The gold standard until the 2006 K/DOQI guidelines were adopted was based on the CANUSA study [7], which clearly showed a difference in mortality between different delivered Kt/V values, a 0.1 unit of Kt/V increase conferring a 5% advantageous RR of survival. Interestingly the CANUSA study had a higher death rate in US patients compared to Canadians, and the former had a higher BSA. Peritoneal Kt/V was 1.5 in Americans and 1.7 in Canadians (the renal Kt/V was not different between the 2 groups). Could the difference in Kt/V explain the different mortality rates? We think so, since there were clear separations at all time points on the Cox proportional hazard survival graphs. Since there were more African-Americans in the American than Canadian patient population (African-America hemodialysis patients have a higher survival rate than white subjects), we are even more convinced that the lower Kt/V in the US patient group was responsible for lower survival. It has been said that we should revisit the middle molecule theory to ex plain the lack of higher Kt/Vurea contributing to survival in the ADEMEX and Hong Kong studies - however, markers of middle molecules were not published in the reports. ^-Microglobulin was associated with increased hospitalization days, as was lower Kt/V, in the CANUSA study lending some credence to the middle molecule hypothesis, but p2-microglobulin is also higher in poorly dialyzed subjects. Reanalysis of the CANUSA data revealed that a 5-liters/week increment in residual glomer-ular filtration rate could explain all the benefits of the increased dialysis dose [8]. However, it does not explain the differences between the 2 countries.

The background mortality in a country's general population is reflected in its dialysis population - a DOPPS

study demonstrated substantial differences in US, European and Japanese mortality dialysis patients (in descending order as reflected in the general populations) [9]. Could the background mortality and body size have any influence on the lack of demonstrated advantage of a higher Kt/V. It is interesting to speculate that it might.

The number of patients being treated with CAPD has fallen in recent years - was this due to the inability to achieve the old DOQI standard, and have the new K/ DOQI guidelines promulgated an achievable standard?

We think that the new K/DOQI guidelines are not applicable to North American populations.

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