Amylase is a pancreatic enzyme. Zinc targets the pancreas and appears to cause damage resulting in elevated amylase levels. Amylase is included in our routine blood screens. Other causes of elevated amylase levels are dietary problems, infection, neoplasia, and degenerative conditions. Treatment for zinc toxicity involves removal of the offending source and chelation with either injectable or oral therapy depending on the severity of the signs.
Most birds recover well when treated promptly.
They require a very specific diet, strict temperature control, special ultraviolet-B lighting and proper humidity. When one of these is lacking or inappropriate levels are given then disease results. Unfortunately when a disease process is noted it is usually resulting from an imbalance that started months to years earlier. Your iguana may seem to thrive initially, then more or less reach a plateau. I recommend that all iguanas are examined at least once a year and routine bloodwork be run to identify problems.