Lean body mass to estimate GFR.

Sir, The interesting paper by Taylor et al. [1] lends support to the idea that the variables used in the different formulas to estimate GFR (glomerular filtration rate) are surrogate markers of lean body mass. The following letter by Rigalleau et al. [2] did not fully confirm the findings, at least in diabetic patients. We are rather puzzled by a part of the analysis conducted in the Taylor’s paper however, i.e. it is not clear to us whether the GFR estimated by the new formula (including lean mass) and by the Cockcroft and Gault formula have been normalized in relation to body surface area. We feel that this is an important issue to consider for a proper comparison with measured GFR and the modification of diet in renal disease (MDRD) formulae, which express GFR values as ml/min/ 1.73m. It is also not clear why the authors did not match their data against the original, 6-variable MDRD formula. It would be interesting to know whether Taylor’s results afford an improvement over the GFR measured or estimated by the Cockcroft and Gault formula, all after normalizing for body surface area, or the classical MDRD calculation.