Is a baseline cortisol at 0 minutes necessary to do as part of an ACTH stimulation test when performing the test in late morning or in the afternoon?

The peak cortisol value after 250 μg cosyntropin changes a little based on when it is done. We see a bigger delta cortisol if it is done in the afternoon. One may omit the baseline cortisol to cut back on costs or if there is a time constraint (avoiding going to the lab and then coming back for an i...