Variability of estimated glomerular filtration rate and 99mTc-DTPA glomerular filtration rate: implications for a single time-point sampling regime.

BACKGROUND: This work aimed to determine the implications of the variability in estimated glomerular filtration rate (eGFR) for the prediction of measured GFR (mGFR) for selection of sampling time-point in single-sample 99mTc-diethylene-triamine-pentaacetate (DTPA) mGFR.

METHODS: Patient studies were used to compare eGFR and mGFR (n = 282). The eGFR was calculated using the Chronic Kidney Disease Epidemiology Collaboration 2009 equation, from serum creatinine values measured in the laboratory (n = 27) or using a point-of-care testing device (n = 255). The mGFR was taken as the true value, and the root mean square error (RMSerr) in eGFR was calculated. Receiver operator characteristic curves were generated comparing the sensitivity and specificity of eGFR for the prediction of mGFR within the British Nuclear Medicine Society (BNMS) 2018 guideline ranges.

RESULTS: The overall eGFR RMSerr was 19.3 mL/min/1.73 m2. Use of eGFR to predict mGFR in the ranges specified in the BNMS 2018 guidelines (25-50; 50-70; 70-100; and >100) achieved the following specificity and sensitivity for each individual range (97%, 71%; 92%, 47%; 81%, 48%; and 74%, 90%). For the middle ranges (50-70 and 70-100) the sensitivity is very low, less than 50%; more studies are classified incorrectly on the basis of eGFR in these ranges than correctly.

CONCLUSION: This work shows that serum creatinine eGFR is not sufficiently accurate to predict the optimum single-sample time-point for 99mTc-DTPA mGFR prior to measurement. It is the recommendation of this study that a single sampling time-point should be chosen for studies eGFR > 40 ml/min/1.73 m2 as opposed to the use of eGFR to determine the sampling time-point.