My gfr for two tests 4 days apart were 62 and 48. these were in different hospitals. i am overweight but exercise quite often. have been under stress?

See below: The glomerular filtration rate is designed to reflect how well your kidneys are functioning. Typically > 60 is considered normal. Each lab is different, so numbers are best compared within the same lab. The GFR is based on creatinine , waste product of muscle, that is filtered/cleared by your kidneys. May not be accurate if you are young, obese, very muscular or pregnant. Discuss with your doc.

Gfr : Gfr variation can be seen depending upon gender, race, muscle mass and age. Also different lab have some variability. If creatinine is also worsened then GFR is reflective of the change, but if creatinine is stable there might be a variability among the labs and checking 24 hr urine for creatinine clearance (equivalent to gfr) will be a better reflection of true GFR in this situation.