An improved method for determining renal sufficiency using volume of distribution and weight from bolus 99mTc-DTPA, two blood sample, paediatric data.

OBJECTIVES

To find an improved method of determining renal sufficiency by exploring power functions for estimating normal value, E(arg), single compartment glomerular filtration rate (G1), rate constant (gamma) and renal sufficiency index, RSI = gamma/E(gamma) = G1/E(G1), using compartment volume (V), patient mass ( W), patient age (A), patient height (H), and sex (S). To present the best estimator of normal, E(G1) = f(V, W).

METHODS

One hundred and thirty 99mTc-diethylenetriaminepentaacetic acid (99mTc-DTPA) combined imaging and G1 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.

RESULTS

For power functions, [equation: see text] the statistically acceptable formulae in descending order of adjusted R2 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(G1) proportional to W(3/4), with E(G1) = 6.9190W(0.7618) found here, allowed confirmation of GFRinulin approximately 0.87G1. 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).

CONCLUSIONS

The best RSI from f(V, W) is RSI = 90.927gammaV(0.35283)W(-0.20185) and should detect mildly (14.1%) reduced renal sufficiency.