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]

SAQ 2 (10)

An adolescent athlete has a creatinine above the adult upper reference limit. The laboratory also changes chemistry platforms next month. [3] [8]

1. Explain why adult creatinine/eGFR tools mislead in children and adolescents. (4) [3]
2. Outline a safe interpretation sequence for any unexpected paediatric lab flag. (3) [6]
3. What must happen to paediatric intervals when the analyser changes? (3) [8]

Model answer

Creatinine/eGFR. Creatinine reflects muscle mass and GFR. Paediatric eGFR methods such as Schwartz equations are required; adult apps and adult absolute cut-offs misclassify risk. Assess hydration, urine findings, trend and body habitus. [3]

Safe sequence. Confirm identity and sample quality → place in age/sex/assay context → classify RI vs decision limit vs critical value → correlate with the child → retest or treat → communicate and safety-net. [4] [6]

Platform change. Intervals need verification or CLSI-style transference to the new method; CALIPER transfer studies show multi-vendor transfer is possible but not automatic. [1] [8]