Biochemical indication of remission
Early morning serum cortisol measured between 8 and 10 a.m. is the most commonly utilized measure of immediate remission following surgery. Cortisol secretion normally follows a diurnal pattern with highest levels between 7–9 a.m. that decline to lowest levels around 10–11 p.m. [9]. In patients with CD, the circadian rhythm is aberrant and cortisol levels remain consistently elevated [9, 10]. The goals of pituitary surgery are to extract the ACTH-secreting adenoma and subsequently reduce cortisol levels, leading to improvements in the signs and symptoms of CD.
Surgical success is confirmed by subnormal levels of early morning serum cortisol measured within a few days of surgery. Typically, early morning serum cortisol levels of either <2 µg/dL (~50 nmol/L) or <5 µg/dL within a few days after surgery are considered to be indicative of remission [3]. However, reported results are mixed and difficult to interpret since some studies measure basal serum cortisol levels while others use serum cortisol following dexamethasone suppression, or some combination of these measures [5, 11–13]. While clinical practice guidelines provide recommendations for testing in the context of initial diagnosis of CD [10], there is no expert consensus with regard to post-operative testing for surgical success.
The timing of biochemical measurements differs among treatment centers and can vary considerably within the same center. Intervals between surgery and biochemical measurement range from 1 to 2 days [14, 15], up to several weeks [16, 17], and even months [14]. As a result, the definition of post-surgical remission is unclear.