[Comparative estimation of monocompartmental methods of analyzing 99m-Tc-diethylenetriamine pentaacetic acid clearance by declining plasma levels with special reference to long term studies].

Plasma slope clearance estimation with 99m-Tc-DTPA corresponds to total clearance determination. When activity is measured directly in cumulative serum samples, determination of the plasma slope clearance is suitable for practical applications only if simplified analytic procedures are used. Monocompartmental analytic procedure that take the late slope of the disappearance curve into account are particularly useful for GFR estimation. The A3k3-slope-clearance analysis method is a monocompartmental procedure for determining slope clearance that is based on activity measurements between the 100th (120th) and 240th minute after injection. Compared with other monocompartmental procedures, the A3k3-clearance method shows a highly significant hyperbolic correlation with serum creatinine, a highly significant linear correlation with inulin total clearance, is age dependent and yields reproducible results. The sensitivity (frequency of correct function results in the case of disturbed glomerular function) of the A3k3-slope-clearance method with 99m-Tc-DTPA is particularly good. The practically important predictability of pathological A3k3-clearance results (frequency of correct results when the kidney function is truly reduced) is on the average 85%. The mean efficiency of the method is 88% (65-97% at the 95% confidence-level).