Determination of 99mTc‐DTPA clearance by a single plasma sample method

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Abstract
To derive a formula for determnation of 99mTc-DTPA clearance (Cl) from the radioactivity in a single plasma sample, the relation Cl=ECV/.hivin.t was used, where ECV is the extracellular volume and .hivin.t is the mean transit time of the tracer in the organism. By studying the 99mTc-DTPA time activity curves of 45 consecutive patients we found that ECV could be estimated from the body surface area, and that .hivin.t could be calculated from the radioactivity in a single plasma sample. Cl calculated by the single sample method was almost identical to Cl calculated by a standard multiple sample method (r=0.987). It is concluded that the single sample method is accurate and that it may prove useful as a routine method provided that (a) the method is not used in patients with 99mTc-DTPA clearance less than 30 ml min-1, since this investigation includes only patients with Cl > 30 ml min-1; (b) the method is not used for children, since the test material did not contain any children; (c) the method is only used for plasma samples drawn at 180 .ltoreq. t .ltoreq. 300 min.