Established chronic kidney disease (CKD) requires treatment with dialysis or transplantation, both of which are expensive. In addition, the late referral of patients requiring renal replacement therapy can have negative effects.^1–4 As a result, it is recommended that estimated glomerular filtration rate (eGFR) using the Modification of Diet in Renal Disease (MDRD) equation be used to identify people with CKD and those at risk of end-stage CKD.^5–7 However, MDRD-derived eGFRs are reportedly less precise above 60 ml/min/1.73 m² when a kinetic alkaline picrate assay is used.⁸

We derived eGFR using the four-variable MDRD equation in 100 patients undergoing the creatinine clearance test (CCT) as assessed by 24 h urine collections using a kinetic alkaline picrate assay (Olympus Life and Material Science Europe (Irish Branch) Lismeehan, O’Callaghan’s Mills, Ireland).

GFR (ml/min/1.73 m²) = 186×((serum creatinine (μmol/l)/88.4)^−1.154)× age (years)×0.742 if female and ×1.21 if African American.

Urinary protein was requested for 85 patients and was measured using pyrogallol red-molybdate (Olympus Diagnostica). Absolute and relative difference plots were drawn (fig 1) and the median bias was calculated for all stages of CKD. For each level of proteinuria, the median percentage difference was calculated (table 1).