Objective: To compare between Gates GFR measurement using 99m Tc DTPA scintigraphy (in vivo method) as compared to in vitro blood sampling method (single and dual blood samples).Patients and methods: this prospective study included 40 normal individuals (group 1) and 40 patients with obstructive uropathy (group2) .The age of the group 1 ranging from: 22 to 65with mean age of 47.1±14.08 and in group 2it ranges between 27 years to 64 years with mean age of 49.12±9.1 .Group 1 included: 22 males, 18females, while group 2 included 24 males and 16 females. Both groups subjected to 99m-Tc DTPA renal scan using 8 mCi followed by blood sampling at 60 mins and 180mins post injection. Serum creatinine level was estimated for both groups and it was within normal level. Results: In group 1, the mean GFR using in vivo method was115.7 ± 29, and using in vitro method with single blood sample it was 100.1 ±16.1, and using dual blood sampling method it was 100.3±20.1.There was no significant difference between in vivo and in vitro methods (single sample and dual samples) for measuring GFR, in group 1 (p>0.05). In group 2, GFR using in vivo method was 74.1 ± 14.5, while using in vitro single sample method it was 77.5 ±24.9, and by using in vitro dual sample it was 76.8 ±24.8 with no significant difference using in vitro single sample and dual sample measurements. There is high significant correlation between in vitro single and dual sample in both groups,(r=0.90) for control group and (r=0.91) for patients group, while moderate significant correlation was found between in vivo and in vitro radionuclide single sample methods in both control and patients groups (r=0.46 and 0.57). Also moderate correlation was evident between in vivo and in vitro radionuclide dual sample methods in both groups (r=0.42 and
0.68).
Conclusion: No significant difference in measurement of GFR using both in vitro and in vivo methods in control group and in obstructive uropathy group ,however there is moderate correlation between in vivo and in vitro (single and dual sample) method in both groups but there is high correlation between in vitro method using single blood sample and dual blood samples.