Appendix 4.

Scenario 4. MU of calculated creatinine clearance (u_CrCl).

Calculation of creatinine clearance (Clcr)	$\frac{\text{Urine\hspace{0.17em}creatinine\hspace{0.17em}}(\mu \text{mol}/\text{L})\times \text{Urine\hspace{0.17em}volume\hspace{0.17em}}(\text{mL})}{\text{Plasma\hspace{0.17em}creatinine\hspace{0.17em}}(\mu \text{mol}/\text{L})\times \text{Collection\hspace{0.17em}time\hspace{0.17em}}(min)}$
Results for 68-year-old woman.	Plasma creatinine: 92 μmol/L, SD: 2.26 (QC), CV: 0.0246 Urine creatinine: 2560 μmol/L, SD: 340 (QC), CV: 0.1328 Urine volume 2683 mL, SD: 25 (estimate), CV: 0.0093 Collection time: 24 h (1440 min), SD: 30 (estimate), CV: 0.0208
Creatinine clearance.	$\frac{2560\times 2683}{92\times 1440}=51.8\hspace{0.17em}\text{mL}/min$
MU of Clcr calculated as square root of sum of squares of MUs of contributing results	uCrCl = (u2UCreat + u2UVol+ u2PCreat+ u2Time)1/2
Creatinine clearance calculated using division and multiplication; therefore must calculate uCrCl using CVs.	CVCrCl = (CV2UCreat + CV2UVol + CV2PCreat + CV2Time)1/2 = (0.02462 + 0.13282+ 0.00932 + 0.02082)1/2 = 0.137
SD = measurement result x CV.	SD = 51.8 mL/min x 0.137 = 7.096 mL/min = uCrCl
Coverage factor k = 2.	UCrCl = 14.192 mL/min
Result rounded for clinical use	UCrCl = 14.2 mL/min
Patient result.	51.8 ± 14.2 mL/min (95% coverage probability)