Glomerular filtration rate (GFR) is usually estimated rather than measured as this only requires measurement of an endogenous filtration marker. In certain clinical settings a more accurate measure of GFR is essential. The most commonly used endogenous filtration marker is creatinine. Exogenous filtration markers include nonradiopharmaceuticals such as inulin, iohexol and unlabelled iothalamate, or radiopharmaceuticals such as 51Crethylenediaminetetraacetic acid (51Cr-EDTA) and 99mTc-diethylenetriaminepentaacetic acid (99mTc-DTPA). Inulin is considered an ideal filtration marker but the clearance of iothalamate, 99mTc-DTPA, 51Cr-EDTA and iohexol have all been shown to have sufficient accuracy for measuring GFR. For radiopharmaceuticals, a well counter is required to measure the amount of activity in patient samples. Iohexol or unlabelled iothalamate require samples to be measured using high performance liquid chromatography with ultraviolet detection (HPLC-UV), liquid chromatography-tandem mass spectrometry (LC-MS/MS) or x-ray fluorescence (XRF). Due to the practical challenges of measuring urinary clearance, measurement of GFR in clinical settings is almost exclusively based on plasma clearance of a filtration marker. This can follow a long-established approach based on the ratio of the tracer administered to the area under the plasma concentration curve. Alternatively, a single plasma sample giving an apparent volume of distribution at a given time point can be used to accurately measure GFR. While techniques exist for the measurement of GFR in a number of African countries, preliminary evidence suggests that facilities are very limited. There is a need for support for both equipment and training to establish GFR measurement facilities in several centres on the continent. Keywords: measured glomerular filtration rate;, mGFR;, Africa

Background The goal of post-diagnosis diabetes management is the achievement and maintenance of glycaemic control. Most clinical practice guidelines recommend 3–6 monthly HbA1c monitoring. Despite this guidance, there are few data supporting the impact of monitoring frequency on clinical outcomes, particularly from low- and middle-income country settings. This study examined associations between adherence to monitoring recommendations and the achievement of HbA1c targets, and HbA1c changes, over time in a South African cohort. Research Design and Methods: The study utilised routinely collected HbA1c test data on patients with diabetes aged ≥ 18 years in the Western and Northern Cape between 2015 and 2020 to examine the relationship between mean change in HbA1c values and the duration between consecutive HbA1c tests (retest interval). The monitoring adherence rate, which represents the proportion of intervals between consecutive tests that met South Africa’s guideline recommendations, was calculated for each patient. Multistate modelling and linear mixed-effects modelling were then used to examine the effect of monitoring adherence on the achievement of glycemic control targets and longitudinal changes in HbA1c. Results The 132,859 diabetes patients with repeat tests had a median of three HbA1c test requests, a median follow-up time of 2.3 years and a median retest interval of 10.3 months. A retest interval 2–4 months maximised the downward trajectory in HbA1c, while individuals with low adherence to the monitoring guidelines were the least likely to achieve glycaemic control in one year. Moreover, patients with low monitoring adherence had higher mean HbA1c levels compared to patients with moderate or high monitoring adherence. Conclusions The results illustrated the importance of adherence to monitoring recommendations as adherent patients had better glycaemic control and lower mean HbA1c levels over time.