To the Editor: The publication of an Australasian position statement on reporting estimated glomerular filtration rates (eGFRs)1 is welcome. It may, however, contain errors and unexplained assumptions.

Firstly, along with its US2 and UK3 counterparts, the position statement recommends the use of the MDRD (Modification of Diet in Renal Disease) four-variable formula to derive eGFR from a patient’s serum creatinine level. Results obtained using this formula are more accurate than those from a patient’s calculated creatinine clearance rate. In accordance with the US guidelines, the Australasian position statement specifies that the total error in laboratories’ serum creatinine measurements should be less than ± 15% if they are to meet overall reporting acceptability. It claims that results that lie within ± 15% of results derived from the reference method procedure (isotope dilution mass spectrometry) also lie within ± 15% of results based on applying the MDRD formula to CX3 analyser readings and thus “fulfil the accuracy criterion”. Australian physicians should be wary of this claim. Assays from which the MDRD formula was derived were reportedly performed on an older analyser than the CX3,4 with possibly even less accurate results. Serum creatinine results produced by a CX3 analyser are themselves about 16% positively biased compared with results calculated by the reference method.5 It is thus possible to be within 15% of a CX3 result and yet, at worst, be > 30% shy of the “true” creatinine value assayed by the reference method. Laboratories should explain to clinician clients the limitations of their creatinine assays.

Secondly, the precision of an assay varies with the level of analyte being analysed — a nuance to be considered, but too technically complex to address further here. The position statement barely touches on this issue.

Thirdly, the position statement opts for 60 mL/min/1.73m2 as the upper limit for reliable reporting of eGFR. It offers reasons why it takes this approach, but does not explain why the chosen level varies from US and UK reporting practices (both choose 90 mL/min/1.73m2 as the cut-off point).

Finally, the UK guidelines sensibly changed the US terminology for racial derivation from “African-American” to “African-Caribbean” when indicating a need to adjust the eGFR reported. The Australasian position statement adopts the term “African-American”. Australian Africans are not African-Americans, nor do all Africans have similar physical stature to people whose ancestors lived in sub-Saharan west and central Africa and who became slaves in the United States or lived in English Caribbean colonies. More care will be needed in reporting here if clinicians are not to be needlessly confused.