Fatty Liver (cont.)
In this Article
What are the difficulties in evaluating NAFLD and NASH?
To make the diagnosis
of NAFLD or NASH, the doctor must fully consider the possible role of alcohol in
the patient's liver disease. This consideration requires detailed interviewing
of the patient. The patient must also be honest in reporting alcohol use to the
doctor. Unfortunately, this is not always the case. Moreover, the quantity of
alcohol required to cause liver disease is debated. In fact, the amount varies
from one study to another and from one country to another, and also varies
widely according to individual rates of processing (metabolizing) the alcohol.
One unit of an alcoholic beverage contains 10 grams of alcohol (ethanol). A
unit is roughly equivalent to one 12-ounce bottle of beer (5% alcohol), one
4-ounce glass of wine (12% alcohol), or one 1-ounce shot of hard liquor (40%
alcohol). Most specialists would agree that at or above a consumption of 4
units/day in women and 6 units/day in men for at least a year, liver disease
(due to alcohol) is highly likely to occur. However, there are reports that as
little as 2 units/day in women and 4 units/day in men may be sufficient to
promote liver disease, including fatty liver. The issue is further complicated
by the possibility that in the setting of insulin resistance, even small
quantities of alcohol could promote liver disease.
Studies have shown conclusively that NASH is associated with increased liver
enzymes (transaminases). The importance of these elevations, however, can be
somewhat overestimated because of what is referred to in statistics as an
inclusion bias. That is, in most studies as well as in most clinical practice,
only patients with persistently elevated transaminases are selected (included)
for liver biopsies.
Some studies, however, have included patients for liver biopsies based on
other criteria than elevated liver enzymes. These studies showed that NASH can
be present on a liver biopsy in individuals with normal liver tests in up to 30%
of cases of NASH. Furthermore, the degree of liver damage in NASH does not
relate to (correlate with) the level of the liver enzymes. (Chronic HCV
infection is another situation in which liver enzyme levels do not correlate
with the severity of disease.) Moreover, a fatty liver alone can produce
increased liver enzymes, even high elevations.
Among healthy individuals, liver enzyme levels are significantly higher in
those with a BMI greater than 23kg/m2 as compared to those with a BMI less than
23kg/m2. This difference suggests that the upper limit of normal for liver
enzymes should be adjusted according to the BMI.
All factors considered, NASH certainly cannot be diagnosed based just on a
finding of abnormal liver enzymes and signs of a fatty liver on ultrasound.
Furthermore, the exclusion of patients for liver biopsy on the basis of normal
liver enzymes will invariably exclude potential cases of NASH.
Next: What are the diagnostic clues for severe NASH? »
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