HDCN Article Review/Hyperlink

Gotch FA, Levin NW, Port FK, Wolfe RA, Uehlinger DE

Clinical outcome relative to the dose of dialysis is not what you think: the fallacy of the mean

Am J Kidney Dis (Jul) 30:1-15 1997

Urea kinetic papers are not usually very clear, so I'll summarize this one in a nutshell. Suppose that mortality at Kt/V at 0.8 is way higher than at 1.0, but then is completely level beyond 1.2. Now suppose the mean Kt/V in your unit is 1.0, and you bring everyone up to 1.5. You see a decrease in mortality. You publish a paper, saying that a Kt/V of 1.2 is not good dialysis; you must keep people at 1.5.

This is the fallacy of the mean. When the mean Kt/V in your unit is 1.0, you have a substantial number of patients on the Bell curve getting Kt/V's of 0.8 and less. When you drive everyone up to 1.5, then the number of people sitting on the lower part of the Bell Curve is the same, but now these people are up around 1.1-1.3, and not at 0.6 to 0.8.

In fact, this is what happened. Parker and Hakim published such a paper, noting a decrease in mortality when they increased Kt/V in around this range. Gotch argues that this does not mean a Kt/V > 1.2 (and we're talking single-pool, here), means lower mortality. He elegantly goes through a number of studies showing why decreased mortality at high mean Kt/V levels can be explained even if the mortality curve is flat beyond 1.2- 1.3 single-pool Kt/V units. (John T. Daugirdas, M.D., University of Illinois at Chicago)

The abstract of this paper is available from the AJKD online at this site.