How Low can Creatinine Clearance Go, and Yet Life Remains Sustained in Elderly?

We came across a somewhat peculiar case of terminal renal insufficiency in an elderly lady. We believe this case illustrates well the difficulties that a clinician faces on daily basis regarding the evaluation of glomerular filtration rate building on serum Creatinine level measurement alone. We have witnessed a creatinine clearance plunging till less than 2 ml/min without real need for renal replacement therapy. We have performed a Cystatine c serum level measurement for comparison.