When the Newborn Thyroid Test Works, When It Misses, and What Families Can Do: Lessons from Three New Studies

A plain-language review of 2026 studies from China (Hu et al.), England (Peters et al.), and Pakistan (Rehman et al.)

Three new studies from China, England, and Pakistan show how the newborn heel-prick test for an underactive thyroid helps most babies, yet can miss a rarer form of the condition and sometimes never reaches the families who need it. In the studies, babies who started thyroid medicine early did well, with most growing and developing normally. The studies also point to what hospitals and families can do to make sure no baby slips through.

Why a tiny blood spot matters so much

The thyroid is a small butterfly-shaped gland in the neck that makes hormones the body uses to grow and the brain uses to develop. Some babies are born with a thyroid that does not make enough of these hormones, a condition called congenital hypothyroidism. These babies usually look perfectly healthy at birth, which is exactly why doctors test every newborn: a few drops of blood from the heel, dried on a card, can reveal the problem within days. If the condition is treated early with a daily thyroid hormone tablet called levothyroxine, children can grow and learn like their peers. If it is missed, it can cause lasting harm to growth and learning.

How the test came about, and why it is not perfect

Before newborn screening became routine, families usually learned about the problem only when symptoms appeared, such as constipation, jaundice that would not clear, floppiness, or slow development. These signs are vague and easy to attribute to other things, which is why doctors in China wrote that spotting the condition by symptoms alone is difficult [1]. Thyroid hormone is essential for brain development in the early months, and the Pakistani authors point out that, where screening is routine, it has largely eliminated the severe consequences of untreated disease [2].

Screening for this condition has been going on for decades. China began in the early 1980s, and a hospital in Karachi, Pakistan, started testing newborns in 1987, finding five affected babies among its first 5,000 [2]. Most programmes measure a pituitary hormone called TSH, the body's "go faster" signal to the thyroid, much as a thermostat tells a boiler to fire up. The UK programme works this way, and researchers have studied how well it performs at different cut-off levels [3]. When the thyroid is weak, the signal rises. That makes the test excellent at catching a thyroid that is not working. But there is a rarer form, called central hypothyroidism, in which the thyroid is fine and the problem lies in the brain's control centre, which fails to send the signal. In these babies TSH is not raised, so the usual test cannot see them [4]. A few countries, such as the Netherlands, use a different combination of blood tests that can find them [5], although this brings more false alarms that must be sorted out with follow-up testing [6]. European expert guidelines now ask countries to consider ways of finding the central form [7][8]. Elsewhere, many children are still not tested at all: one estimate quoted in the Pakistani study is that only about 30 in 100 children in the world are screened [9].

There is reason to think early detection pays off. In the Netherlands, children whose central condition was found by screening scored similarly to their own brothers and sisters on thinking and movement tests [10]. By contrast, studies of children whose condition was found only after symptoms appeared, in the United States and in Israel, describe diagnosis that came late; in the Israeli group half of the children were diagnosed after about 50 days [11][12].

What the three studies looked at

The first study, from Gansu Province in northwest China, looked at 757,157 babies screened over three years. Doctors there found 332 with the condition, roughly 1 in every 2,300 babies screened [1]. The question they asked was whether it is possible to tell early which babies will need medicine for life and which will recover.

The second, from four specialist hospitals in England, looked back at 118 children with the rarer central form of the condition, none of whom had been picked up by a newborn test [4]. The third, from a hospital in Karachi, followed 39 babies whose condition was found by the heel-prick test, and checked how they grew and developed [2].

What they found

In China, babies whose condition turned out to be lifelong tended to start with higher TSH readings and lower thyroid hormone levels, and they needed larger doses of medicine as they grew. Babies who had thyroid antibodies in their blood were more likely to recover. The researchers also found that heavier babies were more likely to have lifelong disease, although this comparison involved very few of the smallest babies, so it should be read cautiously. These are patterns, not rules: doctors cannot yet use them to decide for an individual child [1].

In England, the rarer form was usually found late. The typical child was diagnosed at about two months, and 42 of the 118 were diagnosed after their first birthday, some at school age. Nearly all (113 of 118) also had other hormone shortages from the same pituitary gland, and many had had low blood sugar, jaundice, or poor weight gain as newborns, signs that are common in healthy babies too and easy to miss. Babies who were sickest in the first weeks were diagnosed soonest. A third of the children (40 of 118) later needed a formal education support plan [4].

In Karachi, 35 of the 39 babies were diagnosed within two weeks, and most began treatment by then. Of 34 children whose development was checked with a parent questionnaire, 32 (94%) were developing normally, and growth was close to the average for their age [2]. Even so, the programme had weak spots. About one in ten families declined testing, more than nine in ten positive screening results turned out to be false alarms, and one child whose parents declined further testing returned at about ten months with delayed development. Most babies who test positive are not actually affected, which is why a second blood test is always needed to confirm.

What this means for families

If your baby's heel-prick test comes back positive, it is much more likely to be a false alarm than a diagnosis, but it is important to go back for the repeat tests quickly. If the condition is confirmed, the daily tablet works, and the studies support what earlier research found: starting early and at a good dose is linked to better learning outcomes [13]. A trial that compared two starting doses found children grew normally on either one [14]. Regular check-ups matter, because doses change as a child grows and some children can eventually come off the medicine under a doctor's supervision. In Karachi, four of six children tested at three years came off treatment successfully, and two needed to continue [2].

Parents of any newborn who is repeatedly low on blood sugar, stays jaundiced for weeks, or is not growing well should ask whether thyroid and other hormone tests, including the "free T4" test, have been done. A normal newborn heel-prick result does not rule out central hypothyroidism. Some children with the rarer form had thyroid levels that were first read as normal because they were compared with adult ranges instead of children's ranges [4].

It helps to remember that a thyroid problem is not the same as a lifelong problem for every child. Some babies have a temporary form, and the China study suggests practical clues about who they might be, but it does not yet give families a certain answer [1].

To picture what a positive result means, consider the Karachi numbers [2]. Out of every 1,000 babies screened, roughly 18 had a positive first test, but fewer than one was confirmed to have the condition once the second blood test was done; about 1 in 24 positive tests proved real. The second test is the safety net that protects families from unnecessary treatment, and it is also the step that some families skip when they are anxious, far from the hospital, or worried about cost. That step, rather than the heel prick itself, is where the Karachi team sees the greatest opportunity to help more children.

If you are a parent, the studies suggest some good questions to ask your baby's doctors. Has my baby had a repeat blood test? What dose of medicine is my baby on, and when will it be checked again? Who will watch my child's growth and development as they get older? And if my baby has had low blood sugar or jaundice that will not settle, have other hormone levels been checked? None of these questions implies that anything has gone wrong. They simply help you work with the care team to keep your child on track.

What researchers are working on next

Researchers in England say a study of costs and benefits is needed before the UK considers adding tests that can find the central form [15]. They also want better blood markers to tell this condition apart from temporary changes in sick or premature babies, and routine gene testing for families. In China, the next step is a larger forward-looking study that follows children from birth to confirm which early signs predict lifelong disease. In Pakistan, the team calls for a national newborn screening programme, stronger follow-up, and formal developmental check-ups. Long-term studies elsewhere, such as a large Korean cohort, remind us that even well-treated children benefit from developmental monitoring through the school years [16].

For related reading on newborn screening for premature babies, see our article on thyroid screening in preterm infants.

References

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  2. Rehman B, Arif M, Akbar A, et al. Growth and neurodevelopmental outcomes of children with congenital hypothyroidism identified through dried blood spot newborn screening at a tertiary care hospital in Pakistan. Endocrinol Diabetes Metab. 2026;9(5):e70296. doi:10.1002/edm2.70296 ↩
  3. Knowles RL, Oerton J, Cheetham T, et al. Newborn screening for primary congenital hypothyroidism: estimating test performance at different TSH thresholds. J Clin Endocrinol Metab. 2018;103(10):3720-3728. doi:10.1210/jc.2018-00658 ↩
  4. Peters C, Wood C, Law JM, et al. Retrospective, multicentre evaluation of central congenital hypothyroidism in the UK. Eur Thyroid J. 2026;15(3):ETJ260014. doi:10.1530/ETJ-26-0014 ↩
  5. Naafs JC, Verkerk PH, Fliers E, et al. Clinical and genetic characteristics of Dutch children with central congenital hypothyroidism, early detected by neonatal screening. Eur J Endocrinol. 2020;183(6):627-636. doi:10.1530/eje-20-0833 ↩
  6. Stroek K, Heijboer AC, Bouva MJ, et al. Critical evaluation of the newborn screening for congenital hypothyroidism in the Netherlands. Eur J Endocrinol. 2020;183(3):265-273. doi:10.1530/eje-19-1048 ↩
  7. van Trotsenburg P, Stoupa A, Léger J, et al. Congenital hypothyroidism: a 2020–2021 consensus guidelines update—an ENDO-European Reference Network initiative endorsed by the European Society for Pediatric Endocrinology and the European Society of Endocrinology. Thyroid. 2021;31(3):387-419. doi:10.1089/thy.2020.0333 ↩
  8. Persani L, Brabant G, Dattani M, et al. 2018 European Thyroid Association (ETA) guidelines on the diagnosis and management of central hypothyroidism. Eur Thyroid J. 2018;7(5):225-237. doi:10.1159/000491388 ↩
  9. Arrigoni M, Zwaveling-Soonawala N, LaFranchi SH, et al. Newborn screening for congenital hypothyroidism: worldwide coverage 50 years after its start. Eur Thyroid J. 2025;14(1):e240327. doi:10.1530/ETJ-24-0327 ↩
  10. Naafs JC, Marchal JP, Fliers E, et al. Cognitive and motor outcome in patients with early-detected central congenital hypothyroidism compared with siblings. J Clin Endocrinol Metab. 2021;106(3):e1231-e1239. doi:10.1210/clinem/dgaa901 ↩
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  13. Selva KA, Harper A, Downs A, et al. Neurodevelopmental outcomes in congenital hypothyroidism: comparison of initial T4 dose and time to reach target T4 and TSH. J Pediatr. 2005;147(6):775-780. doi:10.1016/j.jpeds.2005.07.024 ↩
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  16. Ha EK, Kim JH, Cha HR, et al. Assessment of neurodevelopment and growth in congenital hypothyroidism: serial 6-year follow-up study of 408 patients. J Clin Endocrinol Metab. 2023;108(12):e1588-e1596. doi:10.1210/clinem/dgad364 ↩