Mouse to elephant: biological scaling and Kt/V

Am J Kidney Dis. 2000 Feb;35(2):306-9. doi: 10.1016/s0272-6386(00)70341-6.


The construct Kt/V is used by the nephrology community in prescribing dialysis dose. The concerns that have been raised as to what value of V to use in the calculation of Kt/V touch on the more central question of whether filtration rate should be normalized by a parameter other than V. Within the animal kingdom, a number of physiological variables scale to body size according to an equation of the form Y = YoMb, where Yo is a constant, M is body mass, and b is a scaling exponent. Glomerular filtration rate (GFR) in mammals weighing from 30 g to 503 kg scales to body weight with an exponent of 0.77. Hence, GFR per unit body weight (or Kt/V) decreases significantly with increasing body size. Metabolic rate also scales to body size in a wide range of mammals according to the same general equation and with a scaling exponent of 0.75. Because GFR and metabolic rate scale to body mass with virtually the same exponent, a ratio of the two yields a constant independent of body size. We propose that the ratio (filtration rate/metabolic rate) replace Kt/V. Such a ratio would underscore the linkage between filtration rate (and dialysis therapy) and the metabolic demands of the body.

MeSH terms

  • Animals
  • Body Weight*
  • Elephants
  • Glomerular Filtration Rate*
  • Humans
  • Mammals
  • Mice
  • Renal Dialysis / statistics & numerical data*
  • Urea / metabolism*


  • Urea