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Practice Practice Pointer

Important considerations for interpreting biochemical tests in children

BMJ 2018; 361 doi: (Published 24 May 2018) Cite this as: BMJ 2018;361:k1950
  1. Khosrow Adeli, head and professor, clinical biochemistry1 2,
  2. Victoria Higgins, PhD candidate1 2,
  3. Karin Trajcevski, clinical research project coordinator, CALIPER Project2,
  4. Mark R Palmert, associate chair of paediatrics and head of endocrinology3
  1. 1CALIPER Program, Paediatric Laboratory Medicine, The Hospital for Sick Children, Toronto, Canada
  2. 2Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada
  3. 3Division of Endocrinology, The Hospital for Sick Children; Departments of Paediatrics and Physiology, University of Toronto, Toronto, Canada
  1. Correspondence to K Adeli khosrow.adeli{at}

What you need to know

  • Clinical laboratories often use thresholds to flag abnormal results but these may not be accurate

  • Appropriate age and sex specific thresholds are sometimes needed

  • Dynamic physiology of children can alter biochemistry, particularly under one year of age and during puberty 

  • Factors such as capillary blood and small volume samples can alter the result

  • Creatinine and alkaline phosphatase are examples of tests that are known to vary

Rapid growth and development during childhood and adolescence pose challenges to paediatric healthcare, including blood test interpretation.1 Physicians may order blood tests in children and adolescents with signs and symptoms suggestive of a health condition.

Blood tests can be used for screening, risk assessment, disease diagnosis or prognosis, and treatment initiation or monitoring (box 1). For example, newborns are commonly screened for metabolic disorders and genetic diseases, including phenylketonuria and congenital heart disease,9 and abnormal results are later confirmed by diagnostic testing.10 Additionally, measurement of bilirubin to test for jaundice is common in newborns. Reference intervals or clinical decision limits are widely used by clinical laboratories to flag results, thereby notifying physicians to potentially follow up with additional medical tests or specialist referral. Depending on an individual’s risk, children and adolescents might also be screened for common conditions including type 2 diabetes, dyslipidaemia, and iron deficiency anaemia, which have all become more common with increased rates of obesity.111213

Box 1

Considerations for requesting blood tests in children

• Laboratory medicine is integral to health assessment in the paediatric population, but important considerations for laboratory testing in this population can often be overlooked.

• Pre-analytical factors can differ compared with an adult population. For example, automated laboratory equipment may not be able to handle small volume specimens, requiring manual processing, leading to difficulties in standardising specimen processing. Small sample volume might also pose challenges to repeat testing to …

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