REPRODUCIBILITY OF A SINGLE-SAMPLE METHOD FOR TC-99(M)-MAG3 CLEARANCEUNDER CLINICAL CONDITIONS

The aim of this study was to assess the intra-individual reproducibili ty of Tc-99(m)-mercaptoacetyltriglycine (Tc-99(m)-MAG3) clearance in r outine clinical practice in various circumstances using a single-sampl e method. Three groups of 30 patients each were enrolled in the study. Investigations were repeated on the same day with two different level s of activity (group A), within 1 week (group B), or after 1 year (gro up C). Blood samples were taken after 20 and 25 min and clearance valu es were averaged to minimize incidental errors after calculation accor ding to the formula proposed by Bubeck et nl. For clearance estimation on the same day, time-dependent background correction for residual ac tivity was carried out. The mean difference was -2.0%, +6.0% and -1.5% (S.D. = 6.3%, 15.7% and 11.7%) for groups A, B and C respectively, ta king into account values >100 ml min(-1) only. We demonstrated that Tc -99(m)-MAG3 clearance is highly reproducible under the same conditions . However, a repeat clearance measurement on a separate day revealed l arge differences. Therefore, in follow-up studies for evaluation of ch anging kidney function (e.g. surgery or chemotherapy), differences sho uld exceed 30% (i.e. 2 S.D. of group B) to be statistically significan t.