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TSH (Thyroid Stimulating Hormone), with reflex
MessagePerforming Lab: Central Lab, Hudson, Lakeview, Regions, Sartell, Westfields
Test Code
0191
Alias/See Also
Sunquest: TSHSR; TSH, 3rd Generation with reflex, Thyroid Cascade
CPT Codes
84443
Includes
If TSH is <0.30 or >4.50, T4FRE will automatically be orderded.
Preferred Specimen
0.3 mL Lithium Heparin Plasma (light green-top) tube
Minimum Volume
0.2 mL
Other Acceptable Specimens
Serum (gold-top) tube
Transport Temperature
Refrigerated
Specimen Stability
Room temperature (24 hours), Refrigerated (7 days), Frozen (6 months)
Methodology
Chemiluminescent microparticle immunoassay (CMIA)
Setup Schedule
Hospital: Daily
Clinics: Monday - Friday
Clinics: Monday - Friday
Report Available
Same Day
Reference Range
| 0.30-4.50 uIU/mL | |
Clinical Significance
TSH secretion by the anterior pituitary is controlled by thyrotropin releasing hormone, a tripeptide produced by the hypothalamus. TSH stimulates the production of thyroxine (T4) and triiodothyronine (T3) by the thyroid gland. The circulating free fractions of T4 and T3 in turn regulate the secretion of TSH by a negative feedback mechanism at the pituitary and possibly the hypothalamus. In the presence of normal pituitary function, TSH is the preferred initial test in the evaluation of thyroid function.
Patients with normal TSH are considered euthyroid and no additional testing is indicated.
Patients with an elevated TSH level may have primary hypothyroidism and should be evaluated with a Free T4. Free T4 helps distinguish clinical from subclinical disease. A low Free T4 in this setting is consistent with primary hypothyroidism whereas a normal Free T4 indicates subclinical primary hypothyroidism.
Patients with a low TSH may have primary hyperthyroidism. Further evaluation with a Free T4 will help distinguish clinical from subclinical disease. In the setting of a low TSH, an elevated Free T4 is consistent with primary Hyperthyroidism. A low TSH and normal Free T4 can occur with T3 thyrotoxicosis or with primary subclinical Hyperthyroidism. The addition of Free T3 measurement helps to distinguish between these two entities.
TSH levels can also be utilized in the monitoring of thyroid hormone replacement therapy with the goal of therapy to return TSH levels to within the normal reference range.
Patients with normal TSH are considered euthyroid and no additional testing is indicated.
Patients with an elevated TSH level may have primary hypothyroidism and should be evaluated with a Free T4. Free T4 helps distinguish clinical from subclinical disease. A low Free T4 in this setting is consistent with primary hypothyroidism whereas a normal Free T4 indicates subclinical primary hypothyroidism.
Patients with a low TSH may have primary hyperthyroidism. Further evaluation with a Free T4 will help distinguish clinical from subclinical disease. In the setting of a low TSH, an elevated Free T4 is consistent with primary Hyperthyroidism. A low TSH and normal Free T4 can occur with T3 thyrotoxicosis or with primary subclinical Hyperthyroidism. The addition of Free T3 measurement helps to distinguish between these two entities.
TSH levels can also be utilized in the monitoring of thyroid hormone replacement therapy with the goal of therapy to return TSH levels to within the normal reference range.
