Creatinine fluctuates between 1.05 & 1.35. bun between 10 & 18. cystatin- c - normal at 0.81. urinalysis normal but low specific gravity. ultrasound - two punctate echogenic foci within the left kidney. random microalbumin- normal. causes ?

Low urine specificity means your urine is diluted, i.e. your fluid intake is high. Two punctuate echogenic foci mean you have tiny stones in your left kidney. Your kidney function is normal by serum creatinine, BUN and cystatin-C. High fluid intake, as you have done, is the best way to prevent further stone development. You should see an expert in kidney stone for further care (tx and prevention).