Measurement of glomerular filtration rate with technetium-99m DTPA: comparison of plasma clearance techniques.

We have compared several techniques for measuring [99mTc]DTPA plasma clearance following single injection to estimate glomerular filtration rate (GFR). Half hourly measurements of disappearance of plasma activity were used to calculate a reference GFR corrected for one-pool assumption and body surface area. Alternative methods involving (i) single blood sample, (ii) two blood samples, (iii) external detector clearance rate, and (iv) a combination of (i) and (iii) were then compared. Closest correlations were obtained with (i) two blood samples at 2 hr and 4 hr (s.e.e. 2.8 ml/min) and (i.v.) external rate constant from 2-5 hr with a blood sample at 3 hr (s.e.e. 3.0 ml/min). Correlations with single blood sample were closest at 3 hr and 4 hr postinjection (s.e.e. 5.4 and 4.5 ml/min, respectively). External detector disappearance rate constant alone was least accurate (s.e.e. greater than 10 ml. min).