Endocrine Abstracts

Background: The insulin stress test (IST) is accepted as the gold standard investigation of the hypothalamio-pituitary–adrenal axis (HPA). The short synacthen test (SST) has been advocated as an alternative to the IST. Fatigue can be a common presenting symptom of patients suffering from abnormalities in the HPA axis.

Methods: We audited the results of ISTs following failed SSTs for the assessment of patients who present with symptoms of fatigue. We included all patients from July 2007 to July 2009 who failed a short synacthen test (defined as a cortisol of <540 nmol/l after 30 min) who subsequently had an IST. Data was obtained through the central laboratory database serving the Trust and review of patient notes and clinical letters.

Results: There were a total of 16 patients who were included in this analysis. All patients presented with fatigue with no abnormal physical signs and had normal biochemistry and full blood count. Of the 16 patients (14 F, 2 M mean age 44.7 years), 12 (75%) patients passed the IST (peak cortisol >500 nmol/l) and four (25%) failed to achieve this value. None of the 30 min cortisol results from the SST were below 400 nmol/l. Of the four patients who failed the IST, three patients had autoimmune disease (two with hypo/hyperthyroidism, one with pernicious anaemia). Of the 12 patients who passed the IST, only 1 patient had a previously established autoimmune disease.

Conclusion: For patients with fatigue and an established autoimmune disease the IST is most likely to show an abnormality of the HPA axis following a suboptimal SST.