Determining urinary calcium/creatinine cut-offs for the paediatric population using published data.
BACKGROUND
The purpose of this study was to determine a cut-off above which a result is considered abnormal for 'spot' calcium-to-creatinine ratio (Ca/Cr) in urine in the paediatric age group. While the cut-offs are not well established, there are many published reports of urine Ca/Cr excretion ratio in the literature. Rather than undertaking a difficult, time-consuming, expensive, and ultimately redundant study, an analysis of these published works was undertaken to determine urine Ca/Cr cut-offs for the laboratory.


METHODS
Fourteen studies reporting urine Ca/Cr ratio available in the literature were reviewed. Each study was abstracted for several characteristics. The data were plotted and the line of best fit describing the data was determined. Using the function describing the line, cut-offs by pertinent age were recalculated. These cut-offs were then compared to the original data and to in-house data.


RESULTS
The function describing the line of best fit was y=-0.3175 ln(x) +1.46 (y=Ca/Cr in mmol/mmol and x=age in years), r2=0.85. After consultation with the paediatric nephrologists and comparison with our in-house data, cut-offs for age groups of <1, 1-<2, 2-<5, 5-<10, and 10-18 years in mmol/mmol of 1.50, 1.25, 1.00, 0.70, and 0.60, respectively, were derived.


CONCLUSIONS
Using data from 14 published studies, suitable spot urine Ca/Cr cut-offs from birth to 18 years of age were determined.
Metz
Michael P
MP
Division of Laboratory Medicine, Core Laboratory, Women's & Children's Hospital, 72 King William Road, North Adelaide, South Australia 5008, Australia. michael.metz@cywhs.sa.gov.au
D000293:Adolescent; D000367:Age Factors; D035843:Biomedical Research / Q000379:methods; D002118:Calcium / Q000652:urine*; D002648:Child; D002675:Child, Preschool; D003404:Creatinine / Q000652:urine*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D010372:Pediatrics / Q000379:methods; D012196:Review Literature as Topic
D003404:Creatinine; D002118:Calcium