To the Editor: We were pleased to read the position statement of the Australasian Creatinine Consensus Working Group1 recommending that laboratories automatically report estimated glomerular filtration rate (eGFR) each time a serum creatinine test is ordered in adults. We implemented this at Christchurch Hospital in March 2005 after consultation with key clinical staff. It has been well received and has resulted in a significant fall in the ordering of 24-hour urine collections.

We firstly validated the performance of the abbreviated MDRD (Modification of Diet in Renal Disease) equation2 in a pilot study of 30 patients aged 40–85 years in a steady state undergoing radionuclide GFR measurement, adjusted for body surface area. The MDRD calculation showed a mean bias of –4.2 mL/min/1.73m2 (95% CI, –12.9 to 4.5 mL/min/1.73m2) compared with –7.1 mL/min/1.73m2 (95% CI, –18.5 to 4.2 mL/min/1.73m2) for the Cockcroft–Gault equation — thus, less bias and dispersion.

The position statement advocates measuring serum creatinine concentration to the nearest 1 mmol/L to avoid premature rounding of data in the calculation. However, other studies have suggested that this is inappropriately tight,3 and we contend that, although this is an appropriate manipulation in the calculation, it does not need to be preserved at the point of reporting, when a creatinine concentration to the nearest 10 mmol/L would be sufficient.

At our hospital, “adult” status begins from the age of 16 years, and clinicians expressed a preference that we report eGFR from this younger age. They also expressed a preference that we report actual values rather than “> 60 mL/min/1.73m2”. Given the absence of well validated age-adjusted normative data, we elected to give a reference range of 80–120 mL/min/1.73m2, while appending the comment, “GFR declines by 1 mL/min/1.73m2 per year over the age of 40 years”. Also included in a comment with every report is the caveat that eGFR is only valid under steady-state conditions and that it has not been validated for extremes of body mass or in pregnant women, non-white populations, oedematous patients or people with other complex conditions.

If the creatinine concentration exceeds an earlier value within the previous 4 days by more than + 17% (a critical difference with 95% probability4), then an alternative comment is issued indicating that steady-state conditions are not met, although eGFR is still reported. Similar considerations regarding non-steady state apply equally to serum creatinine alone.

The position statement is helpful, but should not be regarded as rigidly prescriptive. Institutions should have the freedom to tailor the package to their own requirements, based on consultation with key clinicians.