Hi Sad,
The normal is a range of 10-80 ug/dl (ug = micrograms)
Ammonia levels rise when there are large amounts of protein being catabolized and the liver is unable for some reason to convert it into urea so it can be excreted through the kidneys. Anything that interferes with the breakdown of ammonia in the system will increase serum levels.
Hope your Brother is doing well.
Penny