Over the last year, I’ve seen paediatric patients with various presentations (alopecia, behavioural issues etc.) whose thyroid results have seemed out of whack e.g. TSH values in the 3s and 4s.  I noticed as well that each pathology company provided a slightly altered reference range but on the whole they weren’t significantly different from expected adult results (0.4-4.8 mU/mL). It left me wondering if there should be in fact specific reference ranges for kids given the striking developmental endocrine milieu.  So began a brief search of the scientific literature and lo and behold (!) there is such a thing and guess what?  Kids’ thyroid results do differ from adult ones!!  One piece of research that was intended to establish kids’ reference ranges was conducted in Austria, where routine results (serum TSH, fT3, and fT4) were collated from existing laboratory data of 2,194 serum samples from a hospital based population of children aged 1 day – 18 years (Kapelari et al. 2008 Pediatric reference intervals for thyroid hormone levels from birth to adulthood: a retrospective study. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2645400/)) Granted, these children are in hospital and yet deemed ‘healthy’ – which is a bit befuddling, however, the ranges found by these researchers were consistent with other previous studies in different cohorts, which adds strength to their findings.  They revealed that TSH should be highest at birth and in the first month (e.g. 3.5 is the 50th percentile for this age group) and progressively decline throughout childhood and adolescence.  So 50th percentile results across the age groups looks like this:


TSH 50th percentile values

TSH Range




















While there is a clear pattern of declining TSH with age throughout childhood, there were less changes across the ages with regard to fT4 and fT3 values, with the 50th percentile value for fT4 being approx. 15 pmol/L in all ages except 1mo and fT3 being high 5s to mid 6s.  These are more robust values than we’ve come to expect and accept in many of our adult patients.

So next time you see thyroid results for a child – check out where they sit according to these percentiles, because where there’s smoke there’s typically a fire and further investigation of a marginally high TSH can reveal, antibodies, incorrect T4/T3 ratios and deficiencies of critical thyroid nutrients which might be central to helping resolve the health issues.