Single-sample-clearance determination

The quantification of renal function requiring only one blood withdrawal without an additional gamma-camera study yielding sufficiently accurate results has until now only been possible in adults. The reason was that in children the effect of the small volume of distribution on the measured plasma concentration was not taken into consideration. General validity has been gained for known algorithms (specific for the clearance agent used) by a new calculation principle based on normalization of the plasma concentration with respect to the individual body dimensions. A study in 46 children ranging in age from 9 days to 14 years which compares the results with reference clearance values showed a standard deviation Siy.x of only 8.5% from the line-of-identity (r = 0.94); a analogues comparison in 47 adults yielded a Sy.x of 10.1% (r 0.95). Furthermore, the accuracy of clearance values also in adults, especially in those with impaired renal function, distinctly increases when the new calculation method is applied. In this respect, optimized algorithms for renal clearance determinations using 99mTc-MAG3, which were based on studies under steady-state conditions as the reference, and allow the single blood sampling at any time within a defined time interval, are presented in the appendix. Additionally, age-related standard values from newborns to adults are included. (orig.)