We have no evidence that the administration of prednisone, prednisolone or dexamethasone alters the serum concentrations of TLI or PLI in a clinically significant manner in clinically healthy animals. Thus the administration of glucocorticoids is highly unlikely to lead to either increases or decreases in serum TLI or PLI concentrations that would alter your clinical diagnosis.
If the animal has a disease causing malabsorption or increased release of pancreatic enzymes, and if the disease is glucocorticoid responsive, then abnormal values may become more normal or even normal when glucocorticoids are given. This may influence your interpretation, and you should consider the possibility that a high normal or only moderately increased TLI or PLI, in an animal with clinical signs of pancreatic disease that is receiving glucocorticoid therapy, may have been higher in the absence of the glucocorticoids.The serum vitamins, cobalamin and folate, usually do not show any change with prednisolone therapy alone,even if the diarrhea or weight loss improves. Typically you have to give vitamin supplements to make things normal, as we have described on our page regarding cobalamin therapy.
If you suspect that glucocorticoid administration has altered the clinical interpretation of TLI/PLI results, it may be worthwhile to draw a new sample after withdrawing the glucocorticoid therapy, assuming that the withdrawal of glucocorticoids is not contraindicated and consistent with the ongoing care of the patient. We would suggest waiting for at least 10 days after complete withdrawal of glucocorticoids before collecting a new serum sample.