USMLE Forum Archives - USMLE Step 3 - TSH
TSH
meduploader - 06-29-09 15:30
TSH: The single best screening test for evaluating thyroid function is TSH. Low levels most commonly represent hyperthyroidism; high levels suggest hypothyroidism.
If there is 2° (pituitary) thyroid dysfunction, the TSH is unreliable, and FT4 is used instead.
If TSH is abnormal, the next step is to check a FT4.
If TSH is low and FT4 is normal, then check a total or free T3 (TT3 or FT3) to rule out “T3 thyrotoxicosis.” TT3 or FT3 is often low in euthyroid sick syndrome and amiodarone-induced hypothyroidism. It is not necessary to check TT3 or FT3 in the evaluation of routine hypothyroidism.
Preferred Screening test for suspected HYPO/HYPER Thyroidism
Preferred Follow-up test for patients receiving therapy for either hypo or hyperthyrodism or pts who had thyroid cancer therapy
If TSH High à possible Primary hypothyroidism or rarely, secondary hyperthyroidism
If TSH low à possible Primary hyperthyroidism or rarely, secondary hypothyroidism
If TSH low in pt on treatment for hypothyroidism à reduce dose of levothyroxine. ( usually in increments of 25mcg each time)
If TSH high in a pt on treatment for hypothyroidism à Increase dose of levothyroxine. ( usually in increments of 25mcg each time)
If TSH low in pt on treatment for hyperthyroidism à Increase dose of Propylthiouracil/ Methimazole ( or may indicate inadequate therapy)
If TSH high in a pt on treatment for hyperthyroidism à Reduce dose of Propylthiouracil/ Methimazole ( Indicates excess antithyroid therapy.
If Radioiodine therapy was chosen, then aim is to make the pt Hypothyroid in order to achieve good cure rates in Graves thyrotoxicosis à in that case, you need to start levothyroxine post radioiodine therapy or post surgically)
Obtain screening TSH in patients with conditions that may be explained by or aggravated by hyperthyroidism :
Unexplained weight loss
Anxiety or sleep disturbance
Tachycardia, including supraventricular tachycardia and new onset atrial fibrillation
Osteoporosis
Obtain screening TSH in patients with conditions that may be explained by or aggravated by hypothyroidism :
History of thyroid disease
Autoimmune disease (R/O co-existent hashimatos)
Unexplained depression
Cognitive dysfunction ( dementia, delirium)
Hypercholesterolemia
Unexplained constipation
Screen in early pregnancy
If TSH low but Free T4 normal à get T3 level. If T3 high à T3 toxicosis. If T3 normal à subclinical Hyperthyroidism.
If TSH high but Free T4 normal à Sublinical Hypothyroidism ( Treat only if symptoms are present or TSH > 10mU/l , For TSH between 5 to 10 à consider Rx if TPO antibodies high/ pt has goiter or high serum LDL)
In cases of subclinical hypothyroidism, presence of anti-TPO antibodies predicts progression to overt Hypothyroidism ( Hashimatos)
meduploader - 06-29-09 15:30
TSH: The single best screening test for evaluating thyroid function is TSH. Low levels most commonly represent hyperthyroidism; high levels suggest hypothyroidism.
If there is 2° (pituitary) thyroid dysfunction, the TSH is unreliable, and FT4 is used instead.
If TSH is abnormal, the next step is to check a FT4.
If TSH is low and FT4 is normal, then check a total or free T3 (TT3 or FT3) to rule out “T3 thyrotoxicosis.” TT3 or FT3 is often low in euthyroid sick syndrome and amiodarone-induced hypothyroidism. It is not necessary to check TT3 or FT3 in the evaluation of routine hypothyroidism.
Preferred Screening test for suspected HYPO/HYPER Thyroidism
Preferred Follow-up test for patients receiving therapy for either hypo or hyperthyrodism or pts who had thyroid cancer therapy
If TSH High à possible Primary hypothyroidism or rarely, secondary hyperthyroidism
If TSH low à possible Primary hyperthyroidism or rarely, secondary hypothyroidism
If TSH low in pt on treatment for hypothyroidism à reduce dose of levothyroxine. ( usually in increments of 25mcg each time)
If TSH high in a pt on treatment for hypothyroidism à Increase dose of levothyroxine. ( usually in increments of 25mcg each time)
If TSH low in pt on treatment for hyperthyroidism à Increase dose of Propylthiouracil/ Methimazole ( or may indicate inadequate therapy)
If TSH high in a pt on treatment for hyperthyroidism à Reduce dose of Propylthiouracil/ Methimazole ( Indicates excess antithyroid therapy.
If Radioiodine therapy was chosen, then aim is to make the pt Hypothyroid in order to achieve good cure rates in Graves thyrotoxicosis à in that case, you need to start levothyroxine post radioiodine therapy or post surgically)
Obtain screening TSH in patients with conditions that may be explained by or aggravated by hyperthyroidism :
Unexplained weight loss
Anxiety or sleep disturbance
Tachycardia, including supraventricular tachycardia and new onset atrial fibrillation
Osteoporosis
Obtain screening TSH in patients with conditions that may be explained by or aggravated by hypothyroidism :
History of thyroid disease
Autoimmune disease (R/O co-existent hashimatos)
Unexplained depression
Cognitive dysfunction ( dementia, delirium)
Hypercholesterolemia
Unexplained constipation
Screen in early pregnancy
If TSH low but Free T4 normal à get T3 level. If T3 high à T3 toxicosis. If T3 normal à subclinical Hyperthyroidism.
If TSH high but Free T4 normal à Sublinical Hypothyroidism ( Treat only if symptoms are present or TSH > 10mU/l , For TSH between 5 to 10 à consider Rx if TPO antibodies high/ pt has goiter or high serum LDL)
In cases of subclinical hypothyroidism, presence of anti-TPO antibodies predicts progression to overt Hypothyroidism ( Hashimatos)
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Re: TSH mtniharika - 09-11-09 15:10 TSH levels are tested in the blood of patients suspected of suffering from excess (hyperthyroidism), or deficiency (hypothyroidism) of thyroid hormone. Generally, a standard reference range for TSH for adults is between 0.4 and 5.0 µIU/mL (equivalent to mIU/L), but values vary slightly among labs. The therapeutic target range TSH level for patients on treatment ranges between 0.3 to 3.0 mIU/L.[4] The interpretation depends also on what the blood levels of thyroid hormones (T3 and T4) are.
TSH levels for children normally start out much higher.
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