Glomerular filtration rate (GFR) is widely accepted as the best index of kidney function in health and disease, and accurate values are required for optimal decision-making. Estimated GFR has been included in clinical practice guidelines to enable physicians to identify patients with chronic kidney disease (CKD) to enable earlier interventions to slow the progression of the disease.1 Measured GFR using urinary or plasma clearance of exogenous filtration markers is considered the gold standard for evaluation of kidney function but is not routinely available. Inulin, creatinine, and urea are candidate markers of GFR. Additionally, a number of radiolabelled chelates have been used to assess GFR. It is recommended that CKD be classified based on the GFR category and the albuminuria category.2