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Continuation of Diagnosing AutoImmune Hepatitis
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Melissa Palmer, MD posted:
Specific Autoimmune Blood Tests

Specific autoimmune blood tests include a check for elevated immunoglobulin levels, specifically an elevated gamma-globulin or immunoglobulin G (IgG) level. Gamma globulin or IgG levels greater than two times the upper limit of normal are highly suggestive of a diagnosis of AIH. In addition, the presence of antinuclear antibody (ANA), smooth muscle antibody (SMA), and the liver kidney microsomal antibody (anti-LKM) must be searched for. As mentioned previously, these antibodies are known as autoantibodies.
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Autoantibodies do not cause AIH. However, many autoantibodies are produced by the body in people with AIH. ANA and SMA are the most common, and are therefore, considered "markers" of AIH. It should be noted that both ANA and SMA are not specific for AIH. This means they may also occur in liver diseases other than AIH, as well as in diseases of other organs. Approximately 54 percent of people with AIH have both ANA and SMA present in their blood. Other people have one, but not both, of these autoantibodies. ANA occurs alone as a marker of AIH 13 percent of the time and SMA occurs alone as a marker 33 percent of the time. The presence of both autoantibodies is not necessary for the diagnosis to be made. To make things even more confusing - it is possible for people to lack all autoantibodies and still have AIH. This occurs in about 10 - 20 percent of people with AIH. These people are known as autoantibody-negative AIH (type III AIH). (See page xx). It has been found that one or both of these autoantibodies, although not present initially, may appear later in the course of the disease. This is of importance for people who initially test negative for the presence of autoantibodies and thus, have not been given a definitive diagnosis by their doctors.
When ANA and SMA are present in liver diseases other than AIH, their values tend to be very low and are thought to be of little significance. These autoantibodies are reported to doctors on blood work by dilution titers (the dilution of blood containing a specific antibody). A titer of 1:160 (one to one hundred sixty) or greater is considered a high titer and is highly suggestive of a diagnosis of AIH. Titers of less than 1:80 (one to eighty) are considered low titers and are not necessarily indicative of a diagnosis of AIH. Low titers are often found in other liver disorders and are usually not clinically significant. Note that autoantibody titers can fluctuate from one blood test to the next, and during therapy for AIH, they may disappear altogether. Moreover, the levels of these autoantibodies do not correlate with the severity or prognosis of disease.

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