Cushing’s Disease Diagnosis: Not a Simple Matter

Is ACTH level useful for diagnosing Cushing’s disease in horses? The answer is yes, but it’s not as simple as looking at the result of one blood test.

ACTH, or adrenocorticotrophic hormone, is usually elevated in Cushing’s horses, but ACTH values rise and fall naturally in all horses according to time of day, season, and factors such as stress and pain. A study in England involved drawing blood from healthy older horses and those diagnosed with Cushing’s during 24-hour periods in March, June, September, and December.

ACTH levels were significantly higher in Cushing’s horses at all times of the day, and fluctuations were greater in Cushing’s horses than in normal horses. For all horses, levels were higher in September and December than in March and June. These results suggest that multiple tests might be better than a single test for an accurate diagnosis of Cushing’s disease.