I have secondary adrenal deficiency due to pituitary injury. I've been taking 5mg prednisone in the morning and 5mg Cortef at noon. Normally I have cortisol levels done in the AM without any meds; but last time, I took my labs after taking prednisone.
I took 5mg prednisone at 6 am and my 9am serum cortisol was 1.7 ug/dL. This is much lower than my usual a.m. cortisol (5-7ug/dL).
I did some research and an endocrinology textbook (thank you Google books!) stated "Patients taking prednisone may have falsely increased cortisol levels because prednisone is converted to prednisolone after ingestion, and prednisolone has a 41% cross-reactivity with cortisol. " Is that true for a 5mg dose or just for huge suppressive doses (e.g., 50 mg)? It seems very strange for me to have such a low serum cortisol reading after taking the prednisone.
Two immediate family members have a rare form of hypertension - apparent mineralocorticoid excess. Any salt gives them dangerous hypertension, but taking cortef will lower their blood pressure. It's due to an enzyme defect. I wonder if I have a version of it. Four out of five immediate family members use cortef, three of us are also hypothyroid. So we have some strange endocrine patterns.