I am not sure what type of radioisotope renal scan did you undergo but they are highly operator dependent. The results may vary from centre to centre, and are dependant on the person reading and interpreting these scans. Therefore, their utility as a measure of GFR is at best can be described as variable and less reliable than various other measures available. No, anxiety will not lower or alter the results of these scans. Urine protein and ultrasound generally may indicate the nature and presence of renal disease but never allow you to measure GFR (or kidney function). And, a normal renal ultrasound or absence of urine protein do not necessarily rule out any kidney disease.