title: Use of the triiodothyronine suppression test for diagnosis of hyperthyroidism in ill cats that have serum concentration of iodothyronines within normal range.
abstract: Administration of triiodothyronine (liothyronine, 15 micrograms, q 8 h, for 6 treatments) caused marked decrease in serum concentration of thyroxine (T4) and estimates of free T4 (fT4) concentration in clinically normal cats. A prospective clinical study was done to evaluate the use of this suppression test for diagnosis of hyperthyroidism in cats with clinical signs suggestive of the disease, but lacking high serum concentration of iodothyronines. Twenty-three cats were confirmed as hyperthyroid on the basis of histologic changes in the thyroid gland or clinical improvement in response to administration of methimazole. Mean +/- SD serum concentration of T4 (34.3 +/- 12.7 to 31.3 +/- 11.5 nmol/L) and estimate of fT4 concentration (26.6 +/- 6.4 to 25.6 +/- 6.9 pmol/L) did not change after administration of liothyronine to these cats. Twenty-three cats were classified as nonhyperthyroid by histologic confirmation of other disease, abnormal results of other diagnostic tests that strongly supported primary disease other than hyperthyroidism, or spontaneous remission of weight loss without treatment. Mean +/- SD serum concentration of T4 (27.9 +/- 10.3 to 11.7 +/- 6.4 nmol/L) and estimate of fT4 concentration (21.7 +/- 5.4 to 10.4 +/- 4.4 pmol/L) decreased significantly (P less than 0.001) in response to administration of liothyronine. Discriminant analysis was used to identify variables from iodothyronine assays (eg, absolute concentration of T4 or absolute estimate of fT4 concentration, or changes of T4 or fT4 concentration) that provided the best diagnostic sensitivity and specificity.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Animal Health Diagnostic Laboratory, College of Veterinary Medicine, Michigan State University, East Lansing 48824-1316.
authors.forename: K R
authors.initials: KR
authors.lastname: Refsal
authors.forename: R F
authors.initials: RF
authors.lastname: Nachreiner
authors.forename: B E
authors.initials: BE
authors.lastname: Stein
authors.forename: C E
authors.initials: CE
authors.lastname: Currigan
authors.forename: A N
authors.initials: AN
authors.lastname: Zendel
authors.forename: E L
authors.initials: EL
authors.lastname: Thacker
mesh_terms: D000818:Animals; D002371:Cat Diseases / Q000175:diagnosis*; D002415:Cats; D016002:Discriminant Analysis; D005069:Evaluation Studies as Topic; D005188:False Negative Reactions; D005189:False Positive Reactions; D005260:Female; D006980:Hyperthyroidism / Q000175:diagnosis / Q000662:veterinary*; D008297:Male; D011237:Predictive Value of Tests; D011446:Prospective Studies; D013970:Thyronines / Q000097:blood*; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
chemical_list: D013970:Thyronines; D014284:Triiodothyronine; D013974:Thyroxine