In simple words: This code describes a severe confusional state brought on by a known medical problem.It's like a sudden and temporary state of disorientation and not being fully aware of what's going on. The specific medical problem causing the confusion is diagnosed separately.

Delirium due to known physiological condition refers to a state of extreme confusion and loss of awareness caused by brain damage due to a previously diagnosed disease or condition.It's characterized by disturbances in attention, awareness, and cognition that develop over a short period and fluctuate throughout the day. The provider must document the physiological cause, which should be coded first.

Example 1: A patient with a known history of heart failure presents to the emergency department with acute confusion, disorientation, and agitation. Lab tests reveal an electrolyte imbalance. The delirium is attributed to the heart failure causing metabolic derangement, so F05 is coded, with the heart failure diagnosis coded first., A patient with pneumonia develops sudden confusion, fluctuating levels of consciousness, and visual hallucinations. The delirium is deemed a direct consequence of the infection, leading to the use of code F05, with the pneumonia diagnosis coded first., A patient with a history of Parkinson’s disease experiences an episode of delirium after a medication adjustment, including disorientation, and difficulty with attention. The delirium is considered to be caused by the medication interacting with Parkinson's, so F05 is used, and the Parkinson's disease is coded first.

Documentation should clearly establish the cause-and-effect relationship between the physiological condition and the delirium. The underlying physiological condition should be clearly documented and coded as the primary diagnosis. The documentation should also detail the specific symptoms of delirium exhibited by the patient, such as confusion, disorientation, and altered level of consciousness.

** Differentiating delirium from other conditions such as dementia is crucial for accurate coding. Dementia has a slower onset and generally lacks the fluctuating pattern of delirium. If both delirium and dementia are present in a patient with a known physiological condition, the underlying condition should be coded first, then the F05, then F02.x or F03.x for dementia.