Age-specific normal reference ranges for ^99mTc-DTPA glomerular filtration rate to use with two-sample slope-intercept method and Jodal Brochner-Mortensen correction

Glomerular filtration rate (GFR) varies with age, the calculation method, and the correction factor for slope-intercept overestimation. Hence, any normal reference range accompanying the results should be suitably adapted to the method used. For Nuclear Medicine Departments using a two-sample slope-intercept method, the lack of appropriate age-specific normal reference range has been a hindrance to adopting the recently updated Jodal Brochner-Mortensen (JBM) correction over other older and more widely used methods. A retrospective analysis of the routine GFR calculation and clinical reports generated locally from 2006 to 2020 was carried out. GFR was calculated with ^99mTc-DTPA plasma clearance using a two-sample slope-intercept method with JBM correction. Age-specific normal range equations were developed from normal healthy subjects. Published normal reference ranges were modified with appropriate correction reversal and compared with the locally developed reference ranges. Age-specific normal GFR reference ranges for ^99mTc-DTPA with slope-intercept method and JBM correction were developed and validated with current literature. Normal reference range (Mean ± 2SD) for Normalised GFR (ml min^-1 (1.73m²)^-1) within 95% confidence limits suitable for use with JBM correction is 100.6 ± 35.2 for children above 2 years and 102.9 - 0.00629 × (Age)² ± 19.4 for adults. Availability of age-specific normal GFR reference ranges applicable to the target population and appropriately tailored to the calculation method and correction factor enables Nuclear Medicine Departments to update their calculation methods in line with the current literature and also facilitates accurate reporting and evaluation of the calculated GFR results.