Abstract
Background: Measurement of glomerular filtration rate from the plasma clearance of a radionuclide labeled tracer is reliable and accurate. However, in order to avoid contamination of the blood samples with radioactivity remaining at the injection site, it requires venepuncture in at least two sites: one for the administration of tracer, and the other/s for blood sampling. This is uncomfortable for patients particularly when venous access is difficult. The objective of this study was to validate the use of a single site of venous access in combination with injection site imaging, for glomerular filtration rate measurement. Methods: Twenty-two adults(≥ 18 years), who were referred for GFR determination were included prospectively. GFR was measured from the plasma clearance of 99mTc- diethylenetriaminepentaacetic acid (99mTc-DTPA) according to international guidelines. After administration of the tracer through an intravenous (IV) cannula, a 60-second static image of the injection site was acquired. A second IV cannula was inserted into the contralateral arm. Venous blood samples were collected at 2, 3 and 4 hours after the administration of the radiotracer from both the injection site (experimental) and contralateral limb (conventional). GFR was calculated using slope-intercept (SI-GFR) and single sample methods (SS-GFR). The median conventional and experimental plasma counts (decay and background-corrected) were compared for the 2, 3 and 4 h venous samples. Conventional GFRs (GFRcon) and experimental GFRs (GFRexp) were then compared, with a > 10% difference between GFRexp and GFRcon being regarded as significant. Results: Four individuals had visible residual activity at the injection site. The median 2 h counts at conventional and experimental sampling sites were significantly different (P = 0.007), whereas no significant difference was found at 3 h and 4 h. In cases with a clear injection site image, for SS-GFR the difference between GFRexp and GFRcon was > 10% in 1 case, whereas for SI-GFR all differences were < 8%. Conclusion: In cases with clear injection site images, SI-GFR calculated after injection site blood sampling showed no clinically significant difference to conventional contralateral limb sampling.