Hepatic encephalopathy (HE) is diagnosed primarily through clinical evaluation, not a single definitive test. There is no blood test or brain scan that confirms it on its own. Instead, doctors piece together your symptoms, medical history, physical exam findings, and lab work while ruling out other conditions that can look similar. The process differs depending on whether symptoms are obvious or subtle.
Covert vs. Overt: Two Different Diagnostic Challenges
Modern practice splits hepatic encephalopathy into two broad categories based on severity, and each one presents a different diagnostic puzzle. Overt HE involves visible, unmistakable symptoms: confusion, personality changes, slurred speech, or loss of consciousness. Covert HE is far subtler, involving slight problems with memory, concentration, or reaction time that you or your family might barely notice.
Overt HE is usually recognized at the bedside. Covert HE requires specialized testing to detect. Both matter clinically. Covert HE affects your ability to drive, work, and manage daily tasks, and it raises the risk of progressing to a full-blown episode. It is also classified further by cause: type A in people with acute liver failure, type B in those with abnormal blood vessel connections that bypass the liver, and type C in people with cirrhosis, which is by far the most common scenario.
The West Haven Criteria: Grading Severity
The most widely used tool for classifying HE is the West Haven Criteria, which grades symptoms on a scale from 0 to 4. This grading system helps doctors track how severe an episode is and whether it’s getting better or worse.
- Grade 0: Subtle changes in short-term memory, concentration, and reaction time. These may only be noticeable to you or people closest to you, and they typically show up only on formal neuropsychological tests.
- Grade 1: Mild confusion or forgetfulness, mood swings (euphoria or anxiety), difficulty with simple math, trouble with fine motor skills like handwriting, and a flipped sleep schedule where you’re awake at night and drowsy during the day.
- Grade 2: Clear personality changes, inappropriate or out-of-character behavior, lethargy, disorientation to time (not knowing the day or year), and slurred speech.
- Grade 3: Sluggish thinking and movement, disorientation to place (not knowing where you are), drowsiness, severe confusion or delirium, and involuntary twitching or tremors.
- Grade 4: Total loss of consciousness (coma).
Grades 0 and 1 fall under covert HE. Grades 2 through 4 are considered overt. Overt HE is further described by its pattern over time: episodic (a single bout), recurrent (two or more episodes within six months), or persistent (symptoms that never fully clear between episodes).
Physical Exam: Checking for Asterixis
One of the hallmark physical findings in hepatic encephalopathy is asterixis, sometimes called “liver flap.” It’s an involuntary, irregular jerking motion of the hands that signals the brain is struggling to maintain steady muscle control. To check for it, the doctor will ask you to extend both arms straight out in front of you, bend your wrists back, and spread your fingers wide with your eyes closed. If your wrists briefly flap or jerk downward, that’s a positive result. Gently pushing on the backs of your hands to increase the wrist angle makes the flap easier to detect.
Asterixis can also be checked in the legs by having you lie on your back, lift one leg, and hold the ankle bent upward. A sudden drop of the foot or a quick lowering of the leg counts as positive. This sign is most associated with grade 2 and grade 3 HE. It’s useful but not unique to liver disease; kidney failure and certain other metabolic problems can produce the same finding.
The Role of Blood Ammonia Levels
Ammonia testing is one of the most commonly ordered labs in suspected HE, but its role is more limited than many people assume. People with hepatic encephalopathy do have elevated blood ammonia levels, since the damaged liver can’t process ammonia efficiently. However, the severity of symptoms does not reliably track with ammonia numbers beyond a certain point. Someone with very high ammonia may have mild confusion, while someone with a moderately elevated level may be much more impaired.
Because of this poor correlation, current guidelines do not recommend using ammonia levels alone to diagnose HE. Where ammonia testing is most useful is in the opposite direction: if a blood ammonia level comes back completely normal, that should prompt your doctor to reconsider the diagnosis and look harder for other explanations for your symptoms.
Specialized Tests for Covert HE
Because covert hepatic encephalopathy doesn’t produce obvious symptoms, detecting it requires formal testing. The most established tool is the Psychometric Hepatic Encephalopathy Score (PHES), a set of five paper-and-pencil tests that measure different aspects of brain function. The battery includes tasks for connecting numbered dots in sequence (testing speed and attention), matching digits to symbols (testing processing speed), placing dots inside small circles (testing fine motor control), and tracing a line without crossing boundaries (testing coordination and precision). Results are compared against population norms adjusted for age and education.
A newer, more accessible option is the EncephalApp Stroop Test, a smartphone-based screening tool. It measures how quickly you can identify colors while ignoring conflicting information on screen, a task that requires the kind of focused attention and processing speed that covert HE impairs. In validation studies, a combined response time above 190 seconds identified covert HE with about 89% sensitivity and 82% specificity in people with cirrhosis. This makes it a practical screening option that can be done in a regular clinic visit without specialized equipment.
Brain Imaging and EEG
Brain scans like CT or MRI are not used to confirm hepatic encephalopathy itself. Their main purpose is to rule out other causes of altered mental status, particularly bleeding inside the skull or stroke, which require completely different treatment. If someone with liver disease suddenly becomes confused, imaging helps ensure nothing else is going on.
Electroencephalography (EEG), which records the brain’s electrical activity, shows characteristic changes as HE progresses. In early stages, the normal background rhythm gradually slows. As the condition worsens, the brain produces increasingly slow, high-amplitude waves. Some patients develop a pattern called triphasic waves, which are widespread, often most prominent over the front of the brain, and have a distinctive front-to-back timing sequence. In the most severe stage (coma), brain activity becomes suppressed, which generally carries a poor prognosis.
Triphasic waves were once considered a signature of hepatic encephalopathy specifically, but they’re now recognized as a nonspecific finding. Kidney failure, severe infections, and other metabolic disturbances can produce the same EEG pattern. So while EEG can support the diagnosis and help track severity, it can’t confirm HE on its own.
Ruling Out Conditions That Mimic HE
Because hepatic encephalopathy is largely a diagnosis of exclusion, especially in its overt form, your doctor needs to systematically rule out other causes of confusion or altered consciousness. The list of conditions that can mimic HE is long, and many of them are common in people who already have liver disease:
- Medication side effects: Sedatives, opioids, and other drugs that affect the brain, which people with liver disease may metabolize poorly.
- Electrolyte imbalances: Low sodium (hyponatremia) and high calcium are particularly common mimics.
- Kidney failure (uremia): Produces its own form of encephalopathy with very similar symptoms.
- Infections: Both systemic infections (like pneumonia or urinary tract infections) and central nervous system infections (like meningitis).
- Alcohol-related causes: Intoxication, withdrawal, or Wernicke-Korsakoff syndrome from severe vitamin B1 deficiency.
- Low blood sugar (hypoglycemia): Can cause confusion that resolves quickly once sugar levels are corrected.
- Carbon dioxide buildup (hypercapnia): Occurs in people with lung disease and produces drowsiness and confusion.
- Seizure activity: Nonconvulsive epilepsy can cause prolonged confusion without visible convulsions.
- Intracranial bleeding or stroke: Requires urgent imaging to identify.
This is why the diagnostic workup for HE typically includes basic blood chemistry, a complete blood count, infection screening, a medication review, and often brain imaging. The goal is to either identify and treat a different cause or confirm that no alternative explanation exists, leaving HE as the most likely diagnosis in someone with known liver disease.
What Triggers Are Looked For
Part of diagnosing an HE episode is identifying what set it off. Hepatic encephalopathy rarely appears without a precipitant, and finding the trigger is essential because treating it is often the fastest way to resolve the episode. Common triggers include infections (especially in the urinary tract, lungs, or abdominal fluid), gastrointestinal bleeding, constipation, dehydration, excessive dietary protein, electrolyte imbalances from diuretics, and use of sedatives or opioids. Doctors will record the identified precipitant, the severity grade, and whether there are any abnormal blood vessel shunts bypassing the liver, as all of these factors shape both the diagnosis and the treatment approach.