 ### Description

Increased urinary excretion of oxalate or urate may be associated with increased risk of nephrolithiasis. Matos et al identified the upper limit of normal (at 95% level) urinary excretion of oxalate and urate relative to urinary creatinine. The authors are from Centre Hospitalier Universitaire Vaudois (CHUV) and Lausanne University in Switzerland.

Parameters:

(1) ratio of urinary oxalate to creatinine as mol/mol

(2) ratio of urinary urate to creatinine as mol/mol

(3) age of the child in years from 0 to 18

Conversion:

(1) 1 mg/dL creatinine = 0.0884 mmol/L

(2) 1 mg/dL oxalate = 0.111 mmol/L (molecular weight oxalic acid 90.04)

(3) 1 mg/dL urate = 0.05948 mmol/L

(4) 1 mg/mg oxalate to creatinine = 1.2556 mol/mol

(5) 1 mg/mg urate to creatinine = 0.6728 mol/mol

Urinary Oxalate to Creatinine Ratio

mathematical model for the 95% line of urinary oxalate to creatinine ratio =

= 0.0570 + ((0.2298 + (0.0329 * ((age in years)^2))) * EXP((-1) * 0.9667 * (age in years)))

If the curve is analyzed in JMP, the following curve is derived:

upper limit of normal reference range for urinary oxalate to creatinine ratio at 95% from 0 to 4 years of age =

= (-0.004516 * ((age in years)^3)) + (0.0420694 * ((age in years)^2)) - (0.145037 * (age in years)) + 0.2654984

upper limit of normal reference range for urinary oxalate to creatinine ratio at 95% from 4 to 6 years of age =

= (0.0005 * ((age in years)^2)) - (0.0095 * (age in years)) + 0.1

upper limit of normal reference range for urinary oxalate to creatinine ratio at 95% from 6 to 18 years: 0.06 mol/mol

Urinary Urate to Creatinine Ratio

mathematical model for the 95% line of urinary urate to creatinine ratio =

= 0.3825 + ((1.3588 + (0.3119 * (age in years))) * EXP((-1) * 0.3520 * (age in years)))

If the curve is analyzed in JMP, the following curve is derived:

upper limit of normal reference range for urinary urate to creatinine ratio at 95% for 0 to 18 years =

= (-0.000278 * ((age in years)^3)) + (0.0138703 * ((age in years)^2)) - (0.234624 * (age in years)) + 1.760508