No abstract

Chronic kidney disease (CKD) is defined by the presence of abnormalities of kidney structure or function (such as a glomerular filtration rate (GFR) <60 mL/min/1.73 m 2), present for >3 months, with implications for health. [1] The Kidney Disease: Improving Global Outcomes (KDIGO) guideline recommends using a creatinine-based equation to estimate GFR in the initial assessment of CKD and for monitoring disease progression. [1] The two most commonly used equations in adults are the Modification of Diet in Renal Disease (MDRD) equation [2,3] and the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation. [4] Unless an alternative equation has been shown to have superior accuracy, use of the CKD-EPI equation is recommended. [1,5] A 2012 systematic review found that neither the MDRD nor the CKD-EPI equation performed well in populations outside North America, Europe or Australia, and it concluded that neither equation could be used routinely across all populations and all GFR ranges. [6] Studies conducted in various South African (SA) populations support this, and although the findings varied, the equations tended to have unacceptable bias, precision and/or accuracy. [7-11] The poor performance of the equations in SA populations is concerning. SA is a developing country with limited centres that are able to measure GFR. Even where the service is available, the large number of CKD patients attending renal clinics precludes routine GFR measurement, compelling physicians to rely on estimated GFR (eGFR). Furthermore, GFR estimates are essential in epidemiological studies, specifically to determine CKD prevalence. The mixed-ancestry (coloured) population group is estimated to comprise 8.8% of SA's population [12] and almost 49% of the Western Cape Province population. [13] Its origins are Khoisan (32-43%), Bantu-speaking African (20-36%), European (21-28%) and Asian (9-11%). [14] No previous studies have evaluated GFR-estimating equations in this group, despite the fact that it has a high prevalence of CKD. [15,16] Considering the population group's genetic diversity, it is hypothesised that accuracy of the commonly used equations will be poor.

Well-defined reference data for VD and T1/2 can be used for quality control checks in GFR investigations. In addition to these, reference data for GFR using Tc-DTPA have been defined. This will enhance the interpretation of adult Tc-DTPA GFR measurements.