From the Guidelines
An ACTH test should ideally be done in the morning, around 8 am, to ensure accurate results and proper interpretation. This recommendation is based on the fact that ACTH levels follow a natural circadian rhythm, with highest levels occurring in the early morning and lowest levels in the evening 1. When diagnosing conditions such as hypophysitis, which can cause central adrenal insufficiency, it is crucial to conduct tests like the ACTH test at the optimal time to avoid misleading results. Some key points to consider when performing an ACTH test include:
- Testing should be done in the morning, preferably around 8 am, to coincide with the natural peak of ACTH levels 1.
- Patients should follow any specific preparation instructions from their healthcare provider, which may include fasting for a certain period before the test.
- The test involves a simple blood draw, usually from a vein in the arm.
- Stress can affect ACTH levels, so patients should try to remain calm before the test.
- If serial measurements are needed for diagnosis, they should be performed at the same time each day to ensure consistency. In the context of hypophysitis diagnosis, the ACTH test is just one part of the diagnostic workup, which also includes tests for thyroid function, gonadal hormones, and MRI of the sella 1.
From the Research
Timing of ACTH Test
- The ACTH test does not necessarily have to be done in the morning, but morning serum cortisol levels are often used as a screening test for adrenal insufficiency 2.
- Studies have shown that the correlation between morning serum cortisol and the peak cortisol response in the short ACTH test is high, suggesting that morning cortisol levels can be a useful predictor of adrenal insufficiency 2.
- However, other studies have investigated the nocturnal and early morning secretion of ACTH and cortisol, suggesting that the timing of the test may not be limited to the morning 3.
Diagnostic Cutoffs
- Recent studies have established new diagnostic cutoffs for adrenal insufficiency after cosyntropin stimulation using specific cortisol assays, which may be assay-specific and differ from historical cutoffs 4, 5.
- These studies suggest that the use of assay-specific cutoffs is essential for reducing misclassification and overtreatment in patients with suspected adrenal insufficiency 4, 5.
- The timing of the test may not be directly related to the diagnostic cutoffs, but rather to the protocol of the specific assay being used 6.
Protocol Variations
- Different protocols for the ACTH stimulation test have been studied, including the use of long-acting porcine sequence ACTH, which may offer an economical and accurate alternative to the short Synacthen test 6.
- The protocol for the test, including the timing and dosage, may vary depending on the specific assay and clinical context 2, 6.