Newborn Screening: What It Catches, and What It Doesn't

Lead

At the maternity hospital, a nurse hands you a sheet of paper labeled "mass screening." Within a few days of birth, a few drops of blood are collected from your baby's heel and sent to a specialized laboratory.

Most parents receive a notification saying "no abnormalities detected" and move on. What was actually being tested, what a negative result guarantees, and — just as importantly — what it does not guarantee: there is rarely an opportunity to pause and find out.

Newborn screening (NBS) is one of the most favorable cost-benefit interventions in the history of modern public health. It is also specific in scope: the conditions covered are limited, the panel varies by municipality, and false positives carry real costs. This article uses peer-reviewed research and national guidelines to clarify what Japan's NBS program is looking for — and what lies outside its field of view.

The ten principles that built the system

The classic reference point for NBS program design is the 1968 WHO monograph by Wilson and Jungner, Principles and Practice of Screening for Disease [1]. The ten criteria they proposed still underpin newborn screening systems worldwide. In summary:

1. The condition must be an important public health problem
2. An accepted treatment must exist
3. Treatment and diagnostic facilities must be available
4. A recognizable latent or early symptomatic stage must exist
5. A suitable test must exist
6. The test must be acceptable to the population
7. The natural history of the condition must be adequately understood
8. There must be an agreed-upon policy on whom to treat
9. The cost of case-finding must be balanced against total medical expenditure
10. Case-finding must be a continuing process

The selection of conditions for newborn screening is, at its core, a question of whether a disease meets a modern version of these ten criteria: early treatment can prevent irreversible harm, a reliable laboratory test exists, and the public health burden justifies systematic detection at scale.

Japan's tandem mass spectrometry panel: twenty conditions

Japan launched its national NBS program in 1977, initially covering five to six conditions including phenylketonuria [2]. By 2014, tandem mass spectrometry (MS/MS) had been introduced nationwide, substantially expanding the panel [2].

The current list recommended by the Ministry of Health, Labour and Welfare includes twenty conditions, structured as follows [2,3]:

• 17 inborn errors of metabolism detected by MS/MS: amino acid metabolism disorders (phenylketonuria, maple syrup urine disease, and others), organic acid disorders (methylmalonic acidemia, propionic acidemia, and others), and fatty acid oxidation disorders (MCAD deficiency and others)
• 3 conditions detected by conventional methods: galactosemia, congenital hypothyroidism, and congenital adrenal hyperplasia

Japanese pilot data using MS/MS estimated the combined detection rate across all screened conditions at approximately 1 in 9,330 births [4]. One-in-ten-thousand-range incidence is not large in absolute terms, but the public health value of identifying each affected infant before irreversible neurological or metabolic damage occurs is substantial.

An important caveat: not all twenty conditions are screened universally across the country. A distinction exists between primary-panel conditions (implemented by all municipalities) and secondary-panel conditions (implementation varies by region), meaning the scope of testing you receive depends partly on where you live [3]. Additionally, conditions such as spinal muscular atrophy (SMA) and severe combined immunodeficiency (SCID) are being piloted in some regions or offered as optional add-ons, so the landscape is actively shifting beyond the official twenty.

Newborn hearing screening: the second pillar

Alongside the blood-spot panel, a second form of newborn screening takes place in the first days of life: the newborn hearing screen.

Two methods are in common use [5]:

• OAE (otoacoustic emissions): measures sound reflected from the cochlea in the inner ear. Quick to administer, low cost, effective for detecting mild hearing loss. More susceptible to interference from middle-ear fluid.
• AABR (automated auditory brainstem response): measures electrical activity along the brainstem auditory pathway. Preferred for infants in the NICU and for detecting auditory neuropathy spectrum disorder.

The Joint Committee on Infant Hearing (JCIH) 2019 position statement recommends using both methods as appropriate to the infant's situation, including a two-stage protocol when indicated [5].

In Japan, the newborn hearing screening implementation rate has exceeded 80% in recent years, and public funding through municipalities has expanded [6]. However, achieving the guideline-recommended 1-3-6 principle — hearing screen by one month, diagnosis by three months, early intervention begun by six months — for all affected infants remains a challenge due to regional variation in follow-up capacity [5,6].

What the screen does not see

This is the section most worth dwelling on.

NBS casts a detection net over a selected, limited set of conditions. That means:

• Autism spectrum disorder and other neurodevelopmental conditions are not included — they cannot be detected by blood-spot analysis
• Most genetic disorders are not included — targeted genetic testing is a separate process
• Most congenital heart defects are not included — diagnosis relies on cardiac auscultation, echocardiography, and pulse oximetry screening conducted separately
• Visual problems are not included — vision checks are part of routine well-child visits
• Many rare metabolic conditions are not included — MS/MS can only detect disorders that produce specific abnormal metabolite patterns

"No abnormalities on newborn screening" means that the net did not catch this infant for the twenty screened conditions and hearing. It does not rule out developmental or health concerns beyond those domains. The Wilson-Jungner framework [1] is explicit that screening programs are not designed to detect all disease.

It is also worth noting the cost of false positives. High-sensitivity tests like MS/MS will generate some "require repeat testing" results in infants who turn out not to have the condition in question. For families, the period of uncertainty before a repeat test can feel acute. The additional testing burden is real. This is an accepted tradeoff in NBS system design, and it is discussed in comparative analyses of NBS programs worldwide [7]. Neither the tradeoff nor the parental anxiety it produces should be invisible.

Three practical steps

Three things worth knowing now.

First, find out which conditions your municipality screens for, and keep that information with the Maternal and Child Health Handbook (the boshi techo, the standard health record book issued to pregnant women in Japan). The distinction between primary- and secondary-panel conditions, and whether your region participates in optional SMA or SCID pilot screening, is listed on your local government's maternal and child health information pages [3]. Families who move to a different prefecture may find the panel changes — this is worth confirming rather than assuming uniformity.

Second, preserve the screening result notification digitally, not only on paper. Result records can become relevant later, when your child sees specialists in adolescence or adulthood. Photographing the relevant pages of the boshi techo and saving them in a cloud-based parenting record like Memori creates a health information asset that outlasts the original paper.

Third, make sure the correct meaning of "no abnormalities detected" is shared within your household. As noted above, this result does not mean "everything is fine across the board." If developmental concerns arise at well-child visits, those questions are separate from what the NBS covered. Over-relying on a normal NBS result as a general health certificate — rather than understanding it as a specific early-detection net — can delay appropriate follow-up.

Summary

Japan's newborn screening program — twenty conditions via blood-spot analysis and hearing tested by OAE or AABR — is among the most comprehensive in the world [2,5,6]. Its structure reflects the Wilson-Jungner criteria [1]: conditions are included selectively because early treatment can prevent irreversible harm, not because screening is meant to map all possible disease.

Understanding what the screen sees is important. Understanding what it does not see is equally so. A negative result is a genuine basis for reassurance within a defined scope — and it is not a guarantee beyond that scope.

References

1. Wilson JMG, Jungner G. Principles and practice of screening for disease. Public Health Papers No. 34. World Health Organization; 1968. https://iris.who.int/handle/10665/37650
2. Tajima T, Yamaguchi S (eds). Newborn Screening in Japan—2021. Int J Neonatal Screen. 2022;8(1):3. doi:10.3390/ijns8010003. PMID: 35076455.
3. Japan Society for Mass Screening. Clinical Guidelines for Diseases Subject to Newborn Mass Screening 2019. https://www.jsms.gr.jp/
4. Shigematsu Y, Hirano S, Hata I, et al. Newborn mass screening and selective screening using electrospray tandem mass spectrometry in Japan. J Chromatogr B Analyt Technol Biomed Life Sci. 2002;776(1):39–48. doi:10.1016/S1570-0232(02)00077-6. PMID: 12127323.
5. Joint Committee on Infant Hearing. Year 2019 Position Statement: Principles and Guidelines for Early Hearing Detection and Intervention Programs. J Early Hear Detect Interv. 2019;4(2):1–44.
6. Cabinet Office's Children and Families Agency (Kodomo Katei-cho), Japan. Survey Results on the Implementation of Newborn Hearing Screening. https://www.cfa.go.jp/policies/boshihoken/chokakukensa
7. Therrell BL, Padilla CD, Loeber JG, et al. Current status of newborn screening worldwide: 2015. Semin Perinatol. 2015;39(3):171–187. doi:10.1053/j.semperi.2015.03.002. PMID: 25979780.
8. Therrell BL, Padilla CD, Borrajo GJC, et al. Current Status of Newborn Bloodspot Screening Worldwide 2024: A Comprehensive Review of Recent Activities (2020–2023). Int J Neonatal Screen. 2024;10(2):38. doi:10.3390/ijns10020038.