Optimal design of a two-sample test for assessing [125I]iothalamate plasma clearance in peritoneal dialysis.
BACKGROUND
Plasma clearance of a tracer in peritoneal dialysis (PD) can be used to assess treatment adequacy without labour-intensive fluid collections. Accuracy and precision of plasma clearance estimates by the bolus injection technique depend on the estimation accuracy of the area under the concentration curve and the measurement precision of plasma concentrations. The first source of error is due to oversimplified, e.g. monoexponential, descriptions of plasma disappearance curves. The second source of error arises from the propagation of measurement errors to the parameter estimates.


METHODS
The theoretical bias of parameter estimates is determined first for a monoexponential approximation of a biexponential disappearance curve and as a function of the first sampling time at which mixing is still incomplete. The precision of plasma clearance estimates, expressed as coefficient of variation, is then described as a function of the experimental variables and of the standard deviation of measurement error. This allows the determination of the optimal two-sample test that yields most precise estimates of plasma clearance.


RESULTS
The optimal two-sample schedules for assessing plasma clearance of [125I]iothalamate in PD patients vary between subjects according to individual clearances and distribution volumes. Our results suggest collecting the first sample 120 min, and the second 2-4 days, after the bolus injection.


CONCLUSIONS
The proposed two-sample test is suitable to be used in clinical routine for assessment of adequacy of PD treatment but requires a priori estimation of individual tracer kinetics and of laboratory measurement errors. A fixed design with the first sample taken after 120 min and the second sample collected 3 days after the bolus injection should yield the best performance.
Institute of Systems Science and Biomedical Engineering, LADSEB-CNR, Padova, Italy.
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D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016477:Artifacts; D005069:Evaluation Studies as Topic; D006801:Humans; D007457:Iodine Radioisotopes; D007483:Iothalamic Acid / Q000493:pharmacokinetics*; D008875:Middle Aged; D010530:Peritoneal Dialysis; D012107:Research Design; D013997:Time Factors; D016896:Treatment Outcome
D007457:Iodine Radioisotopes; D007483:Iothalamic Acid