Table 3. Reference intervals of urinary creatinine (n = 106).

Reference interval	2.5th quantile (90% CI), ng/mg Cr	50th quantile (90% CI), ng/mg Cr	97.5th quantile (90% CI), ng/mg Cr	CI:RI ratio
Urinary Cr (mg/ml)
Age 1–4 years	0.47 (0.19–0.74)	0.71 (0.54–0.93)	1.59 (1.21–2.09)	0.78
Age 5–8 years	0.69 (0.53–0.86)	0.97 (0.81–1.16)	2.00 (1.70–2.36)	0.51
Age 9–12 years	0.92 (0.80–1.04)	1.32 (1.12–1.56)	2.52 (2.24–2.84)	0.38
Age 13–16 years	1.15 (0.97–1.34)	1.80 (1.41–2.31)	3.17 (2.63–3.81)	0.59

95% RIs along with median values and their 90% CIs for urinary creatinine in the UK cohort were derived using quantile regression methodology.

CI: Confidence interval; Cr: Creatinine; RI: Reference interval.