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Am Fam Physician. 1999;59(9):2588

The decreases in renal plasma flow and glomerular filtration rate (GFR) that accompany hypothyroidism are believed to be related to the generalized hypodynamic state of the circulatory system in hypothroidism. Elevation of serum creatinine levels is not generally mentioned as an abnormality that occurs in association with hypothyroidism, although reports of such an association exist. Kreisman and Hennessey evaluated serum creatinine levels in 24 consecutive patients with iatrogenically induced hypothyroidism in conjunction with treatment of thyroid carcinoma.

Serum creatinine concentrations and thyroid function tests were determined before, during and after the brief period of severe hypothyroidism, when no thyroid hormone was administered for the two weeks before administration of radioiodine. Severe acute hypothyroidism was defined as a thyroid-stimulating hormone value greater than 40 μU per mL (40 mIU per L); normal range: 0.3 to 5.0 μU per mL (0.3 to 5.0 mIU per L).

The creatinine level was increased in 26 of 29 episodes (90 percent) of hypothyroidism in a subgroup of 15 patients in whom creatinine values were obtained during the euthyroid state before induction of hypothyroidism. The mean hypothyroid creatinine values were significantly greater during hypothyroidism than during the euthyroid state. Creatinine values increased by 34.4 percent after induction of hypothyroidism.

Similarly, serum creatinine levels were significantly higher during hypothyroidism in a subgroup in which creatinine levels were determined both during hypothyroidism and after the return to euthyroidism. The mean hypothyroid creatinine value was significantly greater in 33 of the 36 episodes (92 percent). The mean hypothyroid value was 1.15 mg per dL (102 μmol per L), compared with 0.85 mg per dL (75 μmol per L) during the euthyroid state following the period of hypothyroidism. Serum creatinine values above the normal range occurred in six of the 36 hypothyroid episodes.

The rise in creatinine levels during hypothyroidism was not associated with abnormal creatine kinase levels or other evidence of hypothyroid myopathy or intrinsic renal disease. The findings demonstrated that very little time is required for the development of elevated serum creatinine levels during the hypothyroid state. The results argue against the previously held notion of a net unchanged creatinine value because of a balance between the decrease in renal clearance and a decrease in creatinine generation.

The authors conclude that the hypothyroid state is associated with a consistent elevation in the serum creatinine level, presumably related to a decrease in the GFR. The changes in serum creatinine levels develop rapidly and appear to be reversible. It may be clinically relevant to know of this association in that it could account for creatinine elevation in a patient with hypothyroidism. It should also alert the clinician to consider evaluation of thyroid function in a patient who has a modest serum creatinine elevation but whose thyroid status is unknown.

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