This is an auto-immune antibody (Ab) screening test in the IgG class.  Any titer that is reactive at a lesser dilution than 1:40 is considered a "negative" test result. A reactive test at dilutions between 1:40 and 1:80 is considered to be an indeterminate test result. If reactive at serum dilutions higher than 1:80, the antibody levels are considered to be abnormally elevated. [warning]

Situations Having Negative, Nonreactive, Undetected, or Subthreshold Levels of Ab:

• "negative" is failure of the test to reactive positively (non-reactive [NR]) at a 1:10 dilution of serum.
• "negative" may be where Ab has not yet risen to detectability; patient may have auto-immune disease but so early in its evolution that the antibodies are not detectible (so-called sub-clinical disease) OR not reactive above the conventional threshold level of "greater than 1:80"
• "negative" may be treated disease in which antibody level (titer) has dropped back below the reactive level of detectability.
• "negative" because no auto-immune skeletal muscle disease

• 30% of cases of myasthenia gravis have values higher than 1:80
• 95% of cases of myasthenia gravis AND  thymoma have values higher than 1:80
• 25% of cases of thymoma alone have values higher than 1:80

Other names for this exact or approximate agent are:   

• skeletal muscle antibodies