Introduction: There are several shortcut formulas to calculate Kt/V, the most widely used because of its simplicity is the logarithmic formula proposed by Lowrie in 1983. The DOQI report recommends use of the formula proposed by Daugirdas's in 1993 to estimate the Kt/V, it must be > or = 1.2. The aim of the present work was to analyse the concordance between the second generation Daugirdas's formula and the other shortcut formulas.
Material and methods: In 208 hemodialysis sessions performed on 61 patients, Kt/V was estimated by thirteen formulas: 10 single-pool modeling and three double-pool modeling.
Results: The Kt/V values obtained by Daugirdas's formula was different from those obtained with the other single-pool based formulas (p < 0.01). When the dialysis sessions were classified in 4 groups according to the Kt/V values calculated by Daugirdas's formula, most of the single-pool formulas gave Kt/V values statistically different from those given by Daugirda's formula in all ranges examined. The concordance among Kt/V calculated by every one of the single-pool formulas and Daugirdas's formula was variable. The highest agreement was with Keshaviah's and Lowrie's 1992 formulas and the lowest with Calzavare's and Lowrie's 1983 formulas. The linear multivariate analysis showed that the two factors which influenced the concordance were the Kt/V value obtained by the Daugirdas's formula, and the quotient between the postdialysis body weight and the ultrafiltration rate. Despite the weak concordance with Daugirdas's formula, the Kt/V obtained by Lowrie's 1983 formula and the urea reduction ratio (URR) are still useful tools to monitor the adequacy of dialysis: a Kt/V > 1.065 calculated by the Lowrie's 1983 formula and a PRV > 65% are equivalent to a Kt/V > or = 1.2 calculated by Daugirdas's formula.
Conclusions: The shortcut formulas used to calculate Kt/V give different results with high inter-method variability. When Kt/V is reported it is absolutely necessary to indicate the formula used to calculate it. The Kt/V obtained by Lowrie's 1983 formula and the URR are useful tools to monitor dialysis adequacy.