Principles of interpreting endocrine test results

Peter A. Graham

doi:10.22233/9781910443866.4

British Small Animal Veterinary Association , 22 (2023); https://doi.org/10.22233/9781910443866.4

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fPrinciples of interpreting endocrine test results

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Author: Peter A. Graham
From: BSAVA Manual of Canine and Feline Endocrinology
Item: Chapter 4, pp 22 - 28
DOI: 10.22233/9781910443866.4
Copyright: © 2023 British Small Animal Veterinary Association
Publication Date: August 2023

Abstract

The interpretation of endocrine laboratory test results can be complicated by the interrelatedness of endocrine systems with other physiological systems and by environmental factors. However, with an understanding of endocrine physiology, the impact of non-endocrine factors and the limitations of diagnostic tests, it is possible to confidently confirm the presence or absence of endocrine disease. This chapter covers diagnostic sensitivity and specificity, the need for caution when interpreting results near reference limits and cut-off values, and the effects of endocrine and non-endocrine factors.

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4.4

Effect of pre-test probability (prevalence) on positive predictive value (PPV) and negative predictive value (NPV) and diagnostic accuracy using the low-dose dexamethasone suppression test for diagnosing canine hypercortisolism. The NPV and PPV are calculated from the 95% sensitivity and 71% specificity reported by Van Liew et al. (1997 ). At low prevalence, PPV is low (5% prevalence is associated with 15% PPV). To have 90% confidence in a positive test result being true requires a pre-test probability of 75%, and a PPV >95% requires a pre-test probability of 85% (purple arrows). However, at such high pre-test probabilities, the confidence in negative results falls. Confidence in a negative test result is >90% at all pre-test probabilities below 60%. © 2023 British Small Animal Veterinary Association

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4.4 Effect of pre-test probability (prevalence) on positive predictive value (PPV) and negative predictive value (NPV) and diagnostic accuracy using the low-dose dexamethasone suppression test for diagnosing canine hypercortisolism. The NPV and PPV are calculated from the 95% sensitivity and 71% specificity reported by Van Liew et al. (1997 ). At low prevalence, PPV is low (5% prevalence is associated with 15% PPV). To have 90% confidence in a positive test result being true requires a pre-test probability of 75%, and a PPV >95% requires a pre-test probability of 85% (purple arrows). However, at such high pre-test probabilities, the confidence in negative results falls. Confidence in a negative test result is >90% at all pre-test probabilities below 60%.

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[ref-ch04_1] Bergman D , Larsson A , Hansson-Hamlin H , Åhlén E and Holst BS (2019a) Characterization of canine anti-mouse antibodies highlights that multiple strategies are needed to combat immunoassay interference. Scientific Reports 9 , 14521 [Crossref]
[Google Scholar]

[ref-ch04_2] Bergman D , Larsson A , Hansson-Hamlin H and Holst BS (2019b) Investigation of interference from canine anti-mouse antibodies in hormone immunoassays. Veterinary Clinical Pathology 48 Suppl 1, 59–69 [Crossref]
[Google Scholar]

[ref-ch04_3] Davison LJ , Herrtage ME and Catchpole B (2011) Autoantibodies to recombinant canine proinsulin in canine diabetic patients. Research in Veterinary Science 91 , 58–63 [Crossref]
[Google Scholar]

[ref-ch04_4] Dixon RM and Mooney CT (1999) Evaluation of serum free thyroxine and thyrotropin concentrations in the diagnosis of canine hypothyroidism. Journal of Small Animal Practice 40 , 72–78 [Crossref]
[Google Scholar]

[ref-ch04_5] Fraser CG and Sandberg S (2018) Biological variation. In: Tietz Textbook of Clinical Chemistry and Molecular Diagnostics , 6th edn, ed. N Rifai , AR Horvath and C Wittwer , pp. 157–169. Elsevier, St. Louis
[Google Scholar]

[ref-ch04_6] Gold AJ , Langlois DK and Refsal KR (2016) Evaluation of basal serum or plasma cortisol concentrations for the diagnosis of hypoadrenocorticism in dogs. Journal of Veterinary Internal Medicine 30 , 1798–1805 [Crossref]
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[ref-ch04_7] Hegstad-Davies RL , Torres SM , Sharkey LC et al. (2015) Breed-specific reference intervals for assessing thyroid function in seven dog breeds. Journal of Veterinary Diagnostic Investigation 27 , 716–727 [Crossref]
[Google Scholar]

[ref-ch04_8] Iversen L , Jensen AL , Høier R and Aaes H (1999) Biological variation of canine serum thyrotropin (TSH) concentration. Veterinary Clinical Pathology 28 , 16–19 [Crossref]
[Google Scholar]

[ref-ch04_9] Jensen AL and Høier R (1996) Evaluation of thyroid function in dogs by hormone analysis: effects of data on biological variation. Veterinary Clinical Pathology 25 , 130–134 [Crossref]
[Google Scholar]

[ref-ch04_10] Jensen AL , Høier R and Pedersen HD (1993) Evaluation of an enzyme linked immunosorbent assay for the determination of free thyroxine in canine plasma samples assisted by data on biological variation. Zentralblatt für Veterinārmedizin A 40 , 539–545 [Crossref]
[Google Scholar]

[ref-ch04_11] Prieto JM , Carney PC , Miller ML et al. (2020) Short-term biological variation of serum thyroid hormones concentrations in clinically healthy cats. Domestic Animal Endocrinology 71 , 106389 [Crossref]
[Google Scholar]

[ref-ch04_12] Van Liew CH , Greco DS and Salman MD (1997) Comparison of results of adrenocorticotropic hormone stimulation and low-dose dexamethasone suppression tests with necropsy findings in dogs: 81 cases (1985–1995). Journal of the American Veterinary Medicial Association 211 , 322–325
[Google Scholar]

[ref-ch04_13] Zeugswetter F , Bydzovsky N , Kampner D and Schwendenwein I (2010) Tailored reference limits for urine corticoid:creatinine ratio in dogs to answer distinct clinical questions. Veterinary Record 167 , 997–1001 [Crossref]
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