RESUMO
AIM: To correlate between the radionuclide in vitro plasma sampling method (using single and dual blood samples) and Gates' GFR measurement using Tc-99m diethylene triamine penta-acetic acid (Tc-99m DTPA) renal scintigraphy (in vivo method). METHODS: This study included 40 renal donors (group 1) and 40 patients with obstructive uropathy (group 2). Group 1 included 22 males and 18 females with an age range from 22 to 65 years, while group 2 included 24 males and 16 females with age range 27 to 64 years. Both groups subjected to renal Scintigraphy after administration of 5 mCi 99m-Tc DTPA, GFR was calculated using Gates' method (in vivo method), then plasma sampling was acquired at 60 mins and 180 mins post-injection of the tracer, samples were counted in well counter and GFR was calculated using in vitro technique either using single plasma sample (SPSM 60 mins) or dual sample (DPSM 60 & 180 min). Additionally, GFR was measured by estimated equations based on serum creatinine. RESULTS: In group 1, the mean GFR using in vivo Gates' method was 115.7 ± 29 ml/min, while using the SPSM was 100.1 ± 16.1 ml/min, and the DPSM was 100.3 ± 20.1 ml/min. In group 2, mean GFR using in vivo method was 74.1 ± 14.5 ml/min, while using in vitro SPSM it was 77.5 ± 24.9 ml/min and DPSM was 76.8 ± 24.8 ml/min. There was no significant difference between mean GFR values using in vivo and in vitro methods (single or dual samples) in group 1 and 2 (p > 0.05). There is high significant correlation between SPSM and DPSM in groups 1 and 2 (r = 0.90, r = 0.91 respectively), moderate significant correlation was found between in vivo Gates' method and in vitro SPSM in group 1 and 2 (r = 0.46 and 0.57 respectively) and moderate correlation was evident between in vivo and in vitro DPSM in both groups (r = 0.42 and 0.68 respectively). By using the DPSM as the reference standard significant high correlation was found with SPSM and significant-high moderate correlation with in vivo Gates' scintigraphic method. Conclusion: In vitro plasma sampling considered as a reliable, accurate |method for GFR calculation yet it considered relatively complex, both single and dual sample in vitro techniques showed a very high correlation, and hence SPSM can replace DPSM. CONCLUSION: Renal scintigraphy and GFR estimation using Gates' in vivo method is considered inaccurate, yet given its simplicity in performance it can still be used if corrected GFR is standardised for Egyptian population-based on studies with large numbers of patients from multiple centres.
RESUMO
BACKGROUND: There are numerous methods for calculation of glomerular filtration rate (GFR), which is a crucial measurement to identify patients with renal disease. AIMS: The aim of this study is to compare four different methods of GFR calculation. SETTINGS AND DESIGN: Clinical setup, prospective study. MATERIALS AND METHODS: Data was collected from routine renal scans done for voluntary kidney donors (VKD) or renal transplant recipients 6 months after transplantation. Following technetium-99m diethylene triamine penta acetic acid injection, venous blood samples were collected from contralateral arm at 120, 180, and 240 min through an indwelling venous cannula and direct collection by syringe. A total volume of 1 ml of plasma from each sample and standards were counted in an automatic gamma counter for 1 min. Blood samples taken at 120 min and 240 min were used for double plasma sample method (DPSM) and a sample taken at 180 min for single plasma sample method (SPSM). Russell's formulae for SPSM and DPSM were used for GFR estimation. Gates' method GFR was calculated by vendor provided software. Correlation analysis was performed using Pearson's correlation test. RESULTS: SPSM correlated well with DPSM. GFR value in healthy potential kidney donors has a significant role in the selection of donors. The mean GFR ± (standard deviation) in VKD using SPSM, DPSM, camera depth method and Cockroft Gault method was 134.6 (25.9), 137.5 (42.4), 98.6 (15.9), 83.5 (21.1) respectively. Gates' GFR calculation did not correlate well with plasma sampling method. CONCLUSIONS: Calculation of GFR plays a vital role in the management of renal patients, hence it was noted that Gates GFR may not be a reliable method of calculation. SPSM was more reliable. DPSM is reliable but cumbersome. It is difficult to accurately calculate GFR without a gold standard.