Diabetic Ketoacidosis and Hyperosmolar Hyperglycemic State

Biochemical Distinctions

• The American Diabetes Association notes that DKA is characterized by plasma glucose typically >250 mg/dL, while HHS presents with plasma glucose markedly elevated at >600 mg/dL 1
• The American Diabetes Association recommends that arterial pH ranges from <7.0 to 7.30 in DKA, with serum bicarbonate ≤18 mEq/L, whereas in HHS, arterial pH >7.30 with serum bicarbonate >15 mEq/L 1
• DKA is associated with strongly positive urine and serum ketones due to unregulated lipolysis and ketogenesis from severe insulin deficiency, as stated by the American Diabetes Association 1
• HHS is characterized by small or negative ketones, as residual insulin is adequate to prevent lipolysis and ketogenesis but insufficient to control hyperglycemia, according to the American Diabetes Association 1
• The effective serum osmolality is variable in DKA, but markedly elevated in HHS >320 mOsm/kg, driving the severe hyperosmolar state, as noted by the American Diabetes Association 1
• The anion gap is elevated (>10-12 mEq/L) in DKA due to accumulation of ketoacids, but variable and typically not significantly elevated in HHS, as stated by the American Diabetes Association 1

Clinical Presentation Differences

• DKA evolves rapidly, typically within 24 hours, allowing for acute presentation with minimal warning, according to the American Diabetes Association 2, 3
• HHS develops insidiously over several days to weeks, reflecting the slower progression of severe dehydration, as noted by the American Diabetes Association 2, 3
• Patients with DKA range from alert to drowsy, with stupor/coma only in severe cases, while stupor and coma are much more frequent in HHS, correlating with the degree of hyperosmolality, as stated by the American Diabetes Association 1, 2
• Kussmaul respirations (deep, rapid breathing) are characteristic of DKA, representing respiratory compensation for metabolic acidosis, but are absent in HHS due to lack of significant acidosis, according to the American Diabetes Association 2, 3
• Abdominal pain and vomiting occur in up to 25% of patients with DKA, sometimes with coffee-ground emesis from hemorrhagic gastritis, but abdominal pain is not a typical feature of HHS, as noted by the American Diabetes Association 2, 3

Pathophysiologic Mechanisms

• DKA is triggered by absolute or near-absolute insulin deficiency combined with elevated counterregulatory hormones, leading to uncontrolled lipolysis and ketone body production, as stated by the American Diabetes Association 1
• HHS is characterized by residual beta-cell function providing enough insulin to suppress lipolysis and prevent ketogenesis, but remaining inadequate to facilitate peripheral glucose utilization, according to the American Diabetes Association 1
• Moderate dehydration occurs in DKA from osmotic diuresis, while profound dehydration is the hallmark of HHS, often more severe than in DKA, contributing to the higher mortality, as noted by the American Diabetes Association 4

Mortality and Prognosis

• The mortality rate for DKA is approximately 5% in experienced centers, with lower rates in younger patients, according to the American Diabetes Association 3
• The mortality rate for HHS remains significantly higher at approximately 15%, reflecting the older age of patients, greater comorbidity burden, and severity of hyperosmolality, as stated by the American Diabetes Association 3
• Both conditions have worse outcomes at extremes of age (>65 years), in the presence of coma, hypotension, and hypothermia, as noted by the American Diabetes Association 4, 3

Common Pitfalls

• Euglycemic DKA can occur with SGLT2 inhibitors, causing DKA with glucose levels <250 mg/dL, potentially delaying diagnosis if clinicians rely solely on glucose thresholds, as stated by the American Diabetes Association 5
• Hypothermia is a poor prognostic sign, indicating peripheral vasodilation and potentially masking infection, according to the American Diabetes Association 2, 1

Biochemical and Clinical Distinctions Between Diabetic Ketoacidosis (DKA) and Hyperosmolar Hyperglycemic State (HHS)

Biochemical Distinctions

• Glucose thresholds differ markedly: DKA is typically associated with plasma glucose > 250 mg/dL, whereas HHS presents with plasma glucose > 600 mg/dL. 6
• Acid‑base profile: DKA shows arterial pH < 7.30 (often 7.0–7.30) and serum bicarbonate ≤ 18 mEq/L; HHS usually has arterial pH > 7.30 with bicarbonate > 15 mEq/L. 6
• Anion gap: DKA characteristically has an elevated anion gap (>10–12 mEq/L) due to ketoacid accumulation; the anion gap in HHS is variable and generally not markedly elevated. 6
• Ketone presence: Strongly positive urine and serum ketones are a hallmark of DKA, reflecting unregulated lipolysis and ketogenesis; HHS shows minimal or absent ketones because residual insulin suppresses lipolysis. 6
• Serum osmolality: Effective serum osmolality is markedly elevated (>320 mOsm/kg) in HHS, whereas it is variable in DKA. 6

Pathophysiologic Mechanisms

• DKA mechanism: Absolute or near‑absolute insulin deficiency combined with elevated counter‑regulatory hormones triggers uncontrolled lipolysis, free‑fatty‑acid release, hepatic fatty‑acid oxidation to β‑hydroxybutyrate and acetoacetate, leading to ketonemia and metabolic acidosis. 6
• HHS mechanism: Residual β‑cell function provides enough insulin to suppress lipolysis (preventing ketogenesis) but insufficient to promote peripheral glucose utilization, resulting in extreme hyperglycemia and hyperosmolarity. The evidence supporting this mechanism is considered weak. 6
• Shared metabolic consequence: Both DKA and HHS cause glycosuria‑induced osmotic diuresis with loss of water, sodium, potassium, and other electrolytes. 6

Clinical Presentation Differences

• Onset speed: DKA evolves rapidly, usually within 24 hours, leading to an acute presentation; HHS develops insidiously over several days to weeks. 6
• Mental status: Altered mental status ranging from alert to drowsy is common in DKA, with stupor/coma only in severe cases; stupor and coma are much more frequent in HHS, correlating with higher serum osmolality. 6
• Respiratory pattern: Kussmaul respirations (deep, rapid breathing) are characteristic of DKA as a compensatory response to metabolic acidosis; they are absent in HHS. 6
• Gastrointestinal symptoms: Up to 25 % of DKA patients experience abdominal pain and vomiting (occasionally with coffee‑ground emesis); abdominal pain is not typical in HHS. 6
• Shared signs: Polyuria, polydipsia, polyphagia, weight loss, dehydration, weakness, poor skin turgor, tachycardia, and hypotension occur in both conditions. 6
• Temperature reliability: Patients may be normothermic or hypothermic despite infection; temperature is an unreliable indicator of infection in both DKA and HHS. 6

Precipitating Factors

• Common precipitant: Infection is the leading trigger for both DKA and HHS, accounting for 30–50 % of cases. 6
• Other shared triggers: Cerebrovascular accident, myocardial infarction, pancreatitis, trauma, and drugs that affect carbohydrate metabolism (e.g., corticosteroids, thiazides, sympathomimetic agents). 6
• DKA‑specific triggers: New‑onset type 1 diabetes or inadequate insulin therapy in established type 1 diabetes. 6
• HHS‑specific triggers: Elderly individuals with new‑onset diabetes (especially those in long‑term care facilities) or inability to access fluids during hyperglycemia. 6

Diagnostic and Management Pitfalls

• Euglycemic DKA: Use of SGLT2 inhibitors can precipitate DKA with glucose < 250 mg/dL, potentially delaying diagnosis if clinicians rely solely on hyperglycemia thresholds. 6
• Overlap syndromes: Mixed presentations with features of both ketoacidosis and hyperosmolarity can occur, complicating diagnosis and management. 6