Thanks for asking. The E bit refers to it being an estimate from the blood test available rather than the actual. The GFR bit stands for Glomerular Filtration Rate. GFR is a way we measure the functioning of the kidney. The aim would be to have a normal GFR. Certain conditions, cause damage to the glomeruli (the functioning units of the kidney) and cause a decrease in the GFR. The way to prevent a worsening in the GFR depends on what's causing the damage to the kidney. There's a video from Kidney expert Dr Salisbury that explains a bit more: https://health-shared.com/stories/what-is-glomerular-filtration-rate-gfr-0957