F05

Delirium due to known physiological condition

Delirium due to a known physiological condition is an acute, fluctuating syndrome characterized by a disturbance in attention, awareness, and cognition that is not better explained by another preexisting or evolving neurocognitive disorder. This condition develops over a short period of time (typically hours to a few days) and represents a significant change from baseline. It is a direct physiological consequence of an underlying medical condition, such as systemic infection, metabolic imbalance, endocrine disorder, organ failure, or the effects of a medication or toxin. Clinically, it is often categorized by its psychomotor manifestations into hyperactive, hypoactive, or mixed subtypes. The hypoactive form is frequently underdiagnosed in clinical settings despite being associated with a poorer prognosis. Effective management requires the prompt identification and treatment of the primary underlying physiological driver, alongside supportive care to manage safety and sensory input.

Clinical Symptoms

  • Acute disturbance in attention (reduced ability to direct, focus, sustain, and shift attention)
  • Reduced clarity of awareness of the environment
  • Disorientation to time, place, or person
  • Memory impairment (especially short-term memory)
  • Fluctuating level of consciousness throughout the day
  • Visual or auditory hallucinations
  • Perceptual illusions or misinterpretations of environmental stimuli
  • Psychomotor agitation (restlessness, pulling at IV lines)
  • Psychomotor retardation (sluggishness, lethargy, or staring into space)
  • Reversal of the sleep-wake cycle (daytime somnolence, nighttime wakefulness)
  • Incoherent or rambling speech
  • Emotional lability (sudden shifts into fear, depression, or euphoria)
  • Paranoia or delusional thinking

Common Causes

  • Systemic infections (e.g., Urinary Tract Infection, Pneumonia, Sepsis)
  • Metabolic derangements (e.g., Hyponatremia, Hypercalcemia, Hypoglycemia)
  • Dehydration and electrolyte imbalances
  • Organ failure (e.g., Hepatic encephalopathy, Uremic encephalopathy)
  • Endocrine disorders (e.g., Hyperthyroidism, Adrenal crisis)
  • Acute neurological events (e.g., Ischemic stroke, Intracranial hemorrhage, Post-ictal states)
  • Postoperative complications or anesthesia recovery
  • Hypoxia or hypercapnia from respiratory failure
  • Medication toxicity (especially Anticholinergics, Benzodiazepines, and Opioids)
  • Withdrawal from alcohol or sedative-hypnotic substances
  • Thiamine deficiency (Wernicke Encephalopathy)

Documentation & Coding Tips

Explicitly link the delirium to the underlying physiological cause using causal language such as due to or secondary to.

Example: Patient is an 88-year-old female with acute onset of fluctuating consciousness and visual hallucinations. Lab work indicates a sodium level of 122 mEq/L. Assessment: Delirium due to severe hyponatremia (F05). The delirium is the primary reason for admission today, requiring constant 1-to-1 supervision and IV fluid correction.

Billing Focus: Documentation must specify the underlying physiological condition, as F05 cannot be coded as a standalone primary diagnosis without an associated medical etiology.

Document the acuity and the transient nature of the symptoms, distinguishing them from the patient's baseline cognitive status.

Example: The patient, who has a documented baseline of mild cognitive impairment, developed acute confusion and agitation following a hip arthroplasty. On examination, the patient is unable to follow simple commands and exhibits a waxing and waning level of alertness. Diagnosis: Post-operative delirium due to surgical stress and anesthesia (F05).

Billing Focus: Specifying that this is an acute change from baseline helps justify the use of higher-level E/M codes due to the increased risk of patient morbidity.

Describe specific behavioral disturbances and fluctuations in the sleep-wake cycle to support the diagnosis of F05.

Example: Patient exhibits nocturnal wandering, reversal of sleep-wake cycle, and acute paranoid ideation during evening hours (sundowning). These symptoms were not present prior to the onset of acute pneumonia. Diagnosis: Delirium due to bacterial pneumonia (F05).

Billing Focus: Detailed behavioral descriptions support the medical necessity for psychiatric consultation and specific CPT add-on codes for prolonged services if monitoring is required.

Include results from standardized screening tools such as the Confusion Assessment Method (CAM) to provide objective clinical evidence.

Example: Patient screened positive on CAM today with acute change in mental status, inattention, and disorganized thinking. CT head negative for acute CVA; however, urinalysis confirms leukocytosis. Final diagnosis: Delirium due to urinary tract infection (F05).

Billing Focus: Objective scoring provides audit-proof evidence for the diagnosis, supporting the selection of high-complexity MDM for hospital visits.

Distinguish between hyperactive and hypoactive delirium, as both are captured under F05 but have different clinical trajectories.

Example: Patient is in a state of hypoactive delirium characterized by profound lethargy, reduced psychomotor activity, and failure to respond to verbal stimuli, secondary to acute renal failure. This represents a significant deviation from his baseline alert state. Diagnosis: Delirium due to acute kidney injury (F05).

Billing Focus: Specifying the delirium subtype (hyperactive vs. hypoactive) assists in demonstrating the high complexity of the diagnostic process (MDM).

Relevant CPT Codes

Related Diagnoses

Hierarchy