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PubMed This is a summary of 15 peer-reviewed journal articles Updated
Pediatric Endocrinology

Diagnostic Workup and Understanding Scans

At a Glance

An abnormal newborn thyroid screen requires a diagnostic venous blood test to confirm congenital hypothyroidism. If confirmed, doctors use safe imaging like ultrasounds or scintigraphy to locate the thyroid gland and determine if the condition is permanent or temporary.

If your baby’s newborn screening indicated a potential issue with their thyroid, the next step is a diagnostic workup. This process moves from a broad “screening” to specific “diagnostic” tests designed to confirm the diagnosis and identify the exact cause [1].

From Screening to Diagnosis

The journey usually begins with a newborn screening (NBS), often called the “heel prick” test. This is a highly sensitive screen designed to catch as many cases as possible [2].

  • TSH Cutoffs: Screening laboratories use a specific threshold or cutoff for Thyroid Stimulating Hormone (TSH) [3]. If a baby’s TSH is higher than this number, it flags the need for further testing [4].
  • False Positives: Because the screening is designed to be “sensitive” (to avoid missing any babies), it sometimes results in false positives—where the screen is abnormal, but the baby’s thyroid is actually functioning normally [2]. Factors like prematurity, the timing of the test, or even the temperature of the room where the blood spot was stored can sometimes cause these results [5][6].
  • Definitive Blood Tests: To confirm the diagnosis, doctors perform a venous blood test (taking blood from a vein) to measure serum TSH and Free T4 (FT4) [1]. A diagnosis of hypothyroidism is typically confirmed if the TSH is high and the FT4 is low [7].

Understanding Imaging: Scans and Ultrasounds

Once the diagnosis is confirmed, your doctor may order imaging to see what the thyroid looks like. This helps determine the underlying cause [8].

  • Thyroid Ultrasound: This uses sound waves to create a picture of the neck [8]. It is excellent for seeing if a thyroid gland is present in the normal location [9]. However, it may sometimes miss a very small gland that is in the “wrong” place [8].
  • Thyroid Scintigraphy (Radionuclide Scan): This is a specialized scan where a tiny, incredibly safe amount of a marker is injected into a vein [9]. The radiation exposure is extremely low and rigorously tested for infant safety. The scan shows where the thyroid tissue is actually “working” [10]. It is the “gold standard” for identifying ectopy (a gland in the wrong place) or agenesis (a missing gland) [9].
  • Why it Matters: If the scan shows the gland is missing or in the wrong place (dysgenesis), the condition is almost always permanent [11]. If the gland is in the right place but not working (dyshormonogenesis), it might be due to a genetic factor [9].

Permanent vs. Transient Hypothyroidism

Not every baby diagnosed with CH will need medication for their entire life. Doctors distinguish between two types:

  1. Permanent CH: This requires lifelong treatment with thyroid hormone [12]. It is most common when the gland is missing, small, or in the wrong place [11].
  2. Transient CH: This is a temporary condition where the thyroid eventually starts working on its own [13]. It is more common in babies who were born prematurely or in cases where certain antibodies from the mother temporarily affected the baby’s thyroid [6][14].

Because it can be hard to tell the difference at birth, most babies are treated immediately to protect their brain development [13]. Doctors typically wait until the child is about 3 years old to perform a “trial” off the medication to see if the thyroid can now function on its own [15].

Common questions in this guide

What is the difference between the newborn screening and the diagnostic blood test?
The newborn screening is a sensitive heel prick test designed to flag potential issues early. To confirm the diagnosis, doctors perform a venous blood test that measures exact TSH and Free T4 levels in your baby's blood.
Why might a newborn thyroid screening have a false positive result?
False positives can occur if a baby is born prematurely or based on the exact timing of the heel prick test. Sometimes, environmental factors like the temperature of the room where the blood spot was stored can also impact the results.
Why does my baby need a thyroid ultrasound or scintigraphy scan?
Imaging tests help doctors see the size, location, and function of your baby's thyroid gland. An ultrasound checks if the gland is in the normal spot, while a highly safe scintigraphy scan shows exactly where the active thyroid tissue is located.
If my baby is diagnosed with congenital hypothyroidism, will they need medication forever?
Not necessarily. Some babies have transient congenital hypothyroidism, which is a temporary condition. Doctors usually treat immediately to protect brain development, but may try pausing medication around age three to see if the thyroid functions on its own.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.What were the exact results of my baby's venous blood test (TSH and Free T4), and how do they compare to the screening results?
  2. 2.Why are you recommending an ultrasound, a scintigraphy scan, or both for my baby?
  3. 3.Does the imaging show that the thyroid gland is in the correct location?
  4. 4.If the imaging looks normal, does that mean my baby might have a transient (temporary) form of the condition?
  5. 5.At what age would we consider a trial of stopping the medication to see if the condition is permanent?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (15)
  1. 1

    Newborn Screening and Molecular Profile of Congenital Hypothyroidism in a Chinese Population.

    Yu B, Long W, Yang Y, et al.

    Frontiers in genetics 2018; (9()):509 doi:10.3389/fgene.2018.00509.

    PMID: 30420871
  2. 2

    Impact of the reduction in TSH cutoff level to 6 mIU/L in neonatal screening for congenital hypothyroidism in Santa Catarina: final results.

    Nascimento ML, Nascimento AL, Dornbusch P, et al.

    Archives of endocrinology and metabolism 2021; (64(6)):816-823.

    PMID: 33085992
  3. 3

    Fifty years of newborn screening for congenital hypothyroidism: current status in Australasia and the case for harmonisation.

    Huynh T, Greaves R, Mawad N, et al.

    Clinical chemistry and laboratory medicine 2022; (60(10)):1551-1561 doi:10.1515/cclm-2022-0403.

    PMID: 35998658
  4. 4

    Evaluation of Transient or Permanent Congenital Hypothyroidism.

    Kurtoğlu S, Baştuğ O, Özdemir A

    Journal of clinical practice and research 2023; (45(4)):321-326 doi:10.14744/cpr.2023.32042.

    PMID: 41255433
  5. 5

    Thyroid Function in Preterm/Low Birth Weight Infants: Impact on Diagnosis and Management of Thyroid Dysfunction.

    LaFranchi SH

    Frontiers in endocrinology 2021; (12()):666207 doi:10.3389/fendo.2021.666207.

    PMID: 34211436
  6. 6

    Prematurity Appears to Be the Main Factor for Transient Congenital Hypothyroidism in Greece, a Recently Iodine-Replete Country.

    Koukkou EG, Girginoudis P, Nikolaou M, et al.

    Nutrients 2025; (17(19)) doi:10.3390/nu17193039.

    PMID: 41097117
  7. 7

    Prevalence of Congenital Hypothyroidism and Efficacy of Current Cord Sample Screening in the Presence of Metabolic Screening: A Retrospective Cohort Study.

    Alwadani IM, Almohammadi AM, Alzamzami WN

    Cureus 2025; (17(2)):e79185 doi:10.7759/cureus.79185.

    PMID: 40115703
  8. 8

    Thyroid imaging study in children with suspected thyroid dysgenesis.

    Chun S, Lee YS, Yu J

    Annals of pediatric endocrinology & metabolism 2021; (26(1)):53-59 doi:10.6065/apem.2040120.060.

    PMID: 33819958
  9. 9

    Infants Diagnosed with Athyreosis on Scintigraphy May Have a Gland Present on Ultrasound and Have Transient Congenital Hypothyroidism.

    McGrath N, Hawkes CP, Ryan S, et al.

    Hormone research in paediatrics 2021; (94(1-2)):36-43 doi:10.1159/000514989.

    PMID: 34044405
  10. 10

    Integrated Diagnostics of Thyroid Nodules.

    Giovanella L, Campennì A, Tuncel M, Petranović Ovčariček P

    Cancers 2024; (16(2)) doi:10.3390/cancers16020311.

    PMID: 38254799
  11. 11

    Complicated Relationship between Genetic Mutations and Phenotypic Characteristics in Transient and Permanent Congenital Hypothyroidism: Analysis of Pooled Literature Data.

    Long W, Zhou L, Wang Y, et al.

    International journal of endocrinology 2020; (2020()):6808517 doi:10.1155/2020/6808517.

    PMID: 32565793
  12. 12

    Case Report: Expanding the Digenic Variants Involved in Thyroid Hormone Synthesis-10 New Cases of Congenital Hypothyroidism and a Literature Review.

    Yang R, Lu Y, Yang C, et al.

    Frontiers in genetics 2021; (12()):694683 doi:10.3389/fgene.2021.694683.

    PMID: 34456971
  13. 13

    Etiological evaluation of primary congenital hypothyroidism cases.

    Bezen D, Dilek E, Torun N, Tütüncüler F

    Turk pediatri arsivi 2017; (52(2)):85-91 doi:10.5152/TurkPediatriArs.2017.3989.

    PMID: 28747839
  14. 14

    Transient Neonatal Hypothyroidism Followed by Hyperthyroidism Due to Maternal Thyrotropin Receptor Antibodies.

    Garrelfs M, Kamp GA, van Trotsenburg ASP

    JCEM case reports 2025; (3(3)):luaf040 doi:10.1210/jcemcr/luaf040.

    PMID: 40061242
  15. 15

    Transient Congenital Hypothyroidism in Turkey: An Analysis on Frequency and Natural Course.

    Kara C, Günindi F, Can Yılmaz G, Aydın M

    Journal of clinical research in pediatric endocrinology 2016; (8(2)):170-9 doi:10.4274/jcrpe.2345.

    PMID: 27086592

This page explains congenital hypothyroidism screening and diagnostic imaging for educational purposes. Always rely on your pediatric endocrinologist or pediatrician to interpret your baby's specific laboratory results and scans.

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