Chromium-51-EDTA clearance in adults with a single-plasma sample

• In 1996, a committee on renal clearance recommended a mean sojourn time-based methodology for single-sample determination of plasma clearance of 99mTc-diethylenetriamine pentaacetic acid (DTPA) to be used on adults if the patient's glomerular filtration rate (GFR) is suspected to be >30 ml/min. The main purpose of this study was to derive a mean sojourn time-based formula for calculation of 51Cr-ethylenediamine tetraacetic acid (EDTA) clearance in adults. Methods: Two groups of patients with 51Cr-EDTA clearance (CI) between 16 and 172 ml/min were studied. In Group I (n = 46), reference CI was determined as a multi plasma sample, single-injection method (CISM). Sixteen blood samples were drawn from 0 until 5 hr after a single intravenous injection of 51Cr-EDTA. In Group II (n = 1046), reference CI was determined by the Brøchner-Mortensen four-sample clearance method (CIBM). The plasma timeactivity curves of Group I were used to derive two mean sojourn time-based formulas (Formulas 1 and 2) for calculation of a single sample clearance. Formula 1 was derived from the entire time activity curve, whereas the derivation of Formula 2 used only the final slope of the time-activity curve. The accuracy of the two formulas and the Christensen and Groth 99mTc-DTPA formula was tested on Group II. Results: Chromium-51-EDTA CI calculated by Formula 1 was almost identical to the CI calculated by the reference CI method (r = 0.982; SDdiff = 5.82 ml/min). Both 51Cr-EDTA CI calculated by Formula 2 and by the 99mTc-DTPA formula showed close correlation with the reference method (r = 0.976, r = 0.985, respectively) but systematically overestimated GFR for the whole range of clearance values by 3.5 and 3.2 ml/min (p < 0.001), respectively. Conclusion: It is possible to get an accurate determi nation of 51Cr-EDTA CI from a single-plasma sample in adults by the mean sojourn time methodology. The determination is marginally more accurate (p < 0.001) if using a formula derived from the entire plasma time-activity curve than from only the final slope. The single-sample formula derived for determination of 99mTc-DTPA CI tends slightly to overestimate GFR if used to calculate 51Cr-EDTA CI.

Nyckelord

single sample

chromium-51-ethylenediaminetetraacetic acid clearance

glomerular filtration rate

renal function

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