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P. L. Padfield, J. R. Seckl, B. R. Walker, H. K. Gleeson, Letter re: HPA Axis Testing after Pituitary Surgery, The Journal of Clinical Endocrinology & Metabolism, Volume 90, Issue 8, 1 August 2005, Pages 4981–4982, https://doi.org/10.1210/jc.2004-2470
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To the editor:
Courtney et al. (1) describe testing of the hypothalamic-pituitary-adrenal (HPA) axis 4–6 wk after pituitary surgery and report discrepancies between the plasma cortisol response to a standard (250 μg) short synacthen test (SST) and to insulin-induced hypoglycemia (ITT) in 11 of 41 patients. However, there were only three patients (I, J, and K in Table 1) in whom the 30-min cortisol result during the SST was discrepant from the ITT. To argue that patients would have been mismanaged if decisions had been based on their SST result is critically dependent on the cut-off used to define a “normal” cortisol. For the SST, their figure of 500 nmol/liter (18.1 μg/dl) was based on studies in 16 normal volunteers, whereas for the ITT they used the “historical” cut-off at 550 nmol/liter (19.9 μg/dl). Our earlier survey of UK endocrinologists (2) suggested that 550 was an archaic figure based upon very different assays for cortisol than are used currently. Our cut-off for the standard SST is a 30-min cortisol of 460 nmol/liter (16.7 μg/dl), extrapolated from previous normative data and corrected for changes in assay methodology. Thus, it is our contention that these three patients probably had normal HPA axes and repeat testing might have been a better management plan for J and K than lifelong glucocorticoid therapy.
