): This is contraindicated. The patient is not significantly acidotic (pH 7.36). Bicarbonate is generally only considered in severe acidosis (pH < 6.9 or 7.0) in DKA, which this patient does not have.
  4. Hypertonic Saline (Option D): This is used for severe symptomatic hyponatremia or cerebral edema. It would worsen this patient’s hyperosmolar state.
  5. Potassium (Option E): While this patient will need potassium replacement (as insulin will drive K+ into cells), the immediate life-threatening issue is hypovolemic shock. Potassium is added to the maintenance fluids once urine output is established and insulin is started, but the initial step is volume expansion.

References

  1. Diabetes Canada Clinical Practice Guidelines Expert Committee. Diabetes Canada 2018 Clinical Practice Guidelines for the Prevention and Management of Diabetes in Canada. Can J Diabetes. 2018;42(Suppl 1):S1-S325. Available at guidelines.diabetes.ca 
  2. Medical Council of Canada. Objectives for the Qualifying Examination. mcc.ca 
  3. Kasper, D. L., et al. Harrison’s Principles of Internal Medicine. 20th Edition. McGraw-Hill Education.
  4. Toronto Notes Editors. Toronto Notes 2024: Comprehensive Medical Reference and Review for the Medical Council of Canada Qualifying Exam Part I. Toronto Notes.
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