Child Health Blood Tests: A Parent's Guide

Why Children Need Blood Tests

Routine blood tests in childhood help catch growth, nutrition and developmental issues early, when they're easiest to treat. Most healthy children need far fewer tests than adults.

Newborn Screening

Performed within the first days of life, newborn screening checks for rare but serious genetic, metabolic and hormonal conditions (such as congenital hypothyroidism and PKU) via a simple heel-prick blood sample.

Common Tests by Age

Common Reasons for Testing

• Unexplained fatigue or paleness (anaemia screening)
• Growth concerns
• Recurring infections
• Family history of a genetic or metabolic condition
• Before starting certain medications

Tips for Parents

• Explain the test simply and honestly to reduce anxiety
• Bring a comfort item or distraction for younger children
• Ask the lab about paediatric-specific needles or numbing cream if needed
• Most routine paediatric blood tests use very small sample volumes

Frequently Asked Questions

Why children's reference ranges are not adult ranges

Applying adult reference intervals to children produces both false alarms and missed abnormalities, because several analytes change markedly with age. Alkaline phosphatase runs several times the adult upper limit during growth and peaks in adolescence. Haemoglobin is high at birth, falls to a physiological trough around two to three months, then climbs slowly through childhood and diverges by sex at puberty. Lymphocytes outnumber neutrophils for the first years of life, which reverses the adult differential and is entirely normal. Creatinine is low simply because muscle mass is low. Any report on a child should be read against paediatric, age-banded ranges.

Making the blood test itself easier

• Topical anaesthetic cream applied 30 to 60 minutes beforehand genuinely reduces pain and is widely available; ask when booking rather than on arrival.
• Honest, simple explanation shortly before, rather than days ahead for young children, avoids prolonged anticipatory anxiety.
• Comfort positioning, with the child sitting on a parent's lap and held securely, is less distressing than lying flat.
• Distraction with a screen, bubbles or a book measurably reduces distress and is not a trivial extra.
• Hydration beforehand, where fasting is not required, makes the vein easier to find and the attempt quicker.

Tests parents most often ask about

Iron deficiency is the commonest nutritional problem in young children, particularly where cow's milk has displaced iron-rich foods, and presents with pallor, irritability and poor appetite rather than dramatic symptoms. Coeliac disease is worth considering in a child with faltering growth, chronic loose stools or unexplained iron deficiency, and the serology must be taken while gluten is still being eaten. Thyroid testing is appropriate for growth failure or unexplained weight change. Vitamin D deficiency is common in children with limited sun exposure and in exclusively breastfed infants not receiving supplementation.

When to seek help rather than a test

Some presentations need assessment now, not a blood form. A fever in an infant under three months, a non-blanching rash, breathing difficulty, drowsiness or unresponsiveness, a seizure, refusal to feed with reduced wet nappies, or a child who simply looks seriously unwell to a parent all warrant urgent review. Parental instinct that something is badly wrong is a recognised warning sign and should not be talked down.

References

Sources cited on this page. PubMed links open the original abstract.

1. Bright Futures / American Academy of Pediatrics. Recommendations for Preventive Pediatric Health Care. Pediatrics. 2016;137(1):e20153908. PMID 26700653 · doi:10.1542/peds.2015-3908

Interpreting Children's Blood Test Reference Ranges

The most important principle when reviewing a child's blood test is that reference ranges differ substantially from adult values – and differ between children at different developmental stages. Haemoglobin, for example, falls to a physiological nadir around two to three months of age (the "physiological anaemia of infancy"), then rises progressively through childhood; the adult male range of 130–175 g/L does not apply to a five-year-old. Similarly, white cell counts are higher in infants and younger children, alkaline phosphatase (ALP) is markedly elevated during active bone growth, and TSH reference intervals narrow as thyroid development completes in the first years of life.¹

Always compare your child's result against the laboratory's age-specific reference range printed on the report, not against ranges you find online or from adult tables. When a result is flagged as outside the reference interval, context matters: was the child unwell at the time of the test? Dehydration, fever, and crying during venepuncture all produce transient changes – particularly in white cell count and cortisol – that resolve once the child recovers.

Common Tests Ordered for Children and What They Indicate

The full blood count (CBC) is the most frequently requested paediatric test. In children, it helps identify iron-deficiency anaemia – the most common nutritional deficiency globally in children aged one to five – as well as infections, leukaemia, and clotting problems. A low MCV (mean corpuscular volume) with low haemoglobin typically points to iron deficiency or thalassaemia trait; the two are distinguished by serum ferritin and haemoglobin electrophoresis.

Thyroid function (TSH and free T4) is checked in the newborn screening programme (heel-prick test) and again if growth faltering, constipation, or learning difficulties raise clinical concern. HbA1c and fasting glucose are used to screen for and monitor type 1 diabetes, which accounts for the large majority of paediatric diabetes diagnoses. Liver function tests are requested if jaundice persists beyond the neonatal period, if abdominal symptoms suggest liver disease, or before starting enzyme-inducing medications such as anti-epileptics. Renal function (creatinine, urea, cystatin C in younger children) is monitored in congenital kidney anomalies and urinary tract infections with recurrence risk.²

What to Expect During Paediatric Blood Collection

For most children, blood is taken from a vein in the antecubital fossa (inner elbow) using a small-gauge needle, or by heel-prick for neonates and some infants. Topical anaesthetic cream (EMLA or Ametop) applied 30–60 minutes before the test substantially reduces pain and distress and is standard practice in paediatric services. Keeping the child calm, warm, and well-hydrated before the test makes venepuncture easier and reduces the need for repeat attempts. Distraction techniques – blowing bubbles, screens, or counting – are evidence-based and meaningfully reduce perceived pain.³

Capillary blood from a finger-prick is an alternative for some tests and is less distressing for older children who are needle-averse. Point-of-care devices can measure haemoglobin, blood glucose, and CRP from a finger-prick sample with results available within minutes. Discuss with your paediatrician or phlebotomist whether a capillary sample is suitable for the specific tests being requested.