What is the cause of a low gfr and high anion level?

Renal Insufficiency,: There are several reasons for these values, but the predominant theme of just about all of them is renal insufficiency or failure. Gfr or glomerular filtration rate is lowered, as in toxicity, acute and chronic glomerulonephritis, pyelonephritis, diabetes, dehydration, esrd (end stage renal disease), and atherosclerosis. Many of these, like diabetes & toxicities also cause high anion gap.