12.1 Diabetes Mellitus, Hypoglycemia & Metabolic Emergencies
Key Takeaways
- Diabetes mellitus is diagnosed by fasting plasma glucose ≥126 mg/dL, 2-hour 75g OGTT ≥200 mg/dL, HbA1c ≥6.5%, or random plasma glucose ≥200 mg/dL with classic hyperglycemic symptoms.
- First-line T2DM pharmacotherapy is metformin (contraindicated if eGFR <30 mL/min/1.73m²); SGLT2 inhibitors and GLP-1 receptor agonists provide proven organ protection in CKD, heart failure, or ASCVD.
- Diabetic Ketoacidosis (DKA) features blood glucose >250 mg/dL, arterial pH <7.30, serum bicarbonate <18 mEq/L, and anion gap >12 mEq/L, whereas HHS presents with blood glucose >600 mg/dL without marked ketoacidosis.
- In DKA and HHS management, insulin must be withheld if serum potassium is <3.3 mEq/L until potassium is repleted, and IV 5% dextrose is added when blood glucose drops to ≤200 mg/dL (DKA) or ≤300 mg/dL (HHS).
- Whipple's triad establishes a diagnosis of hypoglycemia: neuroglycopenic/autonomic symptoms, blood glucose <55 mg/dL, and prompt symptom resolution with glucose administration.
Diabetes Mellitus, Hypoglycemia & Metabolic Emergencies
Diagnostic Standards and Screening Algorithms for Diabetes Mellitus
Diabetes mellitus comprises a heterogenous group of metabolic disorders characterized by persistent hyperglycemia resulting from defects in insulin secretion, insulin action, or both. The American Diabetes Association (ADA) establishes strict, standardized laboratory thresholds for diagnosing diabetes mellitus and prediabetes.
Diagnostic Criteria for Diabetes Mellitus and Prediabetes
Screening should be initiated in all asymptomatic adults aged 35 years or older, or in adults of any age with an elevated Body Mass Index (BMI ≥25 kg/m², or ≥23 kg/m² in Asian Americans) who possess one or more additional risk factors (e.g., first-degree relative with diabetes, hypertension, physical inactivity, dyslipidemia). In the absence of unequivocal symptomatic hyperglycemia (e.g., polyuria, polydipsia, unexplained weight loss), a diagnosis requires two abnormal test results from the same sample or two separate test samples.
| Diagnostic Category | Fasting Plasma Glucose (FPG) | 2-Hour 75-g OGTT | Glycated Hemoglobin (HbA1c) | Random Plasma Glucose |
|---|---|---|---|---|
| Normal | <100 mg/dL (5.6 mmol/L) | <140 mg/dL (7.8 mmol/L) | <5.7% (39 mmol/mol) | N/A |
| Prediabetes | 100–125 mg/dL (5.6–6.9 mmol/L) | 140–199 mg/dL (7.8–11.0 mmol/L) | 5.7–6.4% (39–47 mmol/mol) | N/A |
| Diabetes Mellitus | ≥126 mg/dL (7.0 mmol/L) | ≥200 mg/dL (11.1 mmol/L) | ≥6.5% (48 mmol/mol) | ≥200 mg/dL + Symptoms |
[ Suspected Diabetes Mellitus ]
│
┌───────────────────────────────┴───────────────────────────────┐
[ Random Glucose ≥200 mg/dL + ] [ Asymptomatic Patient ]
[ Classic Symptoms (Polyuria) ] │
│ ┌────────────────┴────────────────┐
▼ [ Order FPG, HbA1c, or OGTT ] [ HbA1c <5.7% / FPG <100 ]
DIABETES CONFIRMED │ │
┌──────────────┴──────────────┐ ▼
[ Single Test Positive ] [ Two Tests Positive ] NORMAL (Re-screen 3 yr)
│ │
▼ ▼
[ Repeat Same or 2nd ] DIABETES CONFIRMED
[ Test on New Sample ]
│
┌───────┴───────┐
[ Positive ] [ Negative ]
│ │
▼ ▼
DIABETES RE-EVALUATE
Pharmacotherapeutic Management of Type 2 Diabetes Mellitus
The primary therapeutic objective in managing type 2 diabetes mellitus (T2DM) is achieving individualized glycemic control to prevent microvascular (retinopathy, nephropathy, neuropathy) and macrovascular complications. The general HbA1c target for non-pregnant adults is <7.0% (53 mmol/mol). However, a more stringent target of <6.5% is appropriate for younger patients with short disease duration and minimal hypoglycemia risk, whereas a relaxed target of <8.0% is indicated for patients with limited life expectancy, severe hypoglycemia history, or extensive comorbid conditions.
First-Line Therapy and Comorbidity-Driven Escalation
- Metformin: Biguanide that decreases hepatic gluconeogenesis and increases peripheral insulin sensitivity. Metformin does not cause hypoglycemia or weight gain. Common side effects are gastrointestinal distress (nausea, diarrhea). It is contraindicated when eGFR is <30 mL/min/1.73m² due to the risk of lactic acidosis. Dose reduction is recommended if eGFR falls between 30 and 45 mL/min/1.73m².
- SGLT2 Inhibitors (Empagliflozin, Dapagliflozin, Canagliflozin): Inhibit sodium-glucose cotransporter 2 in the renal proximal convoluted tubule, promoting glucosuria. They are indicated independently of baseline HbA1c in patients with heart failure (HFrEF/HFpEF), chronic kidney disease (eGFR ≥20–25 mL/min/1.73m² with albuminuria), or established Atherosclerotic Cardiovascular Disease (ASCVD). Adverse effects include mycotic genital infections, urinary tract infections, volume depletion/hypotension, and euglycemic DKA.
- GLP-1 Receptor Agonists (Semaglutide, Liraglutide, Dulaglutide): Incretin mimetics that enhance glucose-dependent insulin secretion, suppress glucagon release, and delay gastric emptying. Preferred in patients with established ASCVD, indicators of high cardiovascular risk, or where weight loss is a primary goal. Adverse effects include nausea, vomiting, diarrhea, and a risk of acute pancreatitis. They are contraindicated in patients with a personal or family history of medullary thyroid carcinoma or MEN 2.
- DPP-4 Inhibitors (Sitagliptin, Linagliptin): Prevent degradation of endogenous incretins. Weight-neutral with low hypoglycemia risk, but saxagliptin and alogliptin carry a warning for increased heart failure hospitalization risk.
- Sulfonylureas (Glipizide, Glimepiride, Glyburide): Stimulate pancreatic beta-cell insulin secretion by closing ATP-sensitive potassium channels. Associated with weight gain and significant hypoglycemia risk. Glyburide has active renal metabolites and should be avoided in renal impairment.
- Insulin Regimens: Initiated when HbA1c is severely elevated (>10% or blood glucose ≥300 mg/dL) or when oral agents fail. Basal insulin (glargine, degludec) provides 24-hour coverage, supplemented by prandial rapid-acting insulin (lispro, aspart) before meals.
Hyperglycemic Emergencies: DKA vs. HHS
Diabetic Ketoacidosis (DKA) and Hyperosmolar Hyperglycemic State (HHS) represent catastrophic, life-threatening metabolic crises resulting from insulin deficiency and counter-regulatory hormone excess (glucagon, cortisol, catecholamines, growth hormone).
| Clinical Characteristic | Diabetic Ketoacidosis (DKA) | Hyperosmolar Hyperglycemic State (HHS) |
|---|---|---|
| Primary Patient Population | Type 1 Diabetes Mellitus (can occur in T2DM) | Type 2 Diabetes Mellitus (elderly, nursing home) |
| Plasma Glucose | >250 mg/dL (typically 300–600 mg/dL) | >600 mg/dL (frequently >1000 mg/dL) |
| Arterial pH | <7.30 (Severe DKA: <7.00) | >7.30 |
| Serum Bicarbonate | <18 mEq/L (Severe DKA: <10 mEq/L) | >18 mEq/L |
| Anion Gap | >12 mEq/L (High Anion Gap Acidosis) | Normal or slightly elevated (<12 mEq/L) |
| Serum/Urine Ketones | Strongly Positive (Beta-hydroxybutyrate) | Absent or minimal |
| Effective Serum Osmolality | Variable (<320 mOsm/kg) | >320 mOsm/kg |
| Neurologic Status | Alert to drowsy; Kussmaul breathing | Severe lethargy, stupor, coma, focal deficits |
Stepwise Protocol for DKA and HHS Management
- Fluid Resuscitation: Infuse 0.9% Normal Saline at 10–20 mL/kg/hr (1–1.5 L during the 1st hour) to restore intravascular volume. Switch to 0.45% NS if corrected sodium is normal or high. When blood glucose drops to ≤200 mg/dL in DKA (or ≤300 mg/dL in HHS), add 5% Dextrose to IV fluids to allow continued IV insulin administration without triggering hypoglycemia or cerebral edema.
- Potassium Replacement: Check serum potassium prior to insulin initiation.
- If K⁺ <3.3 mEq/L: HOLD insulin. Administer IV KCl (20–30 mEq/hr) until K⁺ >3.3 mEq/L.
- If K⁺ 3.3–5.3 mEq/L: Administer IV KCl (20–30 mEq per liter of IV fluid) and initiate Regular Insulin drip.
- If K⁺ >5.3 mEq/L: Do not add potassium; start Regular Insulin drip and monitor K⁺ every 2 hours.
- Insulin Therapy: Continuous IV Regular Insulin drip at 0.1 units/kg/hr. Do not give a bolus if potassium is low. Resolution of DKA requires glucose <200 mg/dL AND two of the following: serum bicarbonate ≥15 mEq/L, venous pH >7.30, or anion gap ≤12 mEq/L.
Hypoglycemia & Endogenous Hyperinsulinism
Hypoglycemia is defined clinically by Whipple's triad: (1) symptoms consistent with hypoglycemia (autonomic: tremor, palpitations, diaphoresis; neuroglycopenic: confusion, seizures, altered mental status), (2) a documented low plasma glucose concentration (<55 mg/dL in non-diabetics), and (3) prompt relief of symptoms following glucose administration.
Differential Diagnosis of Hyperinsulinemic Hypoglycemia
When evaluating an adult without diabetes presenting with spontaneous hypoglycemia, serum insulin, C-peptide, proinsulin, and beta-hydroxybutyrate must be measured during a symptomatic episode or 72-hour fast.
| Parameter | Insulinoma | Exogenous Insulin Injection | Surreptitious Sulfonylurea Use |
|---|---|---|---|
| Serum Insulin | Elevated (>3 µIU/mL) | Extremely Elevated | Elevated (>3 µIU/mL) |
| Serum C-Peptide | Elevated (≥0.6 ng/mL) | Suppressed (<0.2 ng/mL) | Elevated (≥0.6 ng/mL) |
| Proinsulin | Elevated | Normal or Low | Elevated |
| Screen for Oral Hypoglycemics | Negative | Negative | Positive (Urine/Serum) |
A 24-year-old man with type 1 diabetes mellitus is brought to the emergency department due to nausea, abdominal pain, and confusion. Laboratory testing reveals a blood glucose of 420 mg/dL, serum sodium of 132 mEq/L, serum potassium of 3.1 mEq/L, serum bicarbonate of 10 mEq/L, and an arterial pH of 7.15. Urine is strongly positive for ketones. Which of the following is the most appropriate next step in management?
A 58-year-old woman with a 6-year history of type 2 diabetes mellitus returns for a routine follow-up. Her HbA1c is 8.2% despite adherent treatment with metformin 1,000 mg twice daily. She has a history of an anterior wall myocardial infarction 2 years ago. Her blood pressure is 128/78 mmHg, BMI is 31 kg/m², and eGFR is 68 mL/min/1.73m². Which of the following is the most appropriate agent to add to her current regimen?
A 34-year-old female nurse is evaluated for recurrent episodes of diaphoresis, tremulousness, and confusion that resolve after eating. During a supervised fast, her blood glucose drops to 42 mg/dL with concurrent neuroglycopenic symptoms. Laboratory evaluation during the episode reveals a serum insulin level of 28 µIU/mL (elevated), a serum C-peptide level of 0.1 ng/mL (suppressed), and a negative urine screening for sulfonylureas. Which of the following is the most likely diagnosis?