Evaluation of patients with possible thyroid disease can be done cost-effectively using a testing algorithm based on thyrotropin (TSH) levels initially, followed by additional testing as needed.
TSH
Additional Testing
Diagnosis
normal
none needed
euthyroid
decreased
free thyroxine increased
hyperthyroid
free thyroxine normal (triiodothyronine levels)
T3 thyrotoxicosis
free thyroxine decreased
non-thyroid illness or drugs
increased
free thyroxine increased
thyroid resistance or pituitary tumor
free thyroxine normal
subclinical hypothyroid
free thyroxine decreased
hypothyroid
TSH use in other conditions:
(1) can be used to monitor thyroid hormone replacement
(2) not recommended for following treatment of hyperthyroidism
Drugs Affecting TSH Levels
Decreased TSH
Increased TSH
bromocriptine
amiodarone
carbamazepine
clomiphene
corticosteroids
haloperidol
cyproheptadine
iodides
dopamine
lithium
heparin
methimazole
levodopa
metoclopramide
metergoline
morphine
phentolamine
oral radiographic dyes
somatostatin
phenothiazines
triiodothyroxine
propylthiouracil
Limitations to algorithm:
• Some patients with hypothalamic-pituitary disease may be hypothyroid and not be detected by the algorithm
• Some TSH-producing pituitary adenomas may be hyperthyroid yet have normal TSH value on immunoassay (functionally active TSH not detected by antibodies in immunoassays)
•Acute severe psychiatric illness may be associated with low TSH levels
• Recovery following radioiodine therapy
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