Electroencephalography shows no clear abnormalities in stage 0, even if minimal HE is present; in stages I, II and III there are triphasic waves over the frontal lobes that oscillate at 5 Hz, and in stage IV there is slow delta wave activity. However, the changes in EEG are not typical enough to be useful in distinguishing hepatic encephalopathy from other conditions.Once the diagnosis of encephalopathy has been made, efforts are made to exclude underlying causes (such as listed above in "causes"). This requires blood tests (urea and electrolytes, full blood count, liver function tests), usually a chest X-ray, and urinalysis. If there is ascites, a diagnostic paracentesis (removal of a fluid sample with a needle) may be required to identify spontaneous bacterial peritonitis (SBP). Classification
West Haven criteria
The severity of hepatic encephalopathy is graded with the West Haven Criteria; this is based on the level of impairment of autonomy, changes in consciousness, intellectual function, behavior, and dependence on therapy. Grade 0 - No obvious changes other than a potentially mild decrease in intellectual ability and coordination
Grade 1 - Trivial lack of awareness; euphoria or anxiety; shortened attention span; impaired performance of addition or subtraction
Grade 2 - Lethargy or apathy; minimal disorientation for time or place; subtle personality change; inappropriate behaviour
Grade 3 - Somnolence to semistupor, but responsive to verbal stimuli; confusion; gross disorientation
Grade 4 - Coma

Types
A classification of hepatic encephalopathy was introduced at the World Congress of Gastroenterology 1998 in Vienna.
Diet
In the past, it was thought that consumption of protein even at normal levels increased the risk of hepatic encephalopathy. This has been shown to be incorrect. Furthermore, many people with chronic liver disease are malnourished and require adequate protein to maintain a stable body weight. A diet with adequate protein and energy is therefore recommended.Dietary supplementation with branched-chain amino acids has shown improvement of encephalopathy and other complications of cirrhosis.Some studies have shown benefit of administration of probiotics ("healthy bacteria"). Lactulose/lactitol
Lactulose and lactitol are disaccharides that are not absorbed from the digestive tract. They are thought to decrease the generation of ammonia by bacteria, render the ammonia inabsorbable by converting it to ammonium (NH4+) ions, and increase transit of bowel content through the gut. Doses of 15-30 mL are typically administered three times a day; the result is aimed to be 3–5 soft stools a day, or (in some settings) a stool pH of <6.0. Lactulose may also be given by enema, especially if encephalopathy is severe. More commonly, phosphate enemas are used. This may relieve constipation, one of the causes of encephalopathy, and increase bowel transit.Lactulose and lactitol are beneficial for treating hepatic encephalopathy, and are the recommended first-line treatment. Lactulose does not appear to be more effective than lactitol for treating people with hepatic encephalopathy. Side effects of lactulose and lactitol include the possibility of diarrhea, abdominal bloating, gassiness, and nausea. In acute liver failure, it is unclear whether lactulose is beneficial.