At about day five, a midwife sits down with a small card, pricks the side of your baby's heel, and presses out a few drops of blood. The card goes off to a regional lab. A few weeks later, you usually hear nothing — which is the normal result. The test screens for nine rare conditions where catching them in the first weeks changes everything about the outcome. Knowing what each one is and why it's on the list helps make sense of what you're agreeing to. For a comprehensive overview, see our complete guide to child health. Healthbooq covers newborn screening in the first weeks.
How and When It's Done
The test is offered at day five of life — usually by the community midwife at home, sometimes on the postnatal ward if you're still in hospital. The midwife warms the heel briefly, makes a small prick on the side of the heel (not the centre — that area has more nerves and is less safe), and collects four or five drops of blood onto an absorbent card with circles to fill.
The day-five timing isn't arbitrary. Several of the conditions tested produce abnormal levels of substances that only build up after the baby has fed for a few days; an earlier sample misses them. Some conditions also need to be tested before the baby is sent home from a NICU stay, in which case the timing is adjusted.
What helps with the prick:
- Feed beforehand. A fed, calm baby handles it better.
- Breastfeed during the test if you can. Or offer a dummy. Either reduces the pain response measurably — there's good trial evidence for this.
- Skin-to-skin if breastfeeding isn't an option.
- Warm the heel first — the midwife will usually do this, but it makes the prick smaller and the bleeding more cooperative.
Most babies cry briefly and settle within a minute or two. The card goes off; you carry on with the day.
Hearing the Result
Results come back in four to six weeks, sometimes sooner. No news is good news. If the screen is normal, there's no phone call — the result goes into the records and you'll see it referenced at the eight-week check.
If something is flagged, the screening team or your GP will contact you within days of the lab result, usually with an appointment for follow-up testing. The follow-up call comes promptly precisely because of the conditions on the list — early treatment is what makes the screen worthwhile.
What Each Condition Is
Nine conditions are currently included in the NHS programme:
Phenylketonuria (PKU). A metabolic condition where the body can't break down phenylalanine, an amino acid present in protein. Untreated, the build-up causes severe and irreversible intellectual disability. Treated from infancy with a tightly controlled phenylalanine-restricted diet, affected children develop normally. Frequency: around 1 in 10,000 births.
Congenital hypothyroidism. The thyroid gland is absent, underdeveloped, or non-functioning, so thyroid hormone levels are inadequate from birth. Untreated, this causes growth failure and intellectual disability. Treated with daily thyroxine tablets, the outcome is fully normal. Frequency: around 1 in 3,000 births — the commonest of the conditions screened.
Sickle cell disease. An inherited haemoglobin disorder, predominantly affecting people of African, Caribbean, Mediterranean, Middle Eastern, and Asian heritage. Causes painful crises, anaemia, and a high risk of life-threatening bacterial infection — particularly pneumococcal — in early childhood. Diagnosis from the heel prick allows daily preventive penicillin from three months of age, which alone has dramatically reduced mortality in affected children.
Cystic fibrosis (CF). A multi-system genetic condition affecting lungs and digestion. Early diagnosis means specialist CF-centre care from birth, before lung damage starts to accumulate. Outcomes are now substantially better than even a generation ago, and early diagnosis is part of why.
MCADD (medium chain acyl-CoA dehydrogenase deficiency). A metabolic condition where the body can't use fat for energy normally during fasting. The first sign in an undiagnosed child is often a hypoglycaemic collapse during an ordinary childhood illness — sudden, severe, occasionally fatal. With the diagnosis in advance, parents are taught to avoid prolonged fasting and to seek early medical help during illness; the condition becomes very manageable.
Maple syrup urine disease. A rare inherited inability to process certain amino acids. Untreated, it causes brain injury within days. Treated with a specialised diet started immediately, outcomes are good.
Isovaleric acidaemia. Another inherited metabolic condition where a specific amino acid breakdown fails. Untreated, dangerous metabolic crises in infancy; treated with diet and supplements, manageable.
Glutaric aciduria type 1. Inherited metabolic condition affecting the brain. Crises are triggered by infections; pre-diagnosis allows protective measures and good outcomes.
Homocystinuria. Inherited disorder of methionine metabolism. Untreated, intellectual disability and vascular complications; with diet and B6/B12 supplementation started early, normal development.
The pattern across all nine: rare individually, serious if missed, and substantially preventable when caught at five days rather than at presentation.
What an Abnormal Result Actually Means
The first thing to know about screening tests: they're deliberately tuned to be sensitive rather than specific. Better to flag a few healthy babies for further testing than to miss the rare baby with the condition. So an abnormal screen is not a diagnosis — it's a flag that further testing is needed, and a meaningful proportion of abnormal screens turn out to be false positives on confirmatory testing.
Two specific points worth knowing:
- Sickle cell screening also detects carriers. Sickle cell trait (one copy of the affected gene) is not the disease — carriers are usually healthy. The result is reported because it has implications for genetic counselling and family planning, not because the child is unwell.
- Cystic fibrosis screening uses a two-step process. A high IRT (immunoreactive trypsinogen) on the blood spot prompts genetic testing on the same sample for the common CF mutations. A positive screen there triggers a sweat test, which is the diagnostic gold standard.
If you do get the call, follow-up is normally within a few days. Bring a notepad — the conversations move fast and you'll want notes — and ask for written information about the suspected condition before the appointment if possible.
Declining the Test
The test is offered, not mandatory. Parents can decline some or all of the conditions, though the vast majority accept the screen. The decision should be informed; midwives and health visitors will discuss any specific conditions on request. Some parents have reservations about being tested for sickle cell carrier status because of the family-history implications — that part of the screen can be declined separately if you wish.
The single piece of context worth knowing: every condition on the list is included only because the evidence shows that screening at five days, with treatment started before symptoms appear, produces a substantially different life for the small number of children affected. The conditions are rare. The benefit, when it lands, is large.
Key Takeaways
The newborn blood spot test is offered to every baby in the UK at five days of age. Four or five drops of blood from a heel prick are sent to a regional lab and screened for nine conditions: PKU, congenital hypothyroidism, sickle cell disease, cystic fibrosis, MCADD, and four other inherited metabolic conditions (maple syrup urine disease, isovaleric acidaemia, glutaric aciduria type 1, homocystinuria). Each was chosen because it's rare but serious, and because early treatment prevents harm that can't be undone once symptoms appear. Most results are normal and parents simply hear nothing. An abnormal screen is not a diagnosis — it means a follow-up test is needed, and most turn out to be false positives or, in the case of sickle cell, carrier rather than disease. Breastfeeding or a dummy during the prick reduces the pain meaningfully.
