['< sod > the bun : cr in postrenal azotemia is initially > 0 15. over time the bun : cr will decrease due to tubule specific epithelial damage. < ref > { { cite web | url = http : / / www. consultation. ayurvediccure. com / types - of - azotemia / | title = types of azotemia | [UNK] website = ayurvediccure. com } } < / ref > the increased [ [ [UNK] nephron ] ] tubular pressure causes increased reabsorption of urea, elevating it abnormally relative to creatinine. < ref name = from goljanpath / > < http eod > < sod > the bun : cr in postrenal azotemia is initially > 15. the increased [ [ nephron ] ] tubular pressure ( due to fluid back - up ) causes increased reabsorption of urea, elevating it abnormally relative to creatinine. < ref family name = " goljanpath " / > persistent obstruction damages toward the tubular epithelium over time, and renal functional azotemia normally will result with a decreased bun : cr ratio. < ref > { { cite web | url = http : / / www. consultation. ayurvediccure. com / types - of - azotemia / | title = types of azotemia | website = ayurvediccure. com } } < / ref > < eod >']