Hyperosmolar hyperglycemic state

Hyperosmolar hyperglycemic state is an acute metabolic emergency of diabetes characterized by extreme hyperglycemia, marked hyperosmolality, profound water depletion, and neurologic impairment of variable severity, without significant ketoacidosis or with only a mild ketotic component. Unlike diabetic ketoacidosis, in which the pathophysiologic core is massive production of ketone bodies due to overt insulin deficiency, hyperosmolar hyperglycemic state generally retains enough insulin activity to limit lipolysis and ketogenesis, but not enough to control hepatic glucose production and peripheral glucose utilization. The resulting clinical injury depends primarily on the combination of progressive dehydration, increased plasma tonicity, reduced organ perfusion, hemoconcentration, and cerebral, cardiovascular, and renal vulnerability.

From an epidemiologic standpoint, this crisis is less common than diabetic ketoacidosis but retains a higher mortality rate, chiefly because it more often affects older, frail people with type 2 diabetes mellitus, cardiovascular or renal comorbidities, severe infections, cognitive deficits, or limited ability to manage hydration and treatment independently. A substantial proportion of cases represent the first manifestation of previously undiagnosed diabetes, whereas in other patients the hyperosmolar state develops on a background of known but chronically uncontrolled diabetes. Attention to mixed forms has increased in recent years because elements of hyperosmolar hyperglycemic state and diabetic ketoacidosis often coexist, requiring more accurate assessment than the former rigid distinction between the two syndromes. In adults, the 2024 consensus report confirms that mortality from hyperosmolar state remains five to ten times higher than from diabetic ketoacidosis, while contemporary series report worse outcomes particularly in the presence of sepsis, organ failure, thrombosis, hypotension, and diagnostic delay.

The etiologic basis of hyperosmolar hyperglycemic state is a combination of relative insulin deficiency, increased counterregulatory hormones, and inability to compensate for massive hyperglycemia-induced urinary water loss through adequate fluid intake. In the great majority of cases, the setting is type 2 diabetes mellitus, often in older people with an impaired thirst response, functional disability, cognitive impairment, institutionalization, or limited access to fluids. In other cases, it is the initial presentation of previously unknown diabetes, sometimes in relatively young individuals already affected by severe insulin resistance or a major intercurrent illness. The most common precipitating causes are infections, pneumonia, sepsis, urinary tract infections, cerebrovascular events, acute myocardial infarction, pancreatitis, trauma, surgery, discontinuation or marked reduction of glucose-lowering therapy, glucocorticoids, diuretics, atypical antipsychotics, parenteral nutrition, and, more generally, any condition that increases the glucose load or reduces the ability to rehydrate spontaneously.

The pathophysiology begins when relative insulin deficiency becomes sufficient to prevent normal peripheral glucose uptake and leaves hepatic glucose production through glycogenolysis and gluconeogenesis unchecked. Glucagon, cortisol, catecholamines, and growth hormone accentuate this metabolic imbalance, but residual insulin generally continues to inhibit adipocyte lipolysis and hepatic ketogenesis. Blood glucose therefore rises markedly, while production of beta-hydroxybutyrate and acetoacetate remains modest or at least does not reach the level typical of diabetic ketoacidosis. This creates a clear pathophysiologic divergence: the syndrome is dominated by extreme hyperglycemia and its osmotic consequences, not by ketoacidosis.

When blood glucose greatly exceeds the renal threshold, intense osmotic diuresis develops. The kidneys excrete large amounts of glucose along with water, sodium, potassium, chloride, phosphate, and other solutes. During the initial stages, patients may partly compensate through polydipsia, but if fluid intake cannot keep pace with losses, or if access to water is limited, dehydration progresses to levels much more profound than those generally observed in diabetic ketoacidosis. Reduced intravascular volume lowers glomerular filtration and therefore reduces glucose excretion, further aggravating hyperglycemia. A vicious cycle develops in which volume depletion drives hyperglycemia and hyperglycemia drives volume depletion.

The progressive increase in effective osmolality is the central pathophysiologic event. Extracellular glucose draws water from the intracellular compartment, causing diffuse cellular dehydration. The brain is particularly vulnerable to this phenomenon. Loss of intracellular water from neurons and glial cells impairs synaptic function, alters the level of consciousness, and promotes lethargy, disorientation, seizures, and, in extreme cases, coma. Because corrected sodium tends to rise as free-water loss exceeds sodium loss, hypernatremia also contributes to elevated tonicity and neurologic dysfunction. Relative cerebral hypoperfusion, blood hyperviscosity, and a systemic inflammatory state add to these effects.

Hyperosmolar hyperglycemic state also causes severe hemorheologic impairment. Hemoconcentration increases blood viscosity, promotes microcirculatory stasis, and contributes to thrombotic risk, which is clinically more relevant than in diabetic ketoacidosis. Deep vein thrombosis, pulmonary embolism, arterial ischemic events, mesenteric ischemia, and stroke may be either complications or precipitating causes, making clinical reasoning particularly complex. At the renal level, severe dehydration readily causes prerenal acute kidney injury, sometimes aggravated by acute tubular necrosis if hypoperfusion is prolonged or nephrotoxic agents are also present.

A crucial point is that a pure hyperosmolar state exists, but mixed HHS-DKA presentations are common in clinical practice. The 2024 consensus report emphasizes that more than one-third of hyperglycemic crises may have overlapping features. This occurs when the water depletion and hyperosmolality typical of the hyperosmolar state are accompanied by metabolically significant ketosis and acidosis. In these patients, pathophysiology is not simply a linear sum of the two conditions, but a dynamic interaction among more severe insulin deficiency, profound hypoperfusion, hormonal stress, and reduced renal ability to eliminate both glucose and organic acids.

In pediatric patients, the condition is rarer but potentially even more dangerous. It may occur especially in adolescents with obesity and type 2 diabetes, but also in newly diagnosed type 1 diabetes or mixed presentations. Severe hyperosmolality, profound dehydration, and overly rapid correction of osmotic variables expose these patients to a high risk of thrombosis, rhabdomyolysis, kidney failure, pancreatitis, and brain injury. Pediatric protocols therefore emphasize intensive monitoring and controlled correction of osmolality even more than correction of blood glucose alone.

Hyperosmolar hyperglycemic state generally develops more insidiously than diabetic ketoacidosis. The history often reveals days or weeks of progressive deterioration with polyuria, polydipsia, weight loss, worsening fatigue, blurred vision, reduced appetite, and a progressive inability to maintain adequate hydration. In many older patients, the history is incomplete because cognitive impairment, drowsiness, or confusion prevents reliable reporting; in these cases, family members or caregivers report increased thirst, worsening general condition, reduced fluid intake, incontinence, immobilization, or the development of fever and cough.

The neurologic component is often the most evident feature. Patients may present with psychomotor slowing, disorientation, stupor, incoherent speech, paradoxical agitation, transient focal deficits, seizures, or coma. The degree of neurologic disturbance depends primarily on the severity of hyperosmolality and how rapidly it developed. There is no perfect correlation, however, between a single osmolality value and the clinical picture because age, cerebral vulnerability, sodium, perfusion, and associated diseases modify the presentation. This variability means that not every neurologic abnormality should automatically be attributed to the hyperosmolar state: stroke, central nervous system infection, a primary seizure, or subdural hematoma may coexist or represent the precipitating cause.

Physical examination is dominated by signs of severe volume depletion. The mucous membranes are dry, skin turgor is reduced, the eyes are sunken, heart rate is increased, and blood pressure is often low or frankly unstable in advanced cases. Body temperature may be elevated with infection, but even significant sepsis may occur without fever in frail older patients. Urine output may initially appear preserved or increased, but decreases as hypovolemia and glomerular filtration worsen. Breathing does not usually show the Kussmaul pattern typical of diabetic ketoacidosis because significant acidosis is absent by definition; if deep breathing, intense nausea, vomiting, and abdominal pain are observed, a mixed presentation with a ketoacidotic component should be suspected.

Abdominal pain is less typical than in diabetic ketoacidosis, whereas extreme weakness, inability to stand, deterioration of functional independence, and symptoms related to the precipitating event—such as productive cough, dysuria, chest pain, hemiparesis, fever, or an acute abdomen—are more common. In institutionalized or dependent patients, hyperosmolar state may be recognized late because hyperglycemia accumulates on a background already marked by frailty, limited access to water, diuretic medications, or reduced perception of thirst.

An important clinical feature is the frequent absence of classic signs that, in the medical imagination, immediately suggest an acute diabetic crisis. Acetone-like breath, marked abdominal pain, and Kussmaul breathing may be entirely absent. This makes the hyperosmolar state a sometimes less dramatic but more insidious syndrome. The real risk is that it will be mistaken for simple dehydration, delirium in an older person, sepsis without recognition of the metabolic component, or a primary neurologic condition. Blood glucose should in fact be measured systematically in every patient with altered mental status and signs of dehydration specifically to avoid missing this diagnosis.

After clinical suspicion arises, the diagnostic pathway must answer three fundamental questions: whether the patient truly has a hyperosmolar hyperglycemic state, whether there is overlap with diabetic ketoacidosis, and what the precipitating factor is. Initial investigations include plasma glucose, a complete electrolyte panel, creatinine, blood urea nitrogen, blood gas analysis, measured or calculated osmolality, blood beta-hydroxybutyrate, urinalysis, complete blood count, electrocardiogram, and continuous monitoring of vital signs. Beta-hydroxybutyrate measurement is important even in hyperosmolar state because it distinguishes a pure presentation from a mixed form. Sodium must always be interpreted in the context of hyperglycemia and corrected because the measured value may underestimate the true extent of free-water loss.

Modern diagnosis is based on the simultaneous presence of marked hyperglycemia, significant hyperosmolality, absence of substantial ketosis, and absence of clinically relevant metabolic acidosis. The 2024 consensus report emphasizes that every component must be present to define the condition as a pure hyperosmolar hyperglycemic state. If elevated ketonemia, low pH, or low bicarbonate is present, the framework of pure hyperosmolar state no longer applies and an overlapping ketoacidotic presentation must be recognized. This diagnostic step is crucial because it influences monitoring intensity, the pace of insulin therapy, and priorities for correction.

According to the 2024 consensus report in adults, diagnosis of hyperosmolar hyperglycemic state requires very high blood glucose, effective osmolality or calculated total osmolality above the diagnostic threshold, absence of significant acidosis, and absence of marked ketosis. Reviews derived from this document and subsequent educational summaries consistently report a glucose threshold of at least 600 mg/dL, effective osmolality above 300 mOsm/kg or total osmolality above 320 mOsm/kg; absence of acidosis is defined by pH of at least 7.3 and bicarbonate of at least 15 mmol/L, with beta-hydroxybutyrate below 3 mmol/L or only minimal urine ketone positivity.

Official diagnostic criteria for hyperosmolar hyperglycemic state

• Plasma glucose ≥600 mg/dL
• Effective osmolality >300 mOsm/kg or total osmolality >320 mOsm/kg
• Absence of significant ketosis, with beta-hydroxybutyrate <3.0 mmol/L or absent to only mildly positive urine ketones
• Absence of significant acidosis, with pH ≥7.3 and bicarbonate ≥15 mmol/L

Diagnostic evaluation does not end with labeling the crisis. Sepsis, myocardial infarction, stroke, pancreatitis, bleeding, acute kidney injury, precipitating medications, and possible thrombosis must be identified. Depending on the context, investigations therefore include chest radiography, blood cultures, urine culture, troponin, lipase, coagulation studies, lactate, inflammatory markers, and neuroimaging. In patients with marked neurologic impairment, brain computed tomography is justified when the presentation is not consistent with hyperosmolality alone, when focal signs are present, or when an acute cerebrovascular event is suspected. In older people, the home medication list should also always be reassessed because diuretics, glucocorticoids, antipsychotics, and drugs that interfere with thirst perception may have played an important pathogenic role.

The differential diagnosis includes diabetic ketoacidosis, mixed HHS-DKA presentations, hypernatremia from other causes, acute kidney injury with uremia, sepsis-associated encephalopathy, stroke, nonconvulsive status epilepticus, drug toxicity, and other causes of altered mental status. The most dangerous error is to regard extreme hyperglycemia as the sole diagnostic element. Correct diagnosis always requires integrated interpretation of blood glucose, osmolality, ketonemia, pH, bicarbonate, mental status, and the clinical context.

Resolution cannot be declared on the basis of falling blood glucose alone. According to the 2024 consensus report, hyperosmolar state is considered resolved when serum osmolality falls below 300 mOsm/kg, urine output exceeds 0.5 mL/kg/hour, the patient regains an adequate level of consciousness, and blood glucose falls below 250 mg/dL. These criteria are important because they emphasize that the primary therapeutic objective is not merely to lower glucose, but to correct hyperosmolality and volume depletion safely.

Treatment of hyperosmolar hyperglycemic state follows a different hierarchy from that of diabetic ketoacidosis. The absolute priority is correction of dehydration and hyperosmolality, while insulin, although necessary, is introduced more cautiously and often after volume expansion has begun. The initial objective is to restore tissue perfusion, improve glomerular filtration, facilitate renal glucose clearance, and gradually reduce plasma tonicity without causing abrupt water shifts between compartments. In adults, crystalloids—generally normal saline or other appropriate crystalloid solutions—are used, with rate and volume adjusted according to blood pressure, heart rate, kidney function, cardiac comorbidities, and corrected sodium. The 2024 consensus report emphasizes that the rate of glucose and osmolality reduction must be controlled because overly rapid correction may cause neurologic complications.

Continuous intravenous insulin is indicated in critical cases and mixed presentations, but in pure hyperosmolar state it is generally started after fluid therapy has already produced initial hemodynamic and metabolic improvement. This is because glucose may fall substantially with rehydration alone in patients with HHS, and overly early or aggressive insulin could lower osmolality rapidly, increasing the risk of brain injury or hemodynamic collapse. When blood glucose approaches 250–300 mg/dL, glucose is added to the intravenous fluids not because the crisis has ended, but to allow treatment to continue until hyperosmolality is fully corrected and neurologic recovery occurs.

Management of electrolytes is crucial. Total-body potassium is generally reduced by urinary losses even when the initial serum concentration appears normal or elevated. Serial monitoring is therefore mandatory, and replacement is adjusted to the starting value, kidney function, and urine output. Phosphate and magnesium should also be reassessed, especially in patients with muscle weakness, arrhythmias, respiratory failure, or rhabdomyolysis. Bicarbonate has no role in pure hyperosmolar state precisely because significant metabolic acidosis should be absent by definition; if substantial acidosis is present, the presentation should be reassessed as a mixed form or another cause should be sought, such as hypoperfusion-related lactic acidosis or kidney failure.

An essential part of treatment is identifying and managing the precipitating cause. Infections require appropriate antimicrobial therapy, myocardial infarction and stroke require their dedicated specialist pathways, pancreatitis requires targeted management, and treatment discontinuation or iatrogenic drugs require immediate correction. Medication review is often decisive in frail older patients because diuretics may aggravate free-water loss, glucocorticoids amplify hyperglycemia, and antipsychotics may contribute both to poor glycemic control and reduced fluid intake. Thromboembolism prophylaxis should also be planned according to risk and clinical setting because hyperosmolality and hemoconcentration clearly increase the likelihood of thrombotic events.

Monitoring must be close and serial. Blood glucose, sodium, potassium, creatinine, mental status, osmolality, and urine output guide therapy in real time. The desired course is not an abrupt fall in glucose, but a gradual and safe reduction accompanied by restored perfusion, improved consciousness, and a progressive decline in tonicity. In mixed HHS-DKA presentations, treatment should follow diabetic ketoacidosis principles for insulin and correction of ketosis, without losing sight of the specific risk posed by hyperosmolality.

Prognosis depends largely on age, comorbidities, diagnostic promptness, the precipitating cause, and development of thrombotic, neurologic, or renal complications. Even when metabolic correction is technically well performed, hyperosmolar hyperglycemic state remains a high-mortality syndrome because it often develops in patients who are already biologically frail. At the same time, an important part of long-term prognosis is modifiable: every episode should conclude with redefinition of glucose-lowering therapy, education on early recognition of dehydration and sick-day management, review of concomitant medications, verification of access to fluids and therapeutic supplies, and involvement of the family or care network.

The most immediate and consistent complication of hyperosmolar hyperglycemic state is circulatory failure due to severe dehydration. Free-water loss may be enormous and result in hypotension, shock, reduced coronary and cerebral perfusion, acute kidney injury, and hypoperfusion-related lactic acidosis. Unlike diabetic ketoacidosis, the depth of volume depletion and degree of hyperosmolality often make this crisis more prolonged, less conspicuous at onset, and more damaging to organs.

Neurologic manifestations may be prominent, but they are not required for diagnosis. Altered consciousness, seizures, focal deficits, transient hemiparesis, severe delirium, and coma may occur. In some cases, the neurologic picture resolves completely as osmolality is corrected; in others, it reveals or promotes a structural event such as ischemic or hemorrhagic stroke. There is also a risk of brain injury from inappropriate correction of osmotic variables, especially if glucose and tonicity are lowered too rapidly. This issue is particularly critical in children and adolescents, in whom management must be even more cautious.

Thrombotic complications are a distinguishing feature of the hyperosmolar state. Hemoconcentration, hyperviscosity, immobility, and the inflammatory state promote deep vein thrombosis, pulmonary embolism, arterial ischemia, cerebral venous sinus thrombosis, mesenteric ischemia, and worsening of preexisting atherothrombotic disease. The literature and British guidelines emphasize that thrombotic risk is greater in hyperosmolar state than in diabetic ketoacidosis and must be explicitly incorporated into clinical reasoning and prophylaxis planning.

Other complications include acute kidney injury, rhabdomyolysis, pancreatitis, pulmonary edema during rehydration in patients with heart disease, severe electrolyte disturbances, and cardiac arrhythmias. Hypokalemia may develop during treatment if replacement is inadequate, while hypernatremia may persist or even become more apparent once hyperglycemia is corrected because the true extent of free-water loss emerges. In mixed presentations, risk expands further because complications of ketosis and acidosis are added to those of hyperosmolality.

A common but less visible complication is recurrence. Hyperosmolar state is almost never an isolated random event. It often signals prolonged poor glycemic control, social frailty, cognitive decline, inadequate home care, poor understanding of therapy, or the practical inability to maintain hydration and treatment. Secondary prevention must therefore go beyond medication prescribing and include education, caregiver support, review of the care environment, and strategies for febrile or gastrointestinal intercurrent illnesses.