Species: Canine and feline
Specimen: Serum
Container: Red top tube or gel separator tube
Collection protocol: Patients should be fasted UNLESS the test is for monitoring of treatment for hyperadrenocorticism. Animals on Trilostane therapy should receive their normal morning medication with a small amount of food and the ACTH stimulation test performed 4-6 hours after dosing.
DOGS:
- Collect a resting blood serum sample (red top tube) for a basal cortisol concentration and mark it “0 hour” in the morning.
- Allow tube to clot. If possible separate the serum from the red cells by centrifugation. If a plain tube has been used for the assay, centrifuge and transfer the serum from the collection tube into a plain (red top tube). Do not syringe into tube. Store at 4°C.
- Inject synthetic ACTH (Synacthen) 250 µg I/V (or l/M) regardless of bodyweight. More recently a protocol using a lower dose has been validated. This uses 5 µg/kg to a maximum of 250µg. One approach is to use the full dose for diagnosis and the lower dose for monitoring of therapy. When monitoring the same protocol needs to be used each time.
Care must be taken when aliquoting and storing the Synacthen once the vial is opened as it must remain sterile. Reconstituted Synacthen can be stored in the vial in the fridge for several weeks or be frozen for 6-12 months in a plastic syringe. A protocol is to reconstitute the vial with 5mL of saline which gives 50 µg/mL and store in 1 mL aliquots. One mL will then be used per 10 kg body weight.
If depot Synacthen is used, inject 250 µg I/M for dogs <15 kg and a higher dose of 500 µg/kg I/M for larger dogs.
- Collect a second serum sample one hour later and label it 1 hour and follow separation instructions as above.
- Place samples in the refrigerator until they can be transported to the laboratory.
CATS:
The method is as follows but the ACTH stimulation test is not recommended in cats for the diagnosis of hyperadrenocorticism as it is generally not sensitive enough.
- Collect a resting serum sample (red top tube) at zero hours and label it “0 hour”.
- Allow tube to clot. If possible separate the serum from the red cells by centrifugation. If a plain tube has been used for the assay, centrifuge and transfer the serum from the collection tube into a plain (red top tube). Do not syringe into tube. Store at 4°C.
- Inject synthetic ACTH (Synacthen) 125 µg I/V (or l/M). The same dose of 5 µg/kg which has been validated in dogs also appears adequate. There is no established protocol for the depot formulation in cats.
- Collect post ACTH blood sample at 1 hour, label as “1 hour”. Follow separation instructions as above
- Place samples in the refrigerator until they can be transported to the laboratory.
Special handling/shipping requirements: Samples should reach the laboratory within 24 hours of being collected.
General information about the disease:
See “Diagnosis and monitoring of hyperadrenocorticism – general guidelines” and “Diagnosis and monitoring of hypoadrenocorticism – general guidelines”.
General information about when this test is indicated:
Screening test for hyperadrenocorticism. Diagnosis of hypoadrenocorticism and iatrogenic hyperadrenocorticism. Monitoring the treatment of hyperadrenocorticism.
Comparison with other related tests:
See “Diagnosis and monitoring of hyperadrenocorticism – general guidelines” and “Diagnosis and monitoring of hypoadrenocorticism – general guidelines”.