Defining pediatric reference ranges in laboratory medicine: Why adult ranges don t always work Children are not small adults Michael J. Bennett PhD, FRCPath, FACB DABCC University of Pennsylvania & Children s Hospital of Philadelphia ASCLS August,2016 Dr Bennett has no conflicts of interest to declare Goals Define primary physiological differences between newborn/pediatric and adult populations How are samples collected from children and what are the limitations Why do these limitations create difficulties Describe ongoing studies to generate pediatric reference ranges Introduce a new initiative Size of the patient population is different Adult population generally ranges from 50kg 250kg plus (5 fold difference in range) Many of original published reference ranges were based on the 70kg adult. Including (e)gfr Pediatric population weighs in at less than 1kg and may extend to 70kg plus (70 fold difference in range) And size matters Most of the specialist requirements for a pediatric service occur because of very small neonates and sick infants But we also need to take into account the whole concept of growth and development in older children Much as they will deny it, teenagers are rarely fully developed! Immature organ systems in the newborn Immature organ systems in the newborn Lungs Need for newborn to adapt to extra uterine life Impacts measurement of blood gases, ph Neonates have wider ranges of blood gas and ph values than adults ph effects binding of drugs /metabolites to proteins. Therefore need for different therapeutic ranges for some drugs antiepileptics In todays environment, developing appropriate reference intervals for neonates unlikely to impact therapy Kidney Many newborns (including term) have both immature glomerular function and immature tubular function. Outcome is wide fluctuations in electrolyte balancecan quickly change from hypo to hypernatremia. Very difficult to measure renal function Clearance of drugs impacted Management in clinically significant situations unlikely to change but norms based upon norms that have ben derived from adult practice. 1
Immature organ systems in the newborn Immature organ systems in the newborn Liver Immature enzyme systems Immature fasting systems such as results in hypoglycemia a phenomenon known as physiologic hypoglycemia possibly secondary to abnormal insulin responses Altered drug metabolism Failure to conjugate bilirubin Hematologic Change over from intrauterine oxygen transport (fetal hemoglobin) to extrauterine hemoglobin results in high bilirubin production and physiological jaundice. Immature liver fails to adequately conjugate this bilirubin Developmental changes through childhood Developmental changes through childhood Alkaline phosphatase reference values Bone Growth Markers of Bone Growth follow growth spurts in children Alkaline Phosphatase N and c terminal procollagen peptides 2
Developmental changes through childhood Testosterone through life Endocrine Puberty and the development of secondary sexual characteristics Males: go from very low circulating androgen levels (difficult to measure) to high levels Females: Develop menarche with circadian changes to reproductive hormones Because of circadian variation and variable onset of sexual maturity, good normal reference ranges are desperately needed to identify pathological conditions Estrogen through life Prematurity creates additional problems Lungs; insufficient surfactant Kidney; even less prepared to balance electrolytes Liver; enzymes just not ready to face the world. Really poor at handling bilirubin GI tract; not prepared for enteral feeding at risk for necrotizing enterocolitis Hematologic; not ready to switch off fetal hemoglobin leads to worse respiratory problems Practical issues for small patients % of total blood volume represented by a 10mL draw Small blood volume Maximum that can be drawn Method of collection 3
Newborns and infants have high hematocrits Method of blood collection is often different in pediatrics Venipuncture, most common in adults. Easy access to big chunky veins Arterial collection, more common in pediatrics. Especially blood gases Capillary, most common in small children Drawing from a line, not recommended but very frequently used in pediatrics. Frequent cause of pre analytical error Different draw types : different reference ranges Current ways in which to establish a pediatric reference range Develop an in house range based on your own pediatric population Pro: Will serve the local population well Con: Do you have enough normal patients? Will only apply to current instruments Current ways in which to establish a pediatric reference range Use published data Pro: Does not require you to do it yourself Con: Only applies to instrumentation used for published literature/books Generally limited in terms of analytes Needs to be validated against your own patient population How to do an in house pediatric reference range Take all values for a given analyte and remove outliers for statistical analysis assumes most patients are normal and outliers do not count. Select a particular clinic that may only have normal patient; presurgical clinic for elective procedures will take a very long time and there will be few young infants. 4
Large ongoing studies CALIPER Caliper Canadian Laboratory Initiative on Pediatric Reference Intervals KiGGS German Health Interview and Examination Survey for Children and Adolescents CHILDx ARUP initiative AACC Pediatric Reference Range Committee NIH National Children s Study 8,500 healthy, non hospitalized children across Canada volunteers attracted through promotions 100 biomarkers using several analyzers Chemistry and Hematology Combined pediatric data with adult data Data is readily available outside of Canada CALIPER CALIPER KiGGS CHILDx Started program in 2003 18,000 girls and boys Multiple health related outcomes Pediatric reference values one outcome Goal is to follow prospectively to look for health related trends BMC Public Health DOI 10.1186/1471 2458 8 196 2008 Started in 1999 Two cohorts: 6 months to 6 years (240M/F each year0 7years to 17years (120M/F per year plus anthpometrics, Tanner stage 5
CHILDx Currently 85% sample collection complete for younger group 35/66 analytes completed 100% sample collection complete for older group 58/144 analytes completed Multiple publications in scientific literature accessed through ARUP website Ongoing AACC activities to develop pediatric reference ranges AACC established a Pediatric Reference Range Committee (PRRC) 2008 Charged with evaluating potential sources of normal pediatric laboratory data that can be universally used as age, sex and ethnically appropriate basis on a national or potentially global scale The National Children s Study ( NIH) The National Children s Study Was developed to prospectively monitor development from birth to 20 years of age of 100,000 American newborns Cross sectional, covers all ethnic groups Covers rural/urban distribution Multiple sampling times throughout life Goal is to identify determinants of optimal childhood development and health AACC Pediatric reference range committee advising NCS on sample collection, storage techniques. Developed a protocol for reference range collection After two years of sample collection; Congress removed funding for the project The PRRC had two options National Children s Study samples Two years of samples had been collected from the youngest cohort of normal infants including newborns Blood spots had been collected Increasing amount of evidence that many important biomarkers are stable and measurable in blood spots 6
Work in progress The end. Thank you for your attention Blood spots were obtained from the NCS Funding by AACC For mass spectrometric analysis of groups of biomarkers to represent nutritional and endocrine reference ranges Dennis Dietzen St Louis Children s Patti Jones Children s Medical Center Dallas 7