Association of iatrogenic hypothyroidism with azotemia and reduced survival time in cats treated for hyperthyroidism

J Vet Intern Med. 2010 Sep-Oct;24(5):1086-92. doi: 10.1111/j.1939-1676.2010.0566.x. Epub 2010 Jul 28.


Background: Iatrogenic hypothyroidism can occur after treatment of hyperthyroidism, and is correlated with a reduced glomerular filtration rate in humans and dogs.

Hypothesis: Cats with iatrogenic hypothyroidism after treatment for hyperthyroidism will have a greater incidence of azotemia than euthyroid cats.

Animals: Eighty client owned cats with hyperthyroidism.

Methods: Two retrospective studies. (1) Longitudinal study of 12 hyperthyroid cats treated with radioiodine (documented as euthyroid after treatment), to assess changes in plasma thyroid stimulating hormone (TSH) concentration over a 6-month follow-up period, (2) Cross-sectional study of 75 hyperthyroid cats (documented as euthyroid) 6 months after commencement of treatment for hyperthyroidism to identify the relationship between thyroid status and the development of azotemia. Kaplan-Meier survival analysis was performed to identify relationships between thyroid and renal status and survival.

Results: Plasma TSH concentrations were not suppressed in 7 of 8 cats with hypothyroidism 3 months after radioiodine treatment. The proportion of cats with azotemia was significantly (P= .028) greater in the hypothyroid (16 of 28) than the euthyroid group (14 of 47). Twenty-eight of 41 cats (68%) with plasma TT4 concentration below the laboratory reference range had an increased plasma TSH concentration. Hypothyroid cats that developed azotemia within the follow-up period had significantly (P= .018) shorter survival times (median survival time 456 days, range 231-1589 days) than those that remained nonazotemic (median survival time 905 days, range 316-1869 days).

Conclusions and clinical importance: Iatrogenic hypothyroidism appears to contribute to the development of azotemia after treatment of hyperthyroidism, and reduced survival time in azotemic cats.

MeSH terms

  • Animals
  • Azotemia / etiology
  • Azotemia / veterinary*
  • Cat Diseases / etiology*
  • Cat Diseases / pathology
  • Cats
  • Hyperthyroidism / complications
  • Hyperthyroidism / veterinary*
  • Hypothyroidism / complications
  • Hypothyroidism / veterinary*
  • Iatrogenic Disease / veterinary*
  • Iodine / adverse effects*
  • Iodine Radioisotopes / adverse effects
  • Longevity
  • Risk Factors


  • Iodine Radioisotopes
  • Iodine