Using the slope-only technique and estimated glomerular filtration rate for checking the reliability of slope-intercept measurement of glomerular filtration rate

Aim To develop a strategy for checking the reliability of slope intercept measurement of glomerular filtration rate (GFR). Methods Six blood samples, obtained bilaterally 20-240 min after the injection of Cr-51-ethylenediaminetetraacetic acid (EDTA) and iohexol into opposite arms, were assayed for indicator injected contralaterally. GFR6(iohexol), the reference value, was measured for all six samples and GFR3(EDTA) (slope-intercept) for the last three samples (per 1.73 m(2)). GFR was measured from the half-time [GFR/extracellular fluid volume (ECV)3(EDTA)], for the single samples at 2-4h (Christensen-Groth; GFR1) and for creatinine [estimated GFR (eGFR)]. Results In six of the 97 studies, the correlation coefficient W of the fit to the last three sample points was less than 0.99. In the remaining 91 studies, GFR3(EDTA) disagreed with GFR/ECVEDTA by more than 15% in 19 studies (group A) and by less than 15% in 72 studies (group 13). GFR3(EDTA) disagreed with GFR6(iohexol) by 12.6% in group A but only by 6.3% in group B (P < 0.001). No such discrimination was displayed by eGFR. Although GFR3(EDTA) was within 15% of GFR6(iohexol) in 14 group A studies, eGFR was within 15% of GFR3(EDTA) in only eight studies and disagreed by more than 15% in six studies. Conversely, in the five of the 19 studies in which GFR3(EDTA) disagreed with GFR6(iohexol) by more than 15%, the agreement between eGFR and GFR3(EDTA) Was less than 15% in two studies and more than 15% in three studies. GFR3(EDTA) was within 15% of GFR/ECV3(EDTA) in all six studies in which r was less than 0.99, and GFR3(EDTA) disagreed with GFR6(iohexol) by less than 15%. Confidence in GFR3(EDTA) was not improved by GFR1 or eGFR. Conclusion Slope intercept GFR is reliable if within 15% of GFR/ECV3. Estimated GFR was ineffective as a second checkpoint. GFR1 did not help when the fit was poor. Nucl Med Commun 29:1086-1092 (c) 2008 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.