Comparison of two methods for measurement of equine adrenocorticotropin

Banse, Heidi E.; Schultz, Nichol; McCue, Molly E.; Geor, R. J.; McFarlane, Dianne

doi:10.1177/1040638717752216

Cited by 13 publications

(10 citation statements)

References 19 publications

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“…The assay used to measure ACTH concentration is important for the clinical interpretation of the results. Poor agreement between equine [ACTH] values measured using CL methods and a commercial radioimmunoassay has been reported previously [11]. The findings of this study agree with those of Irvine et al [3] and Knowles et al [7], demonstrating that the [ACTH] is also significantly lower when measured using IF compared to CL methods in concurrently run samples obtained from horses or ponies at baseline or ponies post TRH stimulation test.…”

Section: Discussionsupporting

confidence: 81%

Comparison of immunofluorescence and chemiluminescence assays for measuring ACTH in equine plasma

McGilvray

Knowles

Harris³

et al. 2020

Equine Veterinary Journal

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Background:The chemiluminescence (CL) and immunofluorescence (IF) assays yield different results for basal adrenocorticotropin hormone concentrations [ACTH] in pony plasma. It is unclear whether this difference also occurs in basal samples from horses or samples from ponies following thyrotropin-releasing hormone (TRH) stimulation.Objectives: To compare the results of [ACTH] analysis by CL and IF methods in basal samples from horses and pony samples following TRH stimulation. Study design: Method comparison.Methods: Plasma [ACTH] was measured concurrently using CL and IF methods in 12 ponies (basal and post TRH stimulation) in November and basal samples from horses (n = 45; November and May).Results: CL and IF methods yielded different results (P<0.01). The median difference (CL -IF) (95%CI) for ponies was 5.9 (0.1-7.5)pg/ml at baseline and 227.9 (61-1001)pg/ml post TRH; and horses 1.9 (1.1-5.4)pg/ml in November and 9.4 (8.2-11.5)pg/ml in May, at baseline. Correlation was good in ponies at baseline (R=0.80, p=0.003) but not post TRH, and good in horses in November and May (R=0.68 and 0.71, p<0.001). Bland-Altman analysis demonstrated moderate bias and wide 95% limits of agreement (95%LOA) in ponies at baseline (bias 5.5pg/ml; 95%LOA -9.9-20.9pg/ml) and horses in May (bias 10.6pg/ml; 95%LOA -9-30.3pg/ml) and very large bias and wide 95%LOA in ponies post TRH (bias 477pg/ml; 95%LOA -633-1587pg/ml). Using CL cut-offs of >29pg/ml and >110pg/ml, agreement was moderate (ƙ=0.67) and very good (ƙ=0.82) for binary classification of PPID in ponies at baseline and post TRH; and good (ƙ=0.73) for horses in November, but poor (ƙ=0.40) in May. Main limitations:Limited numbers of horses with [ACTH] above threshold values. Conclusions:The assays yielded different absolute values, particularly in post TRH samples from ponies, suggesting TRH stimulates secretion of cross-reacting peptides other than ACTH. Agreement for binary classification for PPID was moderate to good, except in basal samples from horses in May.

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Section: Discussionsupporting

confidence: 81%

Comparison of immunofluorescence and chemiluminescence assays for measuring ACTH in equine plasma

McGilvray

Knowles

Harris³

et al. 2020

Equine Veterinary Journal

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“…In our study, however, the magnitude of the bias and the variations were greater than previously reported. A possible explanation for this discrepancy is the difference in assays used between studies with the radio‐immunoassay, commonly used in previous studies, reporting lower immunoreactive ACTH concentrations than chemiluminescent assays 26 . Another explanation could be the physiological effect of season on our results; however, one would expect an increase in immunoreactive plasma ACTH concentrations between week 1 and week 2 rather than the decrease observed in our study.…”

Section: Discussioncontrasting

confidence: 65%

“…A possible explanation for this discrepancy is the difference in assays used between studies with the radio‐immunoassay, commonly used in previous studies, reporting lower immunoreactive ACTH concentrations than chemiluminescent assays. 26 Another explanation could be the physiological effect of season on our results; however, one would expect an increase in immunoreactive plasma ACTH concentrations between week 1 and week 2 rather than the decrease observed in our study. Finally, in absence of changes in diet, a likely explanation is the low number of horses enrolled in our study and the higher number of horses with PPID; however, this number is similar to previous reports.…”

Section: Discussionmentioning

confidence: 53%

Repeatability of a thyrotropin‐releasing hormone stimulation test for diagnosis of pituitary pars intermedia dysfunction in mature horses

Kam

McKenzie

Coyle

et al. 2021

Veterinary Internal Medicne

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Background Pituitary pars intermedia dysfunction (PPID) is a common endocrinopathy of horses diagnosed with a thyrotropin‐releasing hormone (TRH) stimulation test. Hypothesis/Objectives Describe the repeatability of TRH stimulation in horses with and without PPID in winter and autumn. Animals Twenty adult horses; 6 controls and 6 with PPID tested in autumn, 8 controls and 6 with PPID tested in winter with 3 controls and 3 with PPID tested in both seasons. Methods Thyrotropin‐releasing hormone stimulation was performed on 2 consecutive occasions, 1 week before and 1 week after the winter solstice and the autumn equinox. Blood was collected before and 30 minutes after IV injection of 1 mg of TRH. ACTH concentration was determined by a chemiluminescent assay. Repeatability and test‐retest reliability were assessed by repeated measures analysis of variance, intraclass correlation coefficient and within‐horse coefficients of variation (CV). Bland‐Altman plots were generated to visualize agreement between repetitions. Results In winter, no week effect was detected on the results of the TRH simulation and the test had an excellent test‐retest reliability. In autumn, after‐TRH ACTH concentrations were significantly lower on week 2 (P = .02) and the test only had a good test‐retest reliability. There were significantly larger within‐horse CV during autumn (P = .04) and after TRH stimulation (P = .04). There were 2 misclassifications in winter and 4 in autumn. Conclusions and Clinical Importance The TRH stimulation test was repeatable when performed 2 weeks apart in winter; however, in autumn, more variability in after‐TRH ACTH concentrations resulted in decreased repeatability.

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“…Durham, unpublished data). It is also worthy of note that other methodologies might not generate values that vary in any predictably linear fashion meaning that extrapolation may prove impossible 31,32 …”

Section: Discussionmentioning

confidence: 99%

Clinically and temporally specific diagnostic thresholds for plasma ACTH in the horse

Durham¹,

Clarke

Potier³

et al. 2020

Equine Veterinary Journal

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Background Pituitary pars intermedia dysfunction (PPID) is commonly investigated using plasma ACTH concentrations but problems exist with currently available diagnostic thresholds. Objectives To derive temporally specific diagnostic thresholds for equine plasma ACTH concentration to be used alongside clinical judgement in each individual week of the year and appropriate for the degree of clinical suspicion in any given case. Furthermore, to apply these thresholds to compare the prevalence of high and low ACTH in two subgroups of animals with high and low clinical suspicion of PPID. Study design A retrospective population study examining a large laboratory database of equine plasma ACTH concentrations using an indirect approach to calculate diagnostic thresholds. Methods Logs of plasma ACTH concentrations from 75 892 individual horses were examined using robust L2 estimation of mixtures of two normal distributions in categories of each week and month of the year. Thresholds dividing the two populations of high‐ACTH and low‐ACTH horses were then established at different levels of sensitivity and specificity and compared with clinical subgroups of horses divided based on reported clinical signs, as having high (n = 4036) or low (n = 3022) clinical suspicion of PPID. Results For most of the year there were small interweek differences in diagnostic thresholds. However, from mid‐June to early‐December diagnostic thresholds showed greater interweek variability, reaching a maximum in late September and early October. Grouping of high‐ and low‐ACTH compared favourably with grouping based on clinical signs. Main limitations Given the multiple sources of diagnostic samples, pre‐analytical data could not be fully verified. Conclusions Diagnostic thresholds for equine plasma ACTH vary through the year. It is especially important to consider the temporally specific threshold between June and December. Different clinical thresholds can be used depending on the case circumstances and whether a false‐positive or false‐negative diagnosis is deemed least desirable.

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Comparison of two methods for measurement of equine adrenocorticotropin

Cited by 13 publications

References 19 publications

Comparison of immunofluorescence and chemiluminescence assays for measuring ACTH in equine plasma

Comparison of immunofluorescence and chemiluminescence assays for measuring ACTH in equine plasma

Repeatability of a thyrotropin‐releasing hormone stimulation test for diagnosis of pituitary pars intermedia dysfunction in mature horses

Clinically and temporally specific diagnostic thresholds for plasma ACTH in the horse

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