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Laboratory evaluation of adrenal diseases

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Abstract

Each adrenal gland is composed of acortex and a medulla, which are functionally separate endocrine glands. The most common disorders affect the adrenal cortex and cause eitjer hyperadrenocorticism (HAC) or hypoadrenocorticism. This chapter considers canine hyperadrenocorticism, feline hyperadrenocorticism, canine hypoadrenocorticism, feline hypoadrenocorticism and other adrenal diseases. Readers will also find case examples included.

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Figures

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18.1 The regulation of cortisol release. ACTH = adrenocorticotropic hormone; CRH = corticotropin-releasing hormone.
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18.2 The regulation of aldosterone release. ACE = angiotensin converting enzyme; ACTH = adrenocorticotropic hormone.
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18.4 A summary of the investigation of canine hyperadrenocorticism (HAC). It is not necessary to perform all these investigations in every case. Text in blue refers to typical features of HAC; text in red refers to uncommon findings. ACTH = adrenocorticotropic hormone; ALP = alkaline phosphatase; ALT = alanine aminotransferase; 17-OHP = 17-hydroxyprogesterone; RBC = red blood cell.
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18.7 Interpretation of the ACTH stimulation test. Normal dogs show a 2–3-fold increase in cortisol concentrations but these remain <450 nmol/l. Most dogs with HAC have post-ACTH cortisol concentrations >600 nmol/l. False positive results occur with ‘stressful’ illnesses, such as unstable diabetes mellitus. The expected results in cases of iatrogenic HAC (iHAC) and hypoadrenocorticism (hAC) are also shown.
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18.9 Interpretation of the low-dose dexamethasone suppression test. Normal dogs show >50% suppression of cortisol concentrations at 3 hours with values <40 nmol/l at 8 hours. Dogs with HAC show little or no suppression at 8 hours. Cases with PD-HAC may show an initial suppression at 3 hours. The effects of iatrogenic HAC (iHAC) and hypoadrenocorticism (hAC) are also shown.
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18.10 Interpretation of 17-hydroxyprogesterone (17-OHP) assay. Normal dogs show a 2–3-fold increase in 17-OHP concentrations but these remain <10 nmol/l. Most dogs with typical or atypical HAC have post-ACTH 17-OHP concentrations >8 nmol/l. False positive results may occur with ‘stressful’ illnesses, such as unstable diabetes mellitus, neoplasia and liver disease. False negatives can also occur but are uncommon.
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18.11 Interpretation of ACTH stimulation tests in the monitoring of trilostane treatment of canine hyperadrenocorticism.
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18.12 Suggested interpretation of pre- and 2–3 hour post-pill cortisol in the monitoring of trilostane treatment of canine hyperadrenocorticism (HAC). (a) The clinically well controlled patient. (b) The patient appears clinically well but there are signs that HAC is not controlled. (c) The clinically unwell patient.
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18.13 Hyperfragile skin in a cat with hyperadrenocorticism
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18.15 A summary of the investigation of canine hypoadrenocorticism. It is not necessary to perform all these investigations in every case. Text in blue refers to typical features of hypoadrenocorticism; text in red refers to uncommon findings. ACTH = adrenocorticotropic hormone; GI = gastrointestinal; RBC = red blood cell; WBC = white blood cell.
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18.20 A 13-year-old female neutered Collie cross showing altered coat colour over the trunk and flank alopecia.
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18.21 A 3-year-old male neutered Standard Poodle in a semicollapsed state. Intravenous fluid therapy has been initiated.
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