Accurate and precise plasma clearance measurement using four 99mTc-DTPA plasma samples over 4 h
Surajith N Wanasundara1, Michal J Wesolowski, Mark C Barnfield
1aDepartment of Medical Imaging, Royal University Hospital, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan bDepartment of Radiology, Memorial University of Newfoundland, Nuclear Medicine, The General Hospital, St. John's, Newfoundland and Labrador, Canada cThe Department of Medical Physics and Engineering, St. James's University Hospital, Leeds dNuclear Medicine Department, Sheffield Teaching Hospital NHS Foundation Trust, Sheffield eNuclear Medicine Department, The Royal Free London NHS Foundation Trust, London, UK.
Objectives:
Glomerular filtration rate can be measured as the plasma clearance (CL) of a glomerular filtration rate marker despite body fluid disturbances using numerous, prolonged time samples. We desire a simplified technique without compromised accuracy and precision.
Materials And Methods:
We compared CL values derived from two plasma concentration curve area methods - (a) biexponential fitting [CL (E2)] and (b) Tikhonov adaptively regularized gamma variate fitting [CL (Tk-GV)] - for 4 versus 8 h time samplings from 412 Tc-DTPA studies in 142 patients, mostly paediatric patients, with suspected fluid disturbances.
Results:
CL (Tk-GV) from four samples/4 h and from nine samples/8 h, both accurately and precisely agreed with the standard, which was taken to be nine samples/8 h CL from (noncompartmental) numerical integration [CL (NI)]. The E2 method, four samples/4 h, and nine samples/8 h median CL values significantly overestimated the CL (NI) values by 4.9 and 3.8%, respectively.
Conclusion:
Compared with the standard, CL (E2) from four samples/4 h and from nine samples/8 h proved to be the most inaccurate and imprecise method examined, and can be replaced by better methods for calculating CL. The CL (Tk-GV) can be used to reduce sampling time in half from 8 to 4 h and from nine to four samples for a precise and accurate, yet more easily tolerated and simplified test.
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