Directly, hypothyroidism causes an approximately 40% fall in GFR14 due to its regulation of the adrenergic and dopaminergic receptors on the renal tubular cells,15 which have an effect on the renin-angiotensin-aldosterone axis, renin release, and angiotensinase activity.7,16 The low GFR results in an increase in serum creatinine levels.4 Another study6 noted a fall in serum creatinine after thyroid hormone replacement along with an increase in GFR and estimated RPF. This evidence concerns the gene REN and hypothyroidism.