Toxin Zoomer reference ranges were established using a cohort of apparently healthy adults over 18 years of age. Pediatric reference ranges are not currently available, including for urine creatinine. Therefore, additional context is important when interpreting Toxin Zoomer results in infants and toddlers.
Why might urine creatinine differ in infants and toddlers?
First morning urine creatinine is influenced by urine concentration and should not be interpreted as a direct measure of kidney filtration. This is especially important in young children, whose urine-concentrating ability is still developing. Infants and young children generally approach adult-level urine-concentrating capacity around 1–2 years of age. As a result, urine creatinine concentrations in this age group may reflect age-related developmental and hydration factors in addition to other sources of biological variability.
Collection conditions can also be less standardized in infants and toddlers. Obtaining a true first morning void may be difficult in children who are still in diapers, are newly toilet-trained, or receive fluids or feeds overnight. These factors can affect urine concentration and, consequently, first morning urine creatinine.
Does urine creatinine indicate kidney function?
Serum creatinine and first morning urine creatinine measure different things and should not be compared with or substituted for one another. Serum creatinine is commonly used in the assessment of kidney filtration, whereas the creatinine concentration of a first morning urine specimen is strongly influenced by how concentrated or dilute the urine is.
Therefore, a normal or abnormal serum creatinine result does not predict what first morning urine creatinine will show, and first morning urine creatinine should not be used by itself to assess kidney filtration or kidney function.
How should pediatric Toxin Zoomer results be interpreted?
Because Toxin Zoomer pediatric reference ranges have not been established, providers may consider age-matched population biomonitoring data as additional context when evaluating pediatric results.
For children ages 3–5 years and older, age-stratified data are available through the CDC's Fourth National Report on Human Exposure to Environmental Chemicals, Updated Tables, March 2021 for many- but not all- of the heavy metals and environmental chemicals measured by Toxin Zoomer. NHANES does not conduct biomonitoring for mycotoxins, so comparable NHANES pediatric data are not available for those analytes.
Age-matched comparisons can be particularly important because biomarker concentrations may vary substantially with age. For some analytes, younger children may have higher measured concentrations than older children or adults, although this pattern is not consistent across all analytes. Nationally representative, age-stratified data can therefore provide more appropriate context than directly comparing a young child's result with an adult population.
Key takeaway
Toxin Zoomer results in infants and toddlers should be interpreted cautiously because the test's reference ranges- including urine creatinine- were established in adults. First morning urine creatinine in young children may be affected by developmental differences in urine-concentrating ability, hydration, and the practical challenges of obtaining a standardized first morning specimen. When available, age-matched population data may provide useful additional context for individual analytes, but they do not replace clinical interpretation by the patient's healthcare provider.