The purpose of this blood serum test is to help detect and evaluate treatment of acute hepatic disease, especially hepatitis, and cirrhosis without jaundice. To help distinguish between mytyocardial (heart) and liver tissue damage (used with the AST enzyme test). Also to assess hepatotoxicity of some drugs.
The average wingspan for an NBA player (even normal 6'0 guys) is +4 inches. I think that around your height thing is just an estimate. For the general population, the average might be +2 inches.
Epstein et al state that proptosis is a globe that protrudes 18 mm or less and exophthalmos is protrusion of greater than 18 mm. The upper limit of normal was 21 mm. In adult white males, the average distance of globe protrusion is 16.5 mm, with the upper limit of normal at 21.7 mm.