To the Editor: I agree with Jones1 that the body surface area (BSA) formula printed in the position statement on reporting of estimated glomerular filtration rate (eGFR)2 is wrong, even though the authors say that he is mistaken.3

As stated by Jones, the correct formula4 for BSA in m2, for a body weight W kg and height H cm is:

However, the position statement2 gave the following formulas:

It appears that the denominator “1.73” has migrated from formula (iii) to formula (ii), so in fact both of these formulas are incorrect. This is potentially misleading for doctors and others who may want to calculate the eGFR for someone who is unusually big or small.

Formula (iii) should in fact be:

It is interesting that the same two errors in BSA calculations are present on the US National Kidney Disease Education Program website,5 which was presumably the source of the formulas used by the Australian Creatinine Consensus Working Group.

In reply: McNeil draws attention to the detail in the correction factor we published in an attempt to assist users to “uncorrect” the eGFR derived from the MDRD (Modification of Diet in Renal Disease) equation used in calculating GFR from a serum creatinine concentration. Recalculating the eGFR to remove the adjustment for body surface area (BSA) in an individual is unnecessary except at extremes of body size.1

Readers can be reassured that the formulas published in the position statement,2 if used as directed, will not lead to any error. However, it would have been clearer if we had labelled the “BSA” equation as “correction factor” instead of “BSA”. In the position statement2 it can be misinterpreted that the BSA formula has a denominator, whereas, when used primarily to calculate BSA, it of course does not. Both versions of the formulas (ours in the position statement and McNeil’s) therefore lead to identical answers. The reader can choose which one to use.