To find an improved method of determining renal sufficiency by exploring power functions for estimating normal value, E(arg), single compartment glomerular filtration rate (G 1), rate constant (γ) and renal sufficiency index, RSI=γ/E(γ)=G 1/E(G 1), using compartment volume (V), patient mass ( W), patient age (A), patient height (H), and sex (S). To present the best estimator of normal, E(G 1)=f(V, W).
One hundred and thirty 99mTc-diethylenetriaminepentaacetic acid (99mTc-DTPA) combined imaging and G 1 studies in 97 children were screened by findings and history to obtain 44 normal studies of patients 1.46–18.5 years of age with blood samples at 109 (90–214) and 152 (120–246) min. Normal studies were used to generate predictive formulae.
For power functions,
the statistically acceptable formulae in descending order of adjusted R 2 were f(V, W), f(V,A), f(V,H), f(V), f(W,A,H), f( W), f(H) and f(A). Relationships of the body surface area type, f(W, H, S) and f(W, H), were statistically unwarranted. Kleiber's law, E(G 1)∝∝ W 3/4, with E(G 1)=6.9190W 0.7618 found here, allowed confirmation of GFRinulin≈0.87G 1. The best estimator is f(V, W)=10.998V 0.64717 W 0.20185, and may relate to a volumetric measure of body habitus. To verify methods, Monte Carlo simulation of the glomerular filtration rate (GFR) and f(V, W) was performed and yielded less than 5% precision error, 98% of the time. Normal RSI from f(V, W) had the smallest standard deviation, 11.3%, no regression bias over a six-fold range on a Bland–Altman ratio plot, p=0.4, and good agreement with clinical classification at 95% specificity (RSI>0.8589, Cohen's Kappa 0.70±0.062 (mean±bootstrap standard error).
The best RSI from f(V, W) is RSI=90.927γ V 0.35283 W −0.20185 and should detect mildly (14.1%) reduced renal sufficiency.
aRadiology, Memorial University of Newfoundland, Canada
bDiagnostic Imaging, The Hospital for Sick Children, Toronto, Canada
cCenter for Astrophysics & Space Sciences, University of California, San Diego, USA
Correspondence to Dr Carl A. Wesolowski, Nuclear Medicine, The General Hospital, HSC, 300 Prince Philip Drive, St. John's, NF, Canada, A1B 3V6.
Tel: +001 709 777 6132; fax: +001 709 777 8267;
Received 7 May 2006 Accepted 6 July 2006