Confirming the Diagnosis: Scans and Trends

Diagnosing tumor growth after an adrenalectomy has moved away from looking for a single “magic number” in a blood test. In the past, doctors might have waited for a very high ACTH level or visible skin changes to make a diagnosis ^[1]. Today, international medical consensus defines Corticotroph Tumor Progression (CTP-BADX) primarily through what is seen on a brain scan ^[2].

The Gold Standard: Thin-Section MRI

The most important tool for monitoring your health is a dedicated thin-section pituitary MRI ^[2]. Standard brain MRIs take “slices” that may be too thick to see small changes in a tiny gland like the pituitary. Thin-section scans take much more detailed images, allowing specialized radiologists to spot growth that is only a few millimeters in size ^[3].

According to the latest international guidelines, the diagnosis is typically made if a thin-section MRI shows ^[2]:

1. New Detection: A tumor appears where there wasn’t one visible before.
2. Radiological Progression: An existing tumor has clearly grown since your last scan.

Because prior surgeries, scanner differences, and measurement error can mimic small growth, images should be compared directly using a consistent protocol and interpreted by an experienced neuroradiologist/endocrinologist. A borderline change may need confirmation rather than immediate labeling as progression. Because many people (up to 68% in some cohorts) have no physical symptoms when this growth begins, these scheduled scans are the only way to catch progression early ^[4].

Tracking the ACTH Trajectory

Your doctor will also regularly measure your ACTH (adrenocorticotropic hormone) levels. High ACTH is an expected result of lost cortisol feedback, so one single high result is rarely enough for a diagnosis. Instead, doctors look at the trajectory—the direction and speed at which your numbers are changing ^[5].

• The Trend Matters: A rapid rise in ACTH over several months is often more concerning than a high number that stays stable ^[5].
• Early Warning Signs: In some research, an ACTH increase of more than 116 pg/mL within the first year after surgery was associated with a higher risk that a tumor might be starting to grow, though there is no generally applicable ACTH number that diagnoses progression ^[3].
• Timing is Key: To get an accurate trend, your blood should be drawn consistently according to your endocrinologist’s plan. Never delay or skip a daily or emergency steroid replacement dose on your own for a blood test, as this can cause an adrenal crisis. Record your steroid dose and the time you took it ^[6][7].

When the Lab Results Don’t Match

Sometimes, your blood test might show a very high ACTH level, but your MRI looks perfectly clear and you feel fine. In these cases, your doctor may investigate assay interference ^[8].

Medical labs use “assays” (chemical tests) to measure hormones. Uncommonly, other proteins in your blood can interfere with these tests, causing a “false high” reading ^[9]. Common causes of interference include:

• Heterophilic Antibodies: These are “sticky” antibodies in your blood that can accidentally bind to the test chemicals, making it look like you have more ACTH than you actually do ^[8].
• Platform Differences: Different labs use different brands of testing equipment. A sample that looks “high” on one machine (like the Siemens Immulite) might look “normal” on another (like a CIS Bio assay) ^[10][11].

If your numbers seem suspiciously high but your scans are stable, your endocrinologist and the clinical laboratory will investigate collaboratively. They can ask the lab to perform a “dilution study” or use “blocking reagents” to see if interference is skewing the results, but symptoms or MRI findings must never be disregarded while waiting for a different assay ^[8][12].