[Study on the reproducibility of ACTH concentrations in plasma of horses with and without equine Cushing syndrome].

This research paper investigates the consistency of plasma ACTH measurements in horses suffering from pituitary pars intermedia dysfunction (PPID), also known as Cushing’s disease, across different laboratories and within the same laboratories. The study, which involved testing blood samples from both ailing and healthy horses, found significant discrepancies in the recorded ACTH levels, demonstrating that the testing methods and conditions could highly influence the result.

Objective of the Study

• The aim of this study was to examine whether ACTH (adrenocorticotrophic hormone) measurements vary across different laboratories and within the same facility. ACTH is a crucial hormone in diagnosing PPID or equine Cushing’s disease in horses.
• An additional goal was to determine whether the use of different sampling protocols and conditions such as time of centrifugation and use of proteinase inhibitors could affect the consistency of ACTH readings.

Methods Used in the Study

• The study involved sampling the plasma of ten horses diagnosed with PPID and four healthy horses. Each sample was split into two, labelled differently, and sent to all four participating laboratories.
• Samples were collected in the morning and sent out for analysis according to each lab’s standard process.
• The blood was centrifuged either immediately after being drawn or after one hour to ascertain the impact this might have on ACTH levels.
• The influence of proteinase inhibitors (aprotinine) on ACTH values was also assessed.

Results of the Study

• The results indicated a considerable variation in the ACTH readings, not only across the different labs but also within the same lab where the blood of a single horse showed a standard deviation ranging from +/- 6 to +/- 27 pg/ml within a lab.
• Between laboratories, the standard deviation ranged typically at +/- 26.4 pg/ml, emphasizing the considerable discrepancies in the results.
• There was notable variation observed in individual horses’ ACTH levels, with one 20-year-old gelding showing a lowest ACTH value of 60.9 pg/ml and a highest of 108 pg/ml.
• Immediate centrifugation of blood samples showed higher ACTH values by an average of 11.6 pg/ml, suggesting that the time of centrifugation does influence the results.
• However, the study found that the use of proteinase inhibitors had no significant effect on ACTH values.

Challenges and Implications

• This study highlights the inherent issues present in current ACTH testing and its variability. The differences may be due to different laboratory standards or testing conditions, questioning the reproducibility and reliability of such tests.
• These findings emphasize the need for standardized processes within and across laboratories to ensure accurate measurements, particularly for a crucial hormone like ACTH in the diagnosis of PPID.