INS and Hyperglycemia: However, the data at hand can only indicate that absolute insulin deficiency per se is not the cause of the hyperglycemia and suggest other possibilities that merit investigation, namely (1) abnormal tissues with a high threshold for the action of insulin; (2) an abnormal insulin that acts poorly with respect to hormonal activity in vivo but reacts well immunologically in vitro; (3) an abnormally rapid inactivation of hormonally active sites ... but not of immunologically active sites on the insulin molecules; and (4) the presence of insulin antagonists.