A review of Slope Intercept GFR patient data to validate and optimize the introduction of Single Sample GFR technique

The Glomerular filtration rate (GFR) is a quantitative measure of kidney function determined from the plasma clearance of a radiopharmaceutical such as 51Cr EDTA or 99mTc DTPA. The British Nuclear Medicine Society 2018 guidelines recommend a single sample GFR (SS-GFR) analysis method replacing the slope intercept method (SI-GFR) of the previous 2004 guidelines. This research explores the feasibility and implications of making the transition from SI to SS GFR, by retrospectively determining the SS GFR on a patient population whose GFR was previously evaluated using SI-GFR. One shortcoming of the SS-GFR method is that a prior approximation of the GFR is necessary for choosing a sampling time for an accurate result. The objectives of this study are to, firstly, assess the agreement and associated errors of the SS-GFR when compared to SI GFR and, further, to optimise the single sample approach. The study examines the reliability of using previous GFR measurement or a biochemically determined eGFR documented in the patient healthcare record as a guide to optimum blood sampling time. The use of other GFR predictors is also investigated for patients undergoing DTPA imaging, functional indicators gained from renogram curves such as body surface area (BSA) and sensitivity corrected summed functional phase slopes. Regression analysis will be carried out on renogram parameters to identify the statistically significant predicators (p$<$0.05) which will be entered into a multivariate model. Statistical agreement between the SI-GFR and SS-GFR is tested using Bland-Altman plots and the associated errors quantified.