Several research studies have shown that the endocrine (hormonal) disorders PPID and EMS are the most common cause of laminitis. For that reason, testing for PPID is often a vital part of a laminitis investigation. Increasing age is the major risk factor for PPID, with the disease affecting one in five horses over the age of 15 years. PPID is often slowly progressive, sometimes taking a period of months or years for obvious clinical signs to become apparent. Therefore, a negative test a few years previously certainly does not rule out a horse developing the disease in the future.
Measurement of the hormone ACTH is the most frequently used test for diagnosing PPID, and while it has high accuracy, it is very rare to have diagnostic test which is 100% perfect. For example, very early or mild cases of PPID may have only a small increase in their ACTH levels, returning a test result which is considered to be negative or borderline for PPID. The accuracy of ACTH testing for PPID is at its highest during the autumn months, so repeat testing at this time of year can be very useful for increasing the chances of detecting PPID. There are other diagnostic tests for PPID, and your vet would be able to recommend whether retesting your horse using a different test could be beneficial in this case.
If your horse has suffered from recurrent episodes of laminitis, or has shown any other clinical signs of PPID, repeating a blood test for PPID is definitely worth doing. Reaching a diagnosis for the underlying cause of the laminitis will allow your vet to provide the most appropriate advice regarding your horse’s management and treatment options where indicated.
Dr Jo Ireland, Veterinary epidemiologist at the Animal Health Trust