Interpreting common paediatric laboratory reference ranges — formative SAQs

SAQ 1 (10)

A thriving 4-year-old has ALP well above the adult upper limit, normal bilirubin and GGT, and a normal examination. A separate neonate on day 2 has a neutrophil count that would be high for a school-age child. ^{[2] [5]}

1. Define reference interval, decision limit and critical value. (3) ^{[4] [6]}
2. Interpret the ALP result and outline your next steps. (4) ^[2]
3. State how day-of-life changes neonatal haematology interpretation. (3) ^[5]

Model answer

Threshold triad. A reference interval describes usual values in a defined population (often central ~95%, age/sex partitioned). A decision limit changes action (for example jaundice phototherapy pathways). A critical value requires urgent closed-loop clinician notification because delay risks harm. ^{[4] [6] [7]}

ALP. Bone growth commonly elevates ALP in children; with normal cholestatic markers and a thriving child, avoid automatic biliary imaging. Review the full liver panel, growth, symptoms and medications; recheck or investigate only if the pattern or child is concerning. Cite paediatric ALP interval evidence rather than adult cut-offs. ^[2]

Neonatal neutrophils. Expected neutrophil concentrations swing across the first hours and days of life; interpret against neonatal day-of-life expectations plus the whole baby, not school-age bands. ^[5]