Egfr is 57... normal bun and creatinine. frequent urination and thirst. could it be diabetes insipidus? my urine is always clear. sg is 1.005

Workup plan: I'd ignore the estimated gfr; it is subscientific especially if BUN and creatinine are within normal limits. Trusting the urinalysis and urinary sediment are okay. Your next step will be a test to see if you can concentrate your urine; your physician will supervise. If you can't, you'll be given ADH (vasopressin) to see if that fixes things; this distinguishes pituitary from renal diabetes insipidus.