Longitudinal assessment of glomerular filtration rate by gamma camera and portable external detector

Noninvasive isotope chelate methods to assess glomerular filtration rate (GFR) are less accurate than blood sampling. However, some measurement errors would be expected to be constant for an individual, and repeat estimations may be less variable. In 18 patients, estimates of GFR were obtained by 2 gamma camera techniques and a portable external detector at a mean interval of 1 year, to assess accuracy in predicting a change of GFR. Errors in these techniques were not significantly better than those predicted from two independent estimates. Most GFR measurement error for noninvasive methods appears to be random.