Albumin and Globulin. These two are proteins found in the blood. Albumin is a smaller protein and is water soluble and Globulin is a larger protein and is usually not water soluble.

albumin is produced in the liver and is helps carry other substances( vitamins, minerals, lipids etc..) through the blood system.

globulin is produced by both the liver and the immune system. It's function is more complex.

Both are helpful in determining liver function, immune system function, as well as hydration, nutrition, they have complex and important roles in determining both current health and a predictor of possible future health.

In FIP, there are some that think they are the most current effective and easily accessible way of diagnosis.
the rule is albumin/globulin ratio >0.8 FIP not likely
albumin/globulin ratio <0.4FIP likely
between 0.4-0.8 look for other disease process.
You can read more about albumin and globulin here:
http://www.dr-addie.com/WhatIsFIP.htm#Diagnosis%20of%20FIP
I agree with some, not all of the information on this web site, but I do agree with the alb./glb information basically as it is presented.

Albumins and Globulins are complex in the bodies functioning and I am personally not sure that their roles in cat health are completely known or fully understood, because of their obvious link to nutrition. I do not think that the nutritional needs of cats are properly met by any commercial diets and certainly are not addressed properly in veterinary colleges which receive a great deal of funding from the producers of these commercial diets.