The simplest and most common test for PPID is the basal or resting ACTH test. To perform this test your vet will take a blood sample from your horse and send it to a laboratory. The results of the test can be compared to reference ranges (which will change with the seasons) to confirm the presence or absence of PPID.
However the basal ACTH test is not perfect and will not always pick up all cases of PPID. If your horse tests negative for PPID but continues to show clinical signs of the disease it may be worth re-testing at a later date.
Sometimes the results of this test are not clear cut. The test results can fall into a ‘grey zone’ between a clearly positive and a clearly negative result. If this happens to your horse your vet may recommend re-testing after 3-6 months, or performing an alternative test called a TRH stimulation test.
The measurement of serum insulin and glucose is often recommended in PPID cases and acts as an indicator of both laminitis risk as well as the likely outlook for the patient.1