Blood Tests for Children: What Parents Need to Know
Children's blood test results are not the same as adults'. Reference ranges differ by age, some markers are naturally higher or lower, and preparation matters. Here's a parent's guide to paediatric blood testing in Australia.
Common Blood Tests for Children
Children don't need routine blood tests unless there is a clinical concern. The most common reasons a GP or paediatrician orders blood work are recurrent illness, poor growth, suspected nutritional deficiency, or family history of a condition.
| Test | Common Reasons | Age Group | Child vs Adult Ranges | Fasting? |
|---|---|---|---|---|
| Full Blood Count (FBC) | Recurrent infections, fatigue, pallor, bruising, suspected anaemia, fever of unknown origin | All ages | White cell counts higher in children (especially lymphocytes). Haemoglobin norms vary significantly by age — a level of 110 g/L is normal for a 1-year-old but low for a teenager. | No |
| Iron Studies (Ferritin) | Poor growth, fatigue, picky eating, vegetarian diet, heavy periods (adolescents) | All ages (common from 12 months) | Ferritin reference ranges are lower in young children. Iron deficiency is the most common nutritional deficiency in Australian children. | Ideally fasting, but not critical for ferritin alone |
| Coeliac Screen (tTG-IgA) | Failure to thrive, chronic diarrhoea, bloating, abdominal pain, family history of coeliac disease | 12 months+ (must be eating gluten) | IgA levels are naturally low in young children — total IgA should be measured alongside tTG-IgA to avoid false negatives. 1 in 70 Australians has coeliac disease. | No (but must be eating gluten for 6+ weeks before testing) |
| Allergy Panel (Specific IgE) | Suspected food allergy (milk, egg, peanut, wheat), eczema, asthma, allergic rhinitis | All ages (common from 6 months) | IgE levels are lower in infants and increase with age. Results must be interpreted alongside clinical history — a positive IgE does not always mean clinical allergy. | No |
| Fasting Glucose / HbA1c | Type 1 diabetes screening (family history, symptoms), obesity screening, acanthosis nigricans | All ages | HbA1c diagnostic thresholds are the same as adults (≥48 mmol/mol = diabetes). Fasting glucose normal range is similar. Type 1 diabetes is more common in children than type 2. | Yes (fasting glucose). No (HbA1c). |
| Thyroid Function (TSH) | Poor growth, weight gain, delayed puberty, fatigue, family history of thyroid disease | All ages (neonatal screening at birth) | TSH is higher in newborns and decreases with age. A TSH of 6 mIU/L may be normal in a neonate but elevated in a 10-year-old. Age-specific ranges are critical. | No |
| Vitamin D | Dark skin, limited outdoor play, exclusively breastfed infants, bone pain, rickets screening | All ages | Reference ranges are the same as adults (>50 nmol/L adequate). Deficiency is more common in infants who are exclusively breastfed (breast milk is low in vitamin D) and in children with dark skin. | No |
| Kidney Function (UEC) | Recurrent UTIs, haematuria, proteinuria, medication monitoring, suspected kidney disease | All ages | Creatinine and eGFR norms are significantly different in children — paediatric eGFR uses height-based formulas (Schwartz equation), NOT the adult CKD-EPI equation. Adult eGFR calculators are meaningless for children. | No |
How Children's Reference Ranges Differ
Using adult reference ranges for children is a common source of unnecessary worry. Many markers that appear "abnormal" against adult ranges are completely normal for a child's age. Here are the most important differences:
| Marker | Adult Range | Infant Range | Child Range | Why It Differs |
|---|---|---|---|---|
| Haemoglobin (Hb) | 120–180 g/L | 100–140 g/L (6–12 months) | 115–145 g/L (2–12 years) | Physiological anaemia of infancy: foetal haemoglobin is replaced, causing a dip at 2–3 months. Hb gradually rises through childhood. |
| White Cell Count (WCC) | 4.0–11.0 ×10⁹/L | 6.0–18.0 ×10⁹/L (0–12 months) | 5.0–15.0 ×10⁹/L (2–12 years) | Children have a naturally higher lymphocyte count (lymphocyte predominance until age ~5). This is normal, not infection. |
| Alkaline Phosphatase (ALP) | 30–110 U/L | 150–400 U/L | 100–350 U/L | ALP is released from growing bones. High ALP in children reflects active bone growth and is completely normal. It peaks during adolescent growth spurts. |
| Creatinine | 60–110 µmol/L | 15–30 µmol/L | 25–60 µmol/L | Creatinine reflects muscle mass, which is much lower in children. A creatinine of 80 µmol/L is normal in an adult but could indicate kidney problems in a 5-year-old. |
| TSH | 0.5–4.5 mIU/L | 0.7–11.0 mIU/L (0–12 months) | 0.6–6.0 mIU/L (1–5 years) | TSH is higher in neonates (physiological surge at birth) and gradually decreases toward adult levels by mid-childhood. |
| Ferritin | 20–300 µg/L | 50–400 µg/L (birth) | 10–55 µg/L (6 months–5 years) | Ferritin is high at birth (iron stores from mother) and drops during the first year. Iron deficiency is most common between 6 months and 3 years as stores deplete and iron-rich foods may be limited. |
Making Blood Tests Less Scary
Blood tests are stressful for children (and parents). These evidence-based strategies significantly reduce distress and make the experience easier for everyone:
Use numbing cream (EMLA or AnGel)
Apply topical anaesthetic cream to the inner elbow (antecubital fossa) and back of the hand 45–60 minutes before the blood draw. Cover with an occlusive dressing. This significantly reduces pain and distress. Available over the counter at pharmacies in Australia.
Honest, age-appropriate explanation
Never promise "it won’t hurt" — this destroys trust. Instead say: "You’ll feel a small pinch, like a quick squeeze, and then it’s done." For toddlers, explain 5 minutes before. For older children, discuss the day before so they can prepare mentally.
Distraction techniques
Bring a favourite toy, tablet with a game or video, bubbles, or a book. Buzzy Bee (vibrating cold device) is evidence-based and available at many paediatric pathology centres. Looking away from the needle consistently reduces pain perception.
Request a paediatric phlebotomist
Major pathology centres have staff experienced in paediatric venepuncture. They use butterfly needles (smaller gauge), know the best veins in children, and can collect from hand veins if elbow veins are difficult. Book at a centre with paediatric experience.
Hydration is key
Well-hydrated children have plumper, easier-to-find veins. Give plenty of water in the hours before the blood test (even if fasting — water is always allowed). Warm hands improve blood flow and vein visibility.
Shorter fasting windows for children
If fasting is required, paediatric guidelines recommend shorter fasting than adults. Children under 5: 4–6 hours. Children 5–12: 6–8 hours. Adolescents: 8–10 hours. Book the earliest morning appointment to minimise fasting distress. Water is always permitted.
Positive reinforcement after
Praise bravery, regardless of crying or difficulty. A small reward (sticker, treat, special activity) creates a positive association. Avoid saying "be brave and don’t cry" — it’s normal and okay to cry. Focus on "you did it, I’m proud of you."
Consider finger prick for young children
For some tests (HbA1c, glucose, FBC), a finger prick or heel prick (infants) may be possible. The sample volume is smaller, and some children find it less frightening than a needle in the arm. Ask your pathology centre.
Reading Your Child's Results: Common Pitfalls
Always use age-specific reference ranges
A result flagged as "abnormal" on a standard pathology report may be using adult reference ranges. Paediatric results MUST be interpreted against age-specific (and sometimes sex-specific) ranges. Your paediatrician or GP will use the correct ranges — but if you’re reading the report yourself, check which ranges the lab has used.
Don’t panic at high ALP or WCC
Alkaline phosphatase (ALP) in children is routinely 2–4 times the adult upper limit due to bone growth. White cell counts are higher in young children due to lymphocyte predominance. These are the two most common "false alarms" when paediatric results are read against adult ranges.
Iron deficiency is common and treatable
Up to 10% of Australian toddlers have iron deficiency. A low ferritin (<12 µg/L) with a low haemoglobin confirms iron deficiency anaemia. Treatment is straightforward: iron-rich foods (red meat, fortified cereals, legumes) and oral iron supplements if indicated. Response to treatment should be rechecked at 4–8 weeks.
One abnormal result may not mean disease
Children get frequent viral infections, which can transiently affect blood counts, liver enzymes, and inflammatory markers. A mildly abnormal result after a recent cold is usually insignificant. Your GP will consider the clinical context and may recommend repeating the test in 4–6 weeks.
eGFR is NOT valid in children under 18
Adult eGFR formulas (CKD-EPI) are not designed for children and will give misleading results. Paediatric kidney function uses the Schwartz equation, which incorporates height. If your child’s report shows an eGFR from the adult formula, ignore it and ask for paediatric interpretation.
When Should Your Child Have Blood Tests?
Unlike adults, children do not need routine blood screening. Your GP or paediatrician may recommend blood tests if your child has:
Persistent fatigue or pallor
A full blood count and iron studies can identify anaemia, which is common in toddlers and adolescents. Iron deficiency affects energy, concentration, and growth.
Poor growth or failure to thrive
Blood tests screen for coeliac disease, thyroid problems, iron deficiency, and other conditions that affect growth. These are usually ordered alongside a growth chart review.
Recurrent infections
Frequent ear infections, chest infections, or unusual infections may warrant an immune function screen including full blood count, immunoglobulin levels, and sometimes complement studies.
Family history of metabolic conditions
Type 1 diabetes, familial hypercholesterolaemia, haemochromatosis, and coeliac disease all have genetic components. Screening children of affected parents is recommended.
Suspected food allergy
Specific IgE blood tests (RAST) can identify sensitisation to common allergens. Results must be interpreted by a doctor — a positive IgE does not always mean clinical allergy, and skin prick testing may also be needed.
Medication monitoring
Some medications (e.g., anticonvulsants, immunosuppressants, ADHD medications) require regular blood test monitoring for liver function, blood counts, or drug levels.
Related Reading
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Information sourced from the Royal Children's Hospital Melbourne, Australasian Association of Clinical Biochemists (AACB), and RCPA pathology reference ranges. Reference ranges are approximate and vary between labs. SmarterBlood provides health information and AI-powered blood test analysis. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your child's doctor.