Determination of Method-specific Normal Cortisol and Adrenal Hormone Responses to the Short Synacthen Test
Condition: Healthy; Adrenal Insufficiency; Hypopituitarism
MeSH terms: Hypopituitarism; Adrenal Insufficiency
Study type: Interventional
Phase: Phase 4

Summary: 
      Objectives:

      To establish valid serum total cortisol and salivary cut-offs for use with the short
      Synacthen test in patients with normal CBG concentrations.

      To investigate, using current assays, the effect of assay differences on the serum total
      cortisol cut-off.

      To explore the performance of these cut-offs in groups of patients with suspected adrenal
      insufficiency and high and low serum CBG concentration.

      Methodology: An ACTH test (250 micrograms iv ACTH1-24) will be undertaken in healthy
      volunteers, women taking an oestrogen-containing oral contraceptive pill (OCP), patients with
      adrenal insufficiency and patients with low serum albumin. Serum cortisol in the samples
      collected from healthy volunteers will be measured using GC-MS, Advia Centaur (Siemens),
      Architect (Abbott), Modular Analytics E170 (Roche), Immulite 2000 (Siemens) and Access
      (Beckman) automated immunoassays. The estimated lower reference limit for the 30 min cortisol
      response to ACTH, defined as the 2.5th percentile of log-transformed concentrations, will be
      determined in this healthy population and used as a cut-off in the patient groups studied.
    

Detailed description: 
      Synacthen® is a synthetic analogue of ACTH which has been used since the 1960s to assess
      adrenal sufficiency. It is now well established as a first line test to investigate diseases
      of the hypothalamo-pituitary-adrenal axis and to assess adrenal function in patients on
      long-term corticosteroid therapy. Briefly, cortisol is measured before and after injection of
      250 micrograms of Synacthen®. In a normal individual serum cortisol will rise to
      concentrations greater than an arbitrary value (typically 550 nmol/l) 30 minutes after
      administration of Synacthen®.

      In 2004 the All Wales Clinical Biochemistry Audit group surveyed protocols for performing and
      interpreting short Synacthen® tests. This identified wide differences in practice within
      Wales. As a result standards were drawn up for performance of the test. It was noted that
      there was considerable variability or bias between cortisol immunoassays and that the
      cortisol cut-off chosen for interpretation of the short Synacthen® test should be method
      dependent.

      Clark et al., in 1998 reported cortisol cut-offs following Synacthen® using 4 well
      established commercially available cortisol immunoassays. This study demonstrated
      considerable differences between the cortisol immunoassays used in clinical laboratories at
      the time. It was also apparent that there were differences in gender-related responses to
      Synacthen® although there was no dependence on age. In the 8 years since publication of this
      study there have been advances in formulation of cortisol immunoassays as well as the
      instrumentation used to perform analyses. At the University Hospital of Wales cortisol is
      currently assayed using the Bayer Centaur automated immunoassay analyser. This assay was not
      available at the time of the study by Clark et al.,. The investigators' current short
      Synacthen® test cut-offs therefore rely on historical reference ranges which have become
      outdated. A re-evaluation of the cortisol cut-off is required to ensure that patients are not
      incorrectly classified.

      It has been long been recognised that oestrogens (including ethinyloestradiol prescribed in
      combined oral contraceptive pills) increase total (but not free) serum cortisol levels. The
      degree of increase is related to the dose used and is thought to be due to an elevation in
      cortisol binding globulin (CBG). However, no comparisons of total serum cortisol in response
      to Synacthen® have been performed between women taking oestrogens and those who are not.
      Knowledge of the salivary cortisol response may also be useful in patients with decreased
      serum CBG concentrations e.g. severe nephrotic syndrome in whom the serum cortisol response
      may be misleading. The investigators therefore plan to measure salivary cortisol as part of
      the investigators' study protocol to assess the response of free cortisol.

      17 Hydroxyprogesterone (17OHP) is an intermediate in the biosynthesis of cortisol. Deficiency
      of 21-hydroxylase enzyme activity leads to an increased concentration of 17OHP in the
      peripheral circulation. The short Synacthen® test can be used to assist in diagnosis of mild
      cases of congenital adrenal hyperplasia. Current reference ranges are taken from the
      literature.
    

Intervention name(s): Synacthen (Tetracosactrin)
Intervention type(s): Drug
Intervention description(s): IV injection of 250 micrograms of Synacthen in 1ml
Other intervention name(s): Synacthen
Intervention MeSH terms: Cosyntropin
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Diagnostic
Keywords: Volunteer; Hypoadrenalism; Hypopituitarism; Healthy volunteers