Confirming the Diagnosis: Scans and Blood Tests

The journey from a “flagged” newborn screen to a definitive diagnosis of athyreosis involves several specialized steps. It is important to distinguish between the screening, which is a broad “safety net” designed to catch potential issues (usually performed at 24-48 hours of life), and diagnostic testing, which confirms exactly what is happening in your baby’s body ^[1][2].

The Role of Imaging: Seeing the Invisible

To confirm that the thyroid gland is truly missing, doctors use two different types of imaging. Using both together is considered the best practice because they “see” the body in different ways.

• Thyroid Scintigraphy (The Functional Scan): In this test, a tiny, safe amount of a “tracer” (usually Technetium-99m) is given to the baby. A special camera then looks to see if any thyroid tissue “grabs” that tracer. If no tracer is absorbed anywhere in the body, it suggests athyreosis ^[3][4].
• Thyroid Ultrasound (The Structural Scan): This uses sound waves to create a picture of the neck. While scintigraphy shows if tissue is working, the ultrasound looks to see if any tissue is physically present. Sometimes, a baby might have a very small, non-working gland that the scan misses but the ultrasound finds. Confirming the physical absence with an ultrasound helps doctors ensure the diagnosis is accurate ^[4][5].

Using both tests prevents a “misdiagnosis.” For example, a baby with a misplaced (ectopic) gland or a temporary thyroid issue might show no uptake on a scan but still have tissue visible on an ultrasound ^[4][6].

Biochemical Clues

Beyond pictures, your baby’s blood work provides clues about the severity of the condition.

• Hormone Levels: Infants with athyreosis typically have the most significant “signals” of thyroid deficiency. This usually means a very high TSH (often above 100 mU/L) and very low T4 or fT4 levels ^[7][8].
• Thyroglobulin (Tg): This is a protein made only by thyroid cells. In true athyreosis, thyroglobulin levels are usually extremely low or undetectable because there are no cells to produce it ^[9].

Your Diagnostic Completeness Checklist

To ensure your baby has had a thorough evaluation, you can check for the following:

1. [ ] Confirmatory Blood Work: High TSH and low T4/fT4 measured from a vein (not just the heel prick) ^[1].
2. [ ] Thyroglobulin (Tg) Level: To check for the presence of any thyroid cells ^[9].
3. [ ] Thyroid Scintigraphy: To look for active thyroid tissue anywhere in the body ^[3].
4. [ ] Thyroid Ultrasound: To confirm the physical absence of the gland in the neck ^[4].

Additional Tests Your Doctor May Consider

• Bone Age X-ray: Because thyroid hormone is needed for bone growth even before birth, doctors may take an X-ray of the baby’s knee. In babies with athyreosis, the knee bone development may be delayed ^[7]. While this helps determine the severity of prenatal hypothyroidism, it is not universally mandated by all clinical guidelines to confirm the diagnosis, and it does not change the immediate medication protocol. If your doctor skipped this test, there is no need to panic.