FRACTIONAL UREA CLEARANCE ESTIMATES USING 2 ANTHROPOMETRIC FORMULAS IN CONTINUOUS PERITONEAL-DIALYSIS - SEX, HEIGHT, AND BODY-COMPOSITION DIFFERENCES

Objective: To compare estimates of urea volume (V) and KT/V obtained b y the Watson and Hume anthropometric formulas, and to identify the sim ilarities and differences between these estimates. Design: Theoretical analysis applying wide variations in the determinants of anthropometr ic V (age, height, weight) in hypothetical women and men. Analysis of urea kinetic studies performed in patients on continuous peritoneal di alysis (CPD). Setting: Four dialysis units in Albuquerque, two in Athe ns, and two in Thessaloniki. Participants: Three hundred and two CPD p atients who had 440 urea kinetic studies. Intervention: Standard urea clearance was performed by 24-hour collections of urine and drained di alysate followed by blood sampling. V was estimated by both the Watson and Hume formulas. Main Outcome Measures: Estimates of V and KT/V wer e compared separately in women and men by Student's t-test, linear reg ression, and limits of agreement (mean difference+/-2 SD). The agreeme nt of the KT/V estimates was also tested by the kappa ratio using a va lue of 1.70 weekly as the lowest acceptable KT/V. Results: The theoret ical analysis indicated important disagreement only in extreme variati ons from the ordinary in height and, to a lesser extent, weight. Diffe rences due to height variation were pronounced only in hypothetical wo men, CPD patient findings were as follows: in women, Watson V and week ly KT/V were 30.4+/-4.4 L and 2.10+/-0.61, respectively. Corresponding Hume estimates were 30.3+/-5.4 L and 2.12+/-0.66, respectively. Corre sponding estimates for men were 40.5+/-5.7 L and 1.92+/-0.57 (Watson) plus 41.4+/-5.6 L and 1.88+/-0.57 (Hume), respectively. By linear regr ession, KT/V-Hume = -0.083 + 1.052 (KT/V-Watson), r = 0.961 (women); a nd KT/V-Hume = -0.026 + 0.992 (KT/V-Watson), r = 0.985 (men). Limits o f agreement were -1.41 L and 2.10 L for V, and -0.15 and 0.14 weekly f or KT/V. In 94.3% of the cases, KT/V-Watson and KT/V-Hume agreed (both >1.70 or both <1.70 weekly). Kappa ratio was 0.875 (excellent agreeme nt). The concordant and discordant groups differed in height and degre e of obesity, in agreement with the theoretical analysis. Conclusion: The Watson and Hume formulas provide similar estimates of V and KT/V i n CPD patients. Differences may be noted only if women's height or, to a lesser extent, both sexes' weight is at a great variance with the o rdinary values.