The blood may be slightly thick with more red blood cells than normal (erythrocytosis). The white cells may be elevated (leukocytosis), but two types of white blood cells—lymphocytes and eosinophils—will be low. This type of blood count is typical of a stress response. The liver enzyme, ALT, will be high in most pets. Some pets will also have high ALP, LDH, AST, BUN, creatinine, glucose, phosphorus and bilirubin as they experience complications from hyperthyroidism.
Thyroid hormones, especially free T4, is elevated. T3 may also be elevated.